First steps towards character LCD

1 files changed, 2029 insertions, 0 deletions

diff --git a/3rd-party/bcm2835.c b/3rd-party/bcm2835.c
new file mode 100644
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+/* bcm2835.c
+// C and C++ support for Broadcom BCM 2835 as used in Raspberry Pi
+// http://elinux.org/RPi_Low-level_peripherals
+// http://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
+//
+// Author: Mike McCauley
+// Copyright (C) 2011-2013 Mike McCauley
+// $Id: bcm2835.c,v 1.28 2020/01/11 05:07:13 mikem Exp mikem $
+*/
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#include <sys/types.h>
+
+#define BCK2835_LIBRARY_BUILD
+#include "bcm2835.h"
+
+/* This define enables a little test program (by default a blinking output on pin RPI_GPIO_PIN_11)
+// You can do some safe, non-destructive testing on any platform with:
+// gcc bcm2835.c -D BCM2835_TEST
+// ./a.out
+*/
+/*#define BCM2835_TEST*/
+
+/* Uncommenting this define compiles alternative I2C code for the version 1 RPi
+// The P1 header I2C pins are connected to SDA0 and SCL0 on V1.
+// By default I2C code is generated for the V2 RPi which has SDA1 and SCL1 connected.
+*/
+/* #define I2C_V1*/
+
+/* Physical address and size of the peripherals block
+// May be overridden on RPi2
+*/
+off_t bcm2835_peripherals_base = BCM2835_PERI_BASE;
+size_t bcm2835_peripherals_size = BCM2835_PERI_SIZE;
+
+/* Virtual memory address of the mapped peripherals block 
+ */
+uint32_t *bcm2835_peripherals = (uint32_t *)MAP_FAILED;
+
+/* And the register bases within the peripherals block
+ */
+volatile uint32_t *bcm2835_gpio        = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_pwm         = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_clk         = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_pads        = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_spi0        = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_bsc0        = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_bsc1        = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_st	       = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_aux	       = (uint32_t *)MAP_FAILED;
+volatile uint32_t *bcm2835_spi1        = (uint32_t *)MAP_FAILED;
+
+
+
+/* This variable allows us to test on hardware other than RPi.
+// It prevents access to the kernel memory, and does not do any peripheral access
+// Instead it prints out what it _would_ do if debug were 0
+ */
+static uint8_t debug = 0;
+
+/* RPI 4 has different pullup registers - we need to know if we have that type */
+
+static uint8_t pud_type_rpi4 = 0;
+
+/* RPI 4 has different pullup operation - make backwards compat */
+
+static uint8_t pud_compat_setting = BCM2835_GPIO_PUD_OFF;
+
+/* I2C The time needed to transmit one byte. In microseconds.
+ */
+static int i2c_byte_wait_us = 0;
+
+/* SPI bit order. BCM2835 SPI0 only supports MSBFIRST, so we instead 
+ * have a software based bit reversal, based on a contribution by Damiano Benedetti
+ */
+static uint8_t bcm2835_spi_bit_order = BCM2835_SPI_BIT_ORDER_MSBFIRST;
+static uint8_t bcm2835_byte_reverse_table[] = 
+{
+    0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
+    0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
+    0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
+    0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
+    0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
+    0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
+    0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
+    0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
+    0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
+    0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
+    0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
+    0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
+    0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
+    0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
+    0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
+    0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
+    0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
+    0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
+    0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
+    0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
+    0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
+    0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
+    0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
+    0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
+    0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
+    0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
+    0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
+    0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
+    0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
+    0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
+    0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
+    0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
+};
+
+static uint8_t bcm2835_correct_order(uint8_t b)
+{
+    if (bcm2835_spi_bit_order == BCM2835_SPI_BIT_ORDER_LSBFIRST)
+	return bcm2835_byte_reverse_table[b];
+    else
+	return b;
+}
+
+#ifdef BCM2835_HAVE_LIBCAP
+#include <sys/capability.h>
+static int bcm2835_has_capability(cap_value_t capability)
+{
+    int ok = 0;
+    cap_t cap = cap_get_proc();
+    if (cap)
+    {
+        cap_flag_value_t value;
+        if (cap_get_flag(cap,capability,CAP_EFFECTIVE,&value) == 0 && value == CAP_SET)
+            ok = 1;
+       cap_free(cap);
+    }
+    return ok;
+}
+#endif
+
+/*
+// Low level register access functions
+*/
+
+/* Function to return the pointers to the hardware register bases */
+uint32_t* bcm2835_regbase(uint8_t regbase)
+{
+    switch (regbase)
+    {
+	case BCM2835_REGBASE_ST:
+	    return (uint32_t *)bcm2835_st;
+	case BCM2835_REGBASE_GPIO:
+	    return (uint32_t *)bcm2835_gpio;
+	case BCM2835_REGBASE_PWM:
+	    return (uint32_t *)bcm2835_pwm;
+	case BCM2835_REGBASE_CLK:
+	    return (uint32_t *)bcm2835_clk;
+	case BCM2835_REGBASE_PADS:
+	    return (uint32_t *)bcm2835_pads;
+	case BCM2835_REGBASE_SPI0:
+	    return (uint32_t *)bcm2835_spi0;
+	case BCM2835_REGBASE_BSC0:
+	    return (uint32_t *)bcm2835_bsc0;
+	case BCM2835_REGBASE_BSC1:
+	    return (uint32_t *)bcm2835_st;
+	case BCM2835_REGBASE_AUX:
+	    return (uint32_t *)bcm2835_aux;
+	case BCM2835_REGBASE_SPI1:
+	    return (uint32_t *)bcm2835_spi1;
+
+    }
+    return (uint32_t *)MAP_FAILED;
+}
+
+void  bcm2835_set_debug(uint8_t d)
+{
+    debug = d;
+}
+
+unsigned int bcm2835_version(void) 
+{
+    return BCM2835_VERSION;
+}
+
+/* Read with memory barriers from peripheral
+ *
+ */
+uint32_t bcm2835_peri_read(volatile uint32_t* paddr)
+{
+    uint32_t ret;
+    if (debug)
+    {
+		printf("bcm2835_peri_read  paddr %p\n", (void *) paddr);
+		return 0;
+    }
+    else
+    {
+       __sync_synchronize();
+       ret = *paddr;
+       __sync_synchronize();
+       return ret;
+    }
+}
+
+/* read from peripheral without the read barrier
+ * This can only be used if more reads to THE SAME peripheral
+ * will follow.  The sequence must terminate with memory barrier
+ * before any read or write to another peripheral can occur.
+ * The MB can be explicit, or one of the barrier read/write calls.
+ */
+uint32_t bcm2835_peri_read_nb(volatile uint32_t* paddr)
+{
+    if (debug)
+    {
+	printf("bcm2835_peri_read_nb  paddr %p\n", paddr);
+	return 0;
+    }
+    else
+    {
+	return *paddr;
+    }
+}
+
+/* Write with memory barriers to peripheral
+ */
+
+void bcm2835_peri_write(volatile uint32_t* paddr, uint32_t value)
+{
+    if (debug)
+    {
+	printf("bcm2835_peri_write paddr %p, value %08X\n", paddr, value);
+    }
+    else
+    {
+        __sync_synchronize();
+        *paddr = value;
+        __sync_synchronize();
+    }
+}
+
+/* write to peripheral without the write barrier */
+void bcm2835_peri_write_nb(volatile uint32_t* paddr, uint32_t value)
+{
+    if (debug)
+    {
+	printf("bcm2835_peri_write_nb paddr %p, value %08X\n",
+                paddr, value);
+    }
+    else
+    {
+	*paddr = value;
+    }
+}
+
+/* Set/clear only the bits in value covered by the mask
+ * This is not atomic - can be interrupted.
+ */
+void bcm2835_peri_set_bits(volatile uint32_t* paddr, uint32_t value, uint32_t mask)
+{
+    uint32_t v = bcm2835_peri_read(paddr);
+    v = (v & ~mask) | (value & mask);
+    bcm2835_peri_write(paddr, v);
+}
+
+/*
+// Low level convenience functions
+*/
+
+/* Function select
+// pin is a BCM2835 GPIO pin number NOT RPi pin number
+//      There are 6 control registers, each control the functions of a block
+//      of 10 pins.
+//      Each control register has 10 sets of 3 bits per GPIO pin:
+//
+//      000 = GPIO Pin X is an input
+//      001 = GPIO Pin X is an output
+//      100 = GPIO Pin X takes alternate function 0
+//      101 = GPIO Pin X takes alternate function 1
+//      110 = GPIO Pin X takes alternate function 2
+//      111 = GPIO Pin X takes alternate function 3
+//      011 = GPIO Pin X takes alternate function 4
+//      010 = GPIO Pin X takes alternate function 5
+//
+// So the 3 bits for port X are:
+//      X / 10 + ((X % 10) * 3)
+*/
+void bcm2835_gpio_fsel(uint8_t pin, uint8_t mode)
+{
+    /* Function selects are 10 pins per 32 bit word, 3 bits per pin */
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPFSEL0/4 + (pin/10);
+    uint8_t   shift = (pin % 10) * 3;
+    uint32_t  mask = BCM2835_GPIO_FSEL_MASK << shift;
+    uint32_t  value = mode << shift;
+    bcm2835_peri_set_bits(paddr, value, mask);
+}
+
+/* Set output pin */
+void bcm2835_gpio_set(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPSET0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    bcm2835_peri_write(paddr, 1 << shift);
+}
+
+/* Clear output pin */
+void bcm2835_gpio_clr(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPCLR0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    bcm2835_peri_write(paddr, 1 << shift);
+}
+
+/* Set all output pins in the mask */
+void bcm2835_gpio_set_multi(uint32_t mask)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPSET0/4;
+    bcm2835_peri_write(paddr, mask);
+}
+
+/* Clear all output pins in the mask */
+void bcm2835_gpio_clr_multi(uint32_t mask)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPCLR0/4;
+    bcm2835_peri_write(paddr, mask);
+}
+
+/* Read input pin */
+uint8_t bcm2835_gpio_lev(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPLEV0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = bcm2835_peri_read(paddr);
+    return (value & (1 << shift)) ? HIGH : LOW;
+}
+
+/* See if an event detection bit is set
+// Sigh cant support interrupts yet
+*/
+uint8_t bcm2835_gpio_eds(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPEDS0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = bcm2835_peri_read(paddr);
+    return (value & (1 << shift)) ? HIGH : LOW;
+}
+
+uint32_t bcm2835_gpio_eds_multi(uint32_t mask)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPEDS0/4;
+    uint32_t value = bcm2835_peri_read(paddr);
+    return (value & mask);
+}
+
+/* Write a 1 to clear the bit in EDS */
+void bcm2835_gpio_set_eds(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPEDS0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_write(paddr, value);
+}
+
+void bcm2835_gpio_set_eds_multi(uint32_t mask)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPEDS0/4;
+    bcm2835_peri_write(paddr, mask);
+}
+
+/* Rising edge detect enable */
+void bcm2835_gpio_ren(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPREN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, value, value);
+}
+void bcm2835_gpio_clr_ren(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPREN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, 0, value);
+}
+
+/* Falling edge detect enable */
+void bcm2835_gpio_fen(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPFEN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, value, value);
+}
+void bcm2835_gpio_clr_fen(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPFEN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, 0, value);
+}
+
+/* High detect enable */
+void bcm2835_gpio_hen(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPHEN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, value, value);
+}
+void bcm2835_gpio_clr_hen(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPHEN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, 0, value);
+}
+
+/* Low detect enable */
+void bcm2835_gpio_len(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPLEN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, value, value);
+}
+void bcm2835_gpio_clr_len(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPLEN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, 0, value);
+}
+
+/* Async rising edge detect enable */
+void bcm2835_gpio_aren(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPAREN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, value, value);
+}
+void bcm2835_gpio_clr_aren(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPAREN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, 0, value);
+}
+
+/* Async falling edge detect enable */
+void bcm2835_gpio_afen(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPAFEN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, value, value);
+}
+void bcm2835_gpio_clr_afen(uint8_t pin)
+{
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPAFEN0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    uint32_t value = 1 << shift;
+    bcm2835_peri_set_bits(paddr, 0, value);
+}
+
+/* Set pullup/down */
+void bcm2835_gpio_pud(uint8_t pud)
+{
+    if( pud_type_rpi4 )
+    {
+        pud_compat_setting = pud;
+    }
+    else {
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPPUD/4;
+    bcm2835_peri_write(paddr, pud);
+}
+}
+
+/* Pullup/down clock
+// Clocks the value of pud into the GPIO pin
+*/
+void bcm2835_gpio_pudclk(uint8_t pin, uint8_t on)
+{
+    if( pud_type_rpi4 )
+    {
+        if( on )
+            bcm2835_gpio_set_pud( pin, pud_compat_setting);
+    }
+    else
+    {
+    volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPPUDCLK0/4 + pin/32;
+    uint8_t shift = pin % 32;
+    bcm2835_peri_write(paddr, (on ? 1 : 0) << shift);
+}
+}
+
+/* Read GPIO pad behaviour for groups of GPIOs */
+uint32_t bcm2835_gpio_pad(uint8_t group)
+{
+  if (bcm2835_pads == MAP_FAILED)
+    return 0;
+  
+    volatile uint32_t* paddr = bcm2835_pads + BCM2835_PADS_GPIO_0_27/4 + group;
+    return bcm2835_peri_read(paddr);
+}
+
+/* Set GPIO pad behaviour for groups of GPIOs
+// powerup value for all pads is
+// BCM2835_PAD_SLEW_RATE_UNLIMITED | BCM2835_PAD_HYSTERESIS_ENABLED | BCM2835_PAD_DRIVE_8mA
+*/
+void bcm2835_gpio_set_pad(uint8_t group, uint32_t control)
+{
+  if (bcm2835_pads == MAP_FAILED)
+    return;
+  
+    volatile uint32_t* paddr = bcm2835_pads + BCM2835_PADS_GPIO_0_27/4 + group;
+    bcm2835_peri_write(paddr, control | BCM2835_PAD_PASSWRD);
+}
+
+/* Some convenient arduino-like functions
+// milliseconds
+*/
+void bcm2835_delay(unsigned int millis)
+{
+    struct timespec sleeper;
+    
+    sleeper.tv_sec  = (time_t)(millis / 1000);
+    sleeper.tv_nsec = (long)(millis % 1000) * 1000000;
+    nanosleep(&sleeper, NULL);
+}
+
+/* microseconds */
+void bcm2835_delayMicroseconds(uint64_t micros)
+{
+    struct timespec t1;
+    uint64_t        start;
+	
+    if (debug)
+    {
+	/* Cant access sytem timers in debug mode */
+	printf("bcm2835_delayMicroseconds %lld\n", (long long int) micros);
+	return;
+    }
+
+    /* Calling nanosleep() takes at least 100-200 us, so use it for
+    // long waits and use a busy wait on the System Timer for the rest.
+    */
+    start =  bcm2835_st_read();
+   
+    /* Not allowed to access timer registers (result is not as precise)*/
+    if (start==0)
+    {
+	t1.tv_sec = 0;
+	t1.tv_nsec = 1000 * (long)(micros);
+	nanosleep(&t1, NULL);
+	return;
+    }
+
+    if (micros > 450)
+    {
+	t1.tv_sec = 0;
+	t1.tv_nsec = 1000 * (long)(micros - 200);
+	nanosleep(&t1, NULL);
+    }    
+  
+    bcm2835_st_delay(start, micros);
+}
+
+/*
+// Higher level convenience functions
+*/
+
+/* Set the state of an output */
+void bcm2835_gpio_write(uint8_t pin, uint8_t on)
+{
+    if (on)
+	bcm2835_gpio_set(pin);
+    else
+	bcm2835_gpio_clr(pin);
+}
+
+/* Set the state of a all 32 outputs in the mask to on or off */
+void bcm2835_gpio_write_multi(uint32_t mask, uint8_t on)
+{
+    if (on)
+	bcm2835_gpio_set_multi(mask);
+    else
+	bcm2835_gpio_clr_multi(mask);
+}
+
+/* Set the state of a all 32 outputs in the mask to the values in value */
+void bcm2835_gpio_write_mask(uint32_t value, uint32_t mask)
+{
+    bcm2835_gpio_set_multi(value & mask);
+    bcm2835_gpio_clr_multi((~value) & mask);
+}
+
+/* Set the pullup/down resistor for a pin
+//
+// The GPIO Pull-up/down Clock Registers control the actuation of internal pull-downs on
+// the respective GPIO pins. These registers must be used in conjunction with the GPPUD
+// register to effect GPIO Pull-up/down changes. The following sequence of events is
+// required:
+// 1. Write to GPPUD to set the required control signal (i.e. Pull-up or Pull-Down or neither
+// to remove the current Pull-up/down)
+// 2. Wait 150 cycles ? this provides the required set-up time for the control signal
+// 3. Write to GPPUDCLK0/1 to clock the control signal into the GPIO pads you wish to
+// modify ? NOTE only the pads which receive a clock will be modified, all others will
+// retain their previous state.
+// 4. Wait 150 cycles ? this provides the required hold time for the control signal
+// 5. Write to GPPUD to remove the control signal
+// 6. Write to GPPUDCLK0/1 to remove the clock
+//
+// RPi has P1-03 and P1-05 with 1k8 pullup resistor
+//
+// RPI 4 uses a different PUD method - no clock
+
+*/
+void bcm2835_gpio_set_pud(uint8_t pin, uint8_t pud)
+{
+    if( pud_type_rpi4 )
+    {
+        int shiftbits = (pin & 0xf) << 1;
+        uint32_t bits;
+        uint32_t pull;
+        
+        switch (pud)
+        {
+           case BCM2835_GPIO_PUD_OFF:  pull = 0; break;
+           case BCM2835_GPIO_PUD_UP:   pull = 1; break;
+           case BCM2835_GPIO_PUD_DOWN: pull = 2; break;
+           default: return;
+        }
+                
+        volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPPUPPDN0/4 + (pin >> 4);
+        
+        bits = bcm2835_peri_read_nb( paddr );
+        bits &= ~(3 << shiftbits);
+        bits |= (pull << shiftbits);
+        
+        bcm2835_peri_write_nb( paddr, bits );
+        
+    } else
+    {
+    bcm2835_gpio_pud(pud);
+    delayMicroseconds(10);
+    bcm2835_gpio_pudclk(pin, 1);
+    delayMicroseconds(10);
+    bcm2835_gpio_pud(BCM2835_GPIO_PUD_OFF);
+    bcm2835_gpio_pudclk(pin, 0);
+}
+
+}
+
+
+uint8_t bcm2835_gpio_get_pud(uint8_t pin)
+{
+    uint8_t ret = BCM2835_GPIO_PUD_ERROR;
+    
+    if( pud_type_rpi4 )
+    {
+        uint32_t bits;
+        volatile uint32_t* paddr = bcm2835_gpio + BCM2835_GPPUPPDN0/4 + (pin >> 4);
+        bits = (bcm2835_peri_read_nb( paddr ) >> ((pin & 0xf)<<1)) & 0x3;
+        
+        switch (bits)
+        {
+            case 0: ret = BCM2835_GPIO_PUD_OFF; break;
+            case 1: ret = BCM2835_GPIO_PUD_UP; break;
+            case 2: ret = BCM2835_GPIO_PUD_DOWN; break;
+            default: ret = BCM2835_GPIO_PUD_ERROR;
+        }   
+    }
+    
+    return ret;
+}
+
+static void bcm2835_aux_spi_reset(void)
+ {
+     volatile uint32_t* cntl0 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL0/4;
+     volatile uint32_t* cntl1 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL1/4;
+ 
+     bcm2835_peri_write(cntl1, 0);
+     bcm2835_peri_write(cntl0, BCM2835_AUX_SPI_CNTL0_CLEARFIFO);
+}
+
+int bcm2835_spi_begin(void)
+{
+    volatile uint32_t* paddr;
+
+    if (bcm2835_spi0 == MAP_FAILED)
+      return 0; /* bcm2835_init() failed, or not root */
+    
+    /* Set the SPI0 pins to the Alt 0 function to enable SPI0 access on them */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_26, BCM2835_GPIO_FSEL_ALT0); /* CE1 */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_24, BCM2835_GPIO_FSEL_ALT0); /* CE0 */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_21, BCM2835_GPIO_FSEL_ALT0); /* MISO */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_19, BCM2835_GPIO_FSEL_ALT0); /* MOSI */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_23, BCM2835_GPIO_FSEL_ALT0); /* CLK */
+    
+    /* Set the SPI CS register to the some sensible defaults */
+    paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
+    bcm2835_peri_write(paddr, 0); /* All 0s */
+    
+    /* Clear TX and RX fifos */
+    bcm2835_peri_write_nb(paddr, BCM2835_SPI0_CS_CLEAR);
+
+    return 1; // OK
+}
+
+void bcm2835_spi_end(void)
+{  
+    /* Set all the SPI0 pins back to input */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_26, BCM2835_GPIO_FSEL_INPT); /* CE1 */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_24, BCM2835_GPIO_FSEL_INPT); /* CE0 */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_21, BCM2835_GPIO_FSEL_INPT); /* MISO */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_19, BCM2835_GPIO_FSEL_INPT); /* MOSI */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_23, BCM2835_GPIO_FSEL_INPT); /* CLK */
+}
+
+void bcm2835_spi_setBitOrder(uint8_t order)
+{
+    bcm2835_spi_bit_order = order;
+}
+
+/* defaults to 0, which means a divider of 65536.
+// The divisor must be a power of 2. Odd numbers
+// rounded down. The maximum SPI clock rate is
+// of the APB clock
+*/
+void bcm2835_spi_setClockDivider(uint16_t divider)
+{
+    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CLK/4;
+    bcm2835_peri_write(paddr, divider);
+}
+
+void bcm2835_spi_set_speed_hz(uint32_t speed_hz)
+{
+	uint16_t divider = (uint16_t) ((uint32_t) BCM2835_CORE_CLK_HZ / speed_hz);
+	divider &= 0xFFFE;
+	bcm2835_spi_setClockDivider(divider);
+}
+
+void bcm2835_spi_setDataMode(uint8_t mode)
+{
+    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
+    /* Mask in the CPO and CPHA bits of CS */
+    bcm2835_peri_set_bits(paddr, mode << 2, BCM2835_SPI0_CS_CPOL | BCM2835_SPI0_CS_CPHA);
+}
+
+/* Writes (and reads) a single byte to SPI */
+uint8_t bcm2835_spi_transfer(uint8_t value)
+{
+    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
+    volatile uint32_t* fifo = bcm2835_spi0 + BCM2835_SPI0_FIFO/4;
+    uint32_t ret;
+
+    /* This is Polled transfer as per section 10.6.1
+    // BUG ALERT: what happens if we get interupted in this section, and someone else
+    // accesses a different peripheral? 
+    // Clear TX and RX fifos
+    */
+    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_CLEAR, BCM2835_SPI0_CS_CLEAR);
+
+    /* Set TA = 1 */
+    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_TA, BCM2835_SPI0_CS_TA);
+
+    /* Maybe wait for TXD */
+    while (!(bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_TXD))
+	;
+
+    /* Write to FIFO, no barrier */
+    bcm2835_peri_write_nb(fifo, bcm2835_correct_order(value));
+
+    /* Wait for DONE to be set */
+    while (!(bcm2835_peri_read_nb(paddr) & BCM2835_SPI0_CS_DONE))
+	;
+
+    /* Read any byte that was sent back by the slave while we sere sending to it */
+    ret = bcm2835_correct_order(bcm2835_peri_read_nb(fifo));
+
+    /* Set TA = 0, and also set the barrier */
+    bcm2835_peri_set_bits(paddr, 0, BCM2835_SPI0_CS_TA);
+
+    return ret;
+}
+
+/* Writes (and reads) an number of bytes to SPI */
+void bcm2835_spi_transfernb(char* tbuf, char* rbuf, uint32_t len)
+{
+    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
+    volatile uint32_t* fifo = bcm2835_spi0 + BCM2835_SPI0_FIFO/4;
+    uint32_t TXCnt=0;
+    uint32_t RXCnt=0;
+
+    /* This is Polled transfer as per section 10.6.1
+    // BUG ALERT: what happens if we get interupted in this section, and someone else
+    // accesses a different peripheral? 
+    */
+
+    /* Clear TX and RX fifos */
+    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_CLEAR, BCM2835_SPI0_CS_CLEAR);
+
+    /* Set TA = 1 */
+    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_TA, BCM2835_SPI0_CS_TA);
+
+    /* Use the FIFO's to reduce the interbyte times */
+    while((TXCnt < len)||(RXCnt < len))
+    {
+        /* TX fifo not full, so add some more bytes */
+        while(((bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_TXD))&&(TXCnt < len ))
+        {
+	    bcm2835_peri_write_nb(fifo, bcm2835_correct_order(tbuf[TXCnt]));
+	    TXCnt++;
+        }
+        /* Rx fifo not empty, so get the next received bytes */
+        while(((bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_RXD))&&( RXCnt < len ))
+        {
+	    rbuf[RXCnt] = bcm2835_correct_order(bcm2835_peri_read_nb(fifo));
+	    RXCnt++;
+        }
+    }
+    /* Wait for DONE to be set */
+    while (!(bcm2835_peri_read_nb(paddr) & BCM2835_SPI0_CS_DONE))
+	;
+
+    /* Set TA = 0, and also set the barrier */
+    bcm2835_peri_set_bits(paddr, 0, BCM2835_SPI0_CS_TA);
+}
+
+/* Writes an number of bytes to SPI */
+void bcm2835_spi_writenb(const char* tbuf, uint32_t len)
+{
+    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
+    volatile uint32_t* fifo = bcm2835_spi0 + BCM2835_SPI0_FIFO/4;
+    uint32_t i;
+
+    /* This is Polled transfer as per section 10.6.1
+    // BUG ALERT: what happens if we get interupted in this section, and someone else
+    // accesses a different peripheral?
+    // Answer: an ISR is required to issue the required memory barriers.
+    */
+
+    /* Clear TX and RX fifos */
+    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_CLEAR, BCM2835_SPI0_CS_CLEAR);
+
+    /* Set TA = 1 */
+    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_TA, BCM2835_SPI0_CS_TA);
+
+    for (i = 0; i < len; i++)
+    {
+	/* Maybe wait for TXD */
+	while (!(bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_TXD))
+	    ;
+	
+	/* Write to FIFO, no barrier */
+	bcm2835_peri_write_nb(fifo, bcm2835_correct_order(tbuf[i]));
+	
+	/* Read from FIFO to prevent stalling */
+	while (bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_RXD)
+	    (void) bcm2835_peri_read_nb(fifo);
+    }
+    
+    /* Wait for DONE to be set */
+    while (!(bcm2835_peri_read_nb(paddr) & BCM2835_SPI0_CS_DONE)) {
+	while (bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_RXD)
+		(void) bcm2835_peri_read_nb(fifo);
+    };
+
+    /* Set TA = 0, and also set the barrier */
+    bcm2835_peri_set_bits(paddr, 0, BCM2835_SPI0_CS_TA);
+}
+
+/* Writes (and reads) an number of bytes to SPI
+// Read bytes are copied over onto the transmit buffer
+*/
+void bcm2835_spi_transfern(char* buf, uint32_t len)
+{
+    bcm2835_spi_transfernb(buf, buf, len);
+}
+
+void bcm2835_spi_chipSelect(uint8_t cs)
+{
+    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
+    /* Mask in the CS bits of CS */
+    bcm2835_peri_set_bits(paddr, cs, BCM2835_SPI0_CS_CS);
+}
+
+void bcm2835_spi_setChipSelectPolarity(uint8_t cs, uint8_t active)
+{
+    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
+    uint8_t shift = 21 + cs;
+    /* Mask in the appropriate CSPOLn bit */
+    bcm2835_peri_set_bits(paddr, active << shift, 1 << shift);
+}
+
+void bcm2835_spi_write(uint16_t data)
+{
+#if 0
+	char buf[2];
+
+	buf[0] = data >> 8;
+	buf[1] = data & 0xFF;
+
+	bcm2835_spi_transfern(buf, 2);
+#else
+    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
+    volatile uint32_t* fifo = bcm2835_spi0 + BCM2835_SPI0_FIFO/4;
+
+    /* Clear TX and RX fifos */
+    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_CLEAR, BCM2835_SPI0_CS_CLEAR);
+
+    /* Set TA = 1 */
+    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_TA, BCM2835_SPI0_CS_TA);
+
+	/* Maybe wait for TXD */
+	while (!(bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_TXD))
+	    ;
+
+	/* Write to FIFO */
+	bcm2835_peri_write_nb(fifo,  (uint32_t) data >> 8);
+	bcm2835_peri_write_nb(fifo,  data & 0xFF);
+
+
+    /* Wait for DONE to be set */
+    while (!(bcm2835_peri_read_nb(paddr) & BCM2835_SPI0_CS_DONE))
+	;
+
+    /* Set TA = 0, and also set the barrier */
+    bcm2835_peri_set_bits(paddr, 0, BCM2835_SPI0_CS_TA);
+#endif
+}
+
+int bcm2835_aux_spi_begin(void)
+{
+    volatile uint32_t* enable = bcm2835_aux + BCM2835_AUX_ENABLE/4;
+    volatile uint32_t* cntl0 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL0/4;
+    volatile uint32_t* cntl1 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL1/4;
+
+    if (bcm2835_spi1 == MAP_FAILED)
+	return 0; /* bcm2835_init() failed, or not root */
+
+    /* Set the SPI pins to the Alt 4 function to enable SPI1 access on them */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_36, BCM2835_GPIO_FSEL_ALT4);	/* SPI1_CE2_N */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_35, BCM2835_GPIO_FSEL_ALT4);	/* SPI1_MISO */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_38, BCM2835_GPIO_FSEL_ALT4);	/* SPI1_MOSI */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_40, BCM2835_GPIO_FSEL_ALT4);	/* SPI1_SCLK */
+
+    bcm2835_aux_spi_setClockDivider(bcm2835_aux_spi_CalcClockDivider(1000000));	// Default 1MHz SPI
+
+    bcm2835_peri_write(enable, BCM2835_AUX_ENABLE_SPI0);
+    bcm2835_peri_write(cntl1, 0);
+    bcm2835_peri_write(cntl0, BCM2835_AUX_SPI_CNTL0_CLEARFIFO);
+
+    return 1; /* OK */
+}
+
+void bcm2835_aux_spi_end(void)
+{
+    /* Set all the SPI1 pins back to input */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_36, BCM2835_GPIO_FSEL_INPT);	/* SPI1_CE2_N */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_35, BCM2835_GPIO_FSEL_INPT);	/* SPI1_MISO */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_38, BCM2835_GPIO_FSEL_INPT);	/* SPI1_MOSI */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_40, BCM2835_GPIO_FSEL_INPT);	/* SPI1_SCLK */
+}
+
+#define DIV_ROUND_UP(n,d)	(((n) + (d) - 1) / (d))
+
+uint16_t bcm2835_aux_spi_CalcClockDivider(uint32_t speed_hz)
+{
+    uint16_t divider;
+
+    if (speed_hz < (uint32_t) BCM2835_AUX_SPI_CLOCK_MIN) {
+	speed_hz = (uint32_t) BCM2835_AUX_SPI_CLOCK_MIN;
+    } else if (speed_hz > (uint32_t) BCM2835_AUX_SPI_CLOCK_MAX) {
+	speed_hz = (uint32_t) BCM2835_AUX_SPI_CLOCK_MAX;
+    }
+
+    divider = (uint16_t) DIV_ROUND_UP(BCM2835_CORE_CLK_HZ, 2 * speed_hz) - 1;
+
+    if (divider > (uint16_t) BCM2835_AUX_SPI_CNTL0_SPEED_MAX) {
+	return (uint16_t) BCM2835_AUX_SPI_CNTL0_SPEED_MAX;
+    }
+
+    return divider;
+}
+
+static uint32_t spi1_speed;
+
+void bcm2835_aux_spi_setClockDivider(uint16_t divider)
+{
+    spi1_speed = (uint32_t) divider;
+}
+
+void bcm2835_aux_spi_write(uint16_t data)
+{
+    volatile uint32_t* cntl0 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL0/4;
+    volatile uint32_t* cntl1 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL1/4;
+    volatile uint32_t* stat = bcm2835_spi1 + BCM2835_AUX_SPI_STAT/4;
+    volatile uint32_t* io = bcm2835_spi1 + BCM2835_AUX_SPI_IO/4;
+
+    uint32_t _cntl0 = (spi1_speed << BCM2835_AUX_SPI_CNTL0_SPEED_SHIFT);
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_CS2_N;
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_ENABLE;
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_MSBF_OUT;
+    _cntl0 |= 16; // Shift length
+
+    bcm2835_peri_write(cntl0, _cntl0);
+    bcm2835_peri_write(cntl1, BCM2835_AUX_SPI_CNTL1_MSBF_IN);
+
+    while (bcm2835_peri_read(stat) & BCM2835_AUX_SPI_STAT_TX_FULL)
+	;
+
+    bcm2835_peri_write(io, (uint32_t) data << 16);
+}
+
+void bcm2835_aux_spi_writenb(const char *tbuf, uint32_t len) {
+    volatile uint32_t* cntl0 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL0/4;
+    volatile uint32_t* cntl1 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL1/4;
+    volatile uint32_t* stat = bcm2835_spi1 + BCM2835_AUX_SPI_STAT/4;
+    volatile uint32_t* txhold = bcm2835_spi1 + BCM2835_AUX_SPI_TXHOLD/4;
+    volatile uint32_t* io = bcm2835_spi1 + BCM2835_AUX_SPI_IO/4;
+
+    char *tx = (char *) tbuf;
+    uint32_t tx_len = len;
+    uint32_t count;
+    uint32_t data;
+    uint32_t i;
+    uint8_t byte;
+
+    uint32_t _cntl0 = (spi1_speed << BCM2835_AUX_SPI_CNTL0_SPEED_SHIFT);
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_CS2_N;
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_ENABLE;
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_MSBF_OUT;
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_VAR_WIDTH;
+
+    bcm2835_peri_write(cntl0, _cntl0);
+    bcm2835_peri_write(cntl1, BCM2835_AUX_SPI_CNTL1_MSBF_IN);
+
+    while (tx_len > 0) {
+
+	while (bcm2835_peri_read(stat) & BCM2835_AUX_SPI_STAT_TX_FULL)
+	    ;
+
+	count = MIN(tx_len, 3);
+	data = 0;
+
+	for (i = 0; i < count; i++) {
+	    byte = (tx != NULL) ? (uint8_t) *tx++ : (uint8_t) 0;
+	    data |= byte << (8 * (2 - i));
+	}
+
+	data |= (count * 8) << 24;
+	tx_len -= count;
+
+	if (tx_len != 0) {
+	    bcm2835_peri_write(txhold, data);
+	} else {
+	    bcm2835_peri_write(io, data);
+	}
+
+	while (bcm2835_peri_read(stat) & BCM2835_AUX_SPI_STAT_BUSY)
+	    ;
+
+	(void) bcm2835_peri_read(io);
+    }
+}
+
+void bcm2835_aux_spi_transfernb(const char *tbuf, char *rbuf, uint32_t len) {
+    volatile uint32_t* cntl0 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL0/4;
+    volatile uint32_t* cntl1 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL1/4;
+    volatile uint32_t* stat = bcm2835_spi1 + BCM2835_AUX_SPI_STAT/4;
+    volatile uint32_t* txhold = bcm2835_spi1 + BCM2835_AUX_SPI_TXHOLD/4;
+    volatile uint32_t* io = bcm2835_spi1 + BCM2835_AUX_SPI_IO/4;
+
+	char *tx = (char *)tbuf;
+	char *rx = (char *)rbuf;
+	uint32_t tx_len = len;
+	uint32_t rx_len = len;
+	uint32_t count;
+	uint32_t data;
+	uint32_t i;
+	uint8_t byte;
+
+	uint32_t _cntl0 = (spi1_speed << BCM2835_AUX_SPI_CNTL0_SPEED_SHIFT);
+	_cntl0 |= BCM2835_AUX_SPI_CNTL0_CS2_N;
+	_cntl0 |= BCM2835_AUX_SPI_CNTL0_ENABLE;
+	_cntl0 |= BCM2835_AUX_SPI_CNTL0_MSBF_OUT;
+	_cntl0 |= BCM2835_AUX_SPI_CNTL0_VAR_WIDTH;
+
+	bcm2835_peri_write(cntl0, _cntl0);
+	bcm2835_peri_write(cntl1, BCM2835_AUX_SPI_CNTL1_MSBF_IN);
+
+	while ((tx_len > 0) || (rx_len > 0)) {
+
+		while (!(bcm2835_peri_read(stat) & BCM2835_AUX_SPI_STAT_TX_FULL) && (tx_len > 0)) {
+			count = MIN(tx_len, 3);
+			data = 0;
+
+			for (i = 0; i < count; i++) {
+				byte = (tx != NULL) ? (uint8_t) *tx++ : (uint8_t) 0;
+				data |= byte << (8 * (2 - i));
+			}
+
+			data |= (count * 8) << 24;
+			tx_len -= count;
+
+			if (tx_len != 0) {
+				bcm2835_peri_write(txhold, data);
+			} else {
+				bcm2835_peri_write(io, data);
+			}
+
+		}
+
+		while (!(bcm2835_peri_read(stat) & BCM2835_AUX_SPI_STAT_RX_EMPTY) && (rx_len > 0)) {
+			count = MIN(rx_len, 3);
+			data = bcm2835_peri_read(io);
+
+			if (rbuf != NULL) {
+				switch (count) {
+				case 3:
+					*rx++ = (char)((data >> 16) & 0xFF);
+					/*@fallthrough@*/
+					/* no break */
+				case 2:
+					*rx++ = (char)((data >> 8) & 0xFF);
+					/*@fallthrough@*/
+					/* no break */
+				case 1:
+					*rx++ = (char)((data >> 0) & 0xFF);
+				}
+			}
+
+			rx_len -= count;
+		}
+
+		while (!(bcm2835_peri_read(stat) & BCM2835_AUX_SPI_STAT_BUSY) && (rx_len > 0)) {
+			count = MIN(rx_len, 3);
+			data = bcm2835_peri_read(io);
+
+			if (rbuf != NULL) {
+				switch (count) {
+				case 3:
+					*rx++ = (char)((data >> 16) & 0xFF);
+					/*@fallthrough@*/
+					/* no break */
+				case 2:
+					*rx++ = (char)((data >> 8) & 0xFF);
+					/*@fallthrough@*/
+					/* no break */
+				case 1:
+					*rx++ = (char)((data >> 0) & 0xFF);
+				}
+			}
+
+			rx_len -= count;
+		}
+	}
+}
+
+void bcm2835_aux_spi_transfern(char *buf, uint32_t len) {
+	bcm2835_aux_spi_transfernb(buf, buf, len);
+}
+
+/* Writes (and reads) a single byte to AUX SPI */
+uint8_t bcm2835_aux_spi_transfer(uint8_t value)
+{
+    volatile uint32_t* cntl0 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL0/4;
+    volatile uint32_t* cntl1 = bcm2835_spi1 + BCM2835_AUX_SPI_CNTL1/4;
+    volatile uint32_t* stat = bcm2835_spi1 + BCM2835_AUX_SPI_STAT/4;
+    volatile uint32_t* io = bcm2835_spi1 + BCM2835_AUX_SPI_IO/4;
+
+    uint32_t data;
+
+    uint32_t _cntl0 = (spi1_speed << BCM2835_AUX_SPI_CNTL0_SPEED_SHIFT);
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_CS2_N;
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_ENABLE;
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_MSBF_OUT;
+    _cntl0 |= BCM2835_AUX_SPI_CNTL0_CPHA_IN;
+    _cntl0 |= 8; // Shift length.
+
+    uint32_t _cntl1 = BCM2835_AUX_SPI_CNTL1_MSBF_IN;
+
+    bcm2835_peri_write(cntl1, _cntl1);
+    bcm2835_peri_write(cntl0, _cntl0);
+
+    bcm2835_peri_write(io, (uint32_t) bcm2835_correct_order(value) << 24);
+
+    while (bcm2835_peri_read(stat) & BCM2835_AUX_SPI_STAT_BUSY)
+        ;
+
+    data = bcm2835_correct_order(bcm2835_peri_read(io) & 0xff);
+
+    bcm2835_aux_spi_reset();
+
+    return data;
+}
+
+
+int bcm2835_i2c_begin(void)
+{
+    uint16_t cdiv;
+
+    if (   bcm2835_bsc0 == MAP_FAILED
+	|| bcm2835_bsc1 == MAP_FAILED)
+      return 0; /* bcm2835_init() failed, or not root */
+
+#ifdef I2C_V1
+    volatile uint32_t* paddr = bcm2835_bsc0 + BCM2835_BSC_DIV/4;
+    /* Set the I2C/BSC0 pins to the Alt 0 function to enable I2C access on them */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_03, BCM2835_GPIO_FSEL_ALT0); /* SDA */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_05, BCM2835_GPIO_FSEL_ALT0); /* SCL */
+#else
+    volatile uint32_t* paddr = bcm2835_bsc1 + BCM2835_BSC_DIV/4;
+    /* Set the I2C/BSC1 pins to the Alt 0 function to enable I2C access on them */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_03, BCM2835_GPIO_FSEL_ALT0); /* SDA */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_05, BCM2835_GPIO_FSEL_ALT0); /* SCL */
+#endif    
+
+    /* Read the clock divider register */
+    cdiv = bcm2835_peri_read(paddr);
+    /* Calculate time for transmitting one byte
+    // 1000000 = micros seconds in a second
+    // 9 = Clocks per byte : 8 bits + ACK
+    */
+    i2c_byte_wait_us = ((float)cdiv / BCM2835_CORE_CLK_HZ) * 1000000 * 9;
+
+    return 1;
+}
+
+void bcm2835_i2c_end(void)
+{
+#ifdef I2C_V1
+    /* Set all the I2C/BSC0 pins back to input */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_03, BCM2835_GPIO_FSEL_INPT); /* SDA */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_05, BCM2835_GPIO_FSEL_INPT); /* SCL */
+#else
+    /* Set all the I2C/BSC1 pins back to input */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_03, BCM2835_GPIO_FSEL_INPT); /* SDA */
+    bcm2835_gpio_fsel(RPI_V2_GPIO_P1_05, BCM2835_GPIO_FSEL_INPT); /* SCL */
+#endif
+}
+
+void bcm2835_i2c_setSlaveAddress(uint8_t addr)
+{
+    /* Set I2C Device Address */
+#ifdef I2C_V1
+    volatile uint32_t* paddr = bcm2835_bsc0 + BCM2835_BSC_A/4;
+#else	
+    volatile uint32_t* paddr = bcm2835_bsc1 + BCM2835_BSC_A/4;
+#endif
+    bcm2835_peri_write(paddr, addr);
+}
+
+/* defaults to 0x5dc, should result in a 166.666 kHz I2C clock frequency.
+// The divisor must be a power of 2. Odd numbers
+// rounded down.
+*/
+void bcm2835_i2c_setClockDivider(uint16_t divider)
+{
+#ifdef I2C_V1
+    volatile uint32_t* paddr = bcm2835_bsc0 + BCM2835_BSC_DIV/4;
+#else
+    volatile uint32_t* paddr = bcm2835_bsc1 + BCM2835_BSC_DIV/4;
+#endif    
+    bcm2835_peri_write(paddr, divider);
+    /* Calculate time for transmitting one byte
+    // 1000000 = micros seconds in a second
+    // 9 = Clocks per byte : 8 bits + ACK
+    */
+    i2c_byte_wait_us = ((float)divider / BCM2835_CORE_CLK_HZ) * 1000000 * 9;
+}
+
+/* set I2C clock divider by means of a baudrate number */
+void bcm2835_i2c_set_baudrate(uint32_t baudrate)
+{
+	uint32_t divider;
+	/* use 0xFFFE mask to limit a max value and round down any odd number */
+	divider = (BCM2835_CORE_CLK_HZ / baudrate) & 0xFFFE;
+	bcm2835_i2c_setClockDivider( (uint16_t)divider );
+}
+
+/* Writes an number of bytes to I2C */
+uint8_t bcm2835_i2c_write(const char * buf, uint32_t len)
+{
+#ifdef I2C_V1
+    volatile uint32_t* dlen    = bcm2835_bsc0 + BCM2835_BSC_DLEN/4;
+    volatile uint32_t* fifo    = bcm2835_bsc0 + BCM2835_BSC_FIFO/4;
+    volatile uint32_t* status  = bcm2835_bsc0 + BCM2835_BSC_S/4;
+    volatile uint32_t* control = bcm2835_bsc0 + BCM2835_BSC_C/4;
+#else
+    volatile uint32_t* dlen    = bcm2835_bsc1 + BCM2835_BSC_DLEN/4;
+    volatile uint32_t* fifo    = bcm2835_bsc1 + BCM2835_BSC_FIFO/4;
+    volatile uint32_t* status  = bcm2835_bsc1 + BCM2835_BSC_S/4;
+    volatile uint32_t* control = bcm2835_bsc1 + BCM2835_BSC_C/4;
+#endif    
+
+    uint32_t remaining = len;
+    uint32_t i = 0;
+    uint8_t reason = BCM2835_I2C_REASON_OK;
+
+    /* Clear FIFO */
+    bcm2835_peri_set_bits(control, BCM2835_BSC_C_CLEAR_1 , BCM2835_BSC_C_CLEAR_1 );
+    /* Clear Status */
+    bcm2835_peri_write(status, BCM2835_BSC_S_CLKT | BCM2835_BSC_S_ERR | BCM2835_BSC_S_DONE);
+    /* Set Data Length */
+    bcm2835_peri_write(dlen, len);
+    /* pre populate FIFO with max buffer */
+    while( remaining && ( i < BCM2835_BSC_FIFO_SIZE ) )
+    {
+        bcm2835_peri_write_nb(fifo, buf[i]);
+        i++;
+        remaining--;
+    }
+    
+    /* Enable device and start transfer */
+    bcm2835_peri_write(control, BCM2835_BSC_C_I2CEN | BCM2835_BSC_C_ST);
+    
+    /* Transfer is over when BCM2835_BSC_S_DONE */
+    while(!(bcm2835_peri_read(status) & BCM2835_BSC_S_DONE ))
+    {
+        while ( remaining && (bcm2835_peri_read(status) & BCM2835_BSC_S_TXD ))
+    	{
+	    /* Write to FIFO */
+	    bcm2835_peri_write(fifo, buf[i]);
+	    i++;
+	    remaining--;
+    	}
+    }
+
+    /* Received a NACK */
+    if (bcm2835_peri_read(status) & BCM2835_BSC_S_ERR)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_NACK;
+    }
+
+    /* Received Clock Stretch Timeout */
+    else if (bcm2835_peri_read(status) & BCM2835_BSC_S_CLKT)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_CLKT;
+    }
+
+    /* Not all data is sent */
+    else if (remaining)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_DATA;
+    }
+
+    bcm2835_peri_set_bits(control, BCM2835_BSC_S_DONE , BCM2835_BSC_S_DONE);
+
+    return reason;
+}
+
+/* Read an number of bytes from I2C */
+uint8_t bcm2835_i2c_read(char* buf, uint32_t len)
+{
+#ifdef I2C_V1
+    volatile uint32_t* dlen    = bcm2835_bsc0 + BCM2835_BSC_DLEN/4;
+    volatile uint32_t* fifo    = bcm2835_bsc0 + BCM2835_BSC_FIFO/4;
+    volatile uint32_t* status  = bcm2835_bsc0 + BCM2835_BSC_S/4;
+    volatile uint32_t* control = bcm2835_bsc0 + BCM2835_BSC_C/4;
+#else
+    volatile uint32_t* dlen    = bcm2835_bsc1 + BCM2835_BSC_DLEN/4;
+    volatile uint32_t* fifo    = bcm2835_bsc1 + BCM2835_BSC_FIFO/4;
+    volatile uint32_t* status  = bcm2835_bsc1 + BCM2835_BSC_S/4;
+    volatile uint32_t* control = bcm2835_bsc1 + BCM2835_BSC_C/4;
+#endif    
+
+    uint32_t remaining = len;
+    uint32_t i = 0;
+    uint8_t reason = BCM2835_I2C_REASON_OK;
+
+    /* Clear FIFO */
+    bcm2835_peri_set_bits(control, BCM2835_BSC_C_CLEAR_1 , BCM2835_BSC_C_CLEAR_1 );
+    /* Clear Status */
+    bcm2835_peri_write_nb(status, BCM2835_BSC_S_CLKT | BCM2835_BSC_S_ERR | BCM2835_BSC_S_DONE);
+    /* Set Data Length */
+    bcm2835_peri_write_nb(dlen, len);
+    /* Start read */
+    bcm2835_peri_write_nb(control, BCM2835_BSC_C_I2CEN | BCM2835_BSC_C_ST | BCM2835_BSC_C_READ);
+    
+    /* wait for transfer to complete */
+    while (!(bcm2835_peri_read_nb(status) & BCM2835_BSC_S_DONE))
+    {
+        /* we must empty the FIFO as it is populated and not use any delay */
+        while (remaining && bcm2835_peri_read_nb(status) & BCM2835_BSC_S_RXD)
+    	{
+	    /* Read from FIFO, no barrier */
+	    buf[i] = bcm2835_peri_read_nb(fifo);
+	    i++;
+	    remaining--;
+    	}
+    }
+    
+    /* transfer has finished - grab any remaining stuff in FIFO */
+    while (remaining && (bcm2835_peri_read_nb(status) & BCM2835_BSC_S_RXD))
+    {
+        /* Read from FIFO, no barrier */
+        buf[i] = bcm2835_peri_read_nb(fifo);
+        i++;
+        remaining--;
+    }
+    
+    /* Received a NACK */
+    if (bcm2835_peri_read(status) & BCM2835_BSC_S_ERR)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_NACK;
+    }
+
+    /* Received Clock Stretch Timeout */
+    else if (bcm2835_peri_read(status) & BCM2835_BSC_S_CLKT)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_CLKT;
+    }
+
+    /* Not all data is received */
+    else if (remaining)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_DATA;
+    }
+
+    bcm2835_peri_set_bits(status, BCM2835_BSC_S_DONE , BCM2835_BSC_S_DONE);
+
+    return reason;
+}
+
+/* Read an number of bytes from I2C sending a repeated start after writing
+// the required register. Only works if your device supports this mode
+*/
+uint8_t bcm2835_i2c_read_register_rs(char* regaddr, char* buf, uint32_t len)
+{   
+#ifdef I2C_V1
+    volatile uint32_t* dlen    = bcm2835_bsc0 + BCM2835_BSC_DLEN/4;
+    volatile uint32_t* fifo    = bcm2835_bsc0 + BCM2835_BSC_FIFO/4;
+    volatile uint32_t* status  = bcm2835_bsc0 + BCM2835_BSC_S/4;
+    volatile uint32_t* control = bcm2835_bsc0 + BCM2835_BSC_C/4;
+#else
+    volatile uint32_t* dlen    = bcm2835_bsc1 + BCM2835_BSC_DLEN/4;
+    volatile uint32_t* fifo    = bcm2835_bsc1 + BCM2835_BSC_FIFO/4;
+    volatile uint32_t* status  = bcm2835_bsc1 + BCM2835_BSC_S/4;
+    volatile uint32_t* control = bcm2835_bsc1 + BCM2835_BSC_C/4;
+#endif    
+	uint32_t remaining = len;
+    uint32_t i = 0;
+    uint8_t reason = BCM2835_I2C_REASON_OK;
+    
+    /* Clear FIFO */
+    bcm2835_peri_set_bits(control, BCM2835_BSC_C_CLEAR_1 , BCM2835_BSC_C_CLEAR_1 );
+    /* Clear Status */
+    bcm2835_peri_write(status, BCM2835_BSC_S_CLKT | BCM2835_BSC_S_ERR | BCM2835_BSC_S_DONE);
+    /* Set Data Length */
+    bcm2835_peri_write(dlen, 1);
+    /* Enable device and start transfer */
+    bcm2835_peri_write(control, BCM2835_BSC_C_I2CEN);
+    bcm2835_peri_write(fifo, regaddr[0]);
+    bcm2835_peri_write(control, BCM2835_BSC_C_I2CEN | BCM2835_BSC_C_ST);
+    
+    /* poll for transfer has started */
+    while ( !( bcm2835_peri_read(status) & BCM2835_BSC_S_TA ) )
+    {
+        /* Linux may cause us to miss entire transfer stage */
+        if(bcm2835_peri_read(status) & BCM2835_BSC_S_DONE)
+            break;
+    }
+    
+    /* Send a repeated start with read bit set in address */
+    bcm2835_peri_write(dlen, len);
+    bcm2835_peri_write(control, BCM2835_BSC_C_I2CEN | BCM2835_BSC_C_ST  | BCM2835_BSC_C_READ );
+    
+    /* Wait for write to complete and first byte back. */
+    bcm2835_delayMicroseconds(i2c_byte_wait_us * 3);
+    
+    /* wait for transfer to complete */
+    while (!(bcm2835_peri_read(status) & BCM2835_BSC_S_DONE))
+    {
+        /* we must empty the FIFO as it is populated and not use any delay */
+        while (remaining && bcm2835_peri_read(status) & BCM2835_BSC_S_RXD)
+    	{
+	    /* Read from FIFO */
+	    buf[i] = bcm2835_peri_read(fifo);
+	    i++;
+	    remaining--;
+    	}
+    }
+    
+    /* transfer has finished - grab any remaining stuff in FIFO */
+    while (remaining && (bcm2835_peri_read(status) & BCM2835_BSC_S_RXD))
+    {
+        /* Read from FIFO */
+        buf[i] = bcm2835_peri_read(fifo);
+        i++;
+        remaining--;
+    }
+    
+    /* Received a NACK */
+    if (bcm2835_peri_read(status) & BCM2835_BSC_S_ERR)
+    {
+		reason = BCM2835_I2C_REASON_ERROR_NACK;
+    }
+
+    /* Received Clock Stretch Timeout */
+    else if (bcm2835_peri_read(status) & BCM2835_BSC_S_CLKT)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_CLKT;
+    }
+
+    /* Not all data is sent */
+    else if (remaining)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_DATA;
+    }
+
+    bcm2835_peri_set_bits(control, BCM2835_BSC_S_DONE , BCM2835_BSC_S_DONE);
+
+    return reason;
+}
+
+/* Sending an arbitrary number of bytes before issuing a repeated start 
+// (with no prior stop) and reading a response. Some devices require this behavior.
+*/
+uint8_t bcm2835_i2c_write_read_rs(char* cmds, uint32_t cmds_len, char* buf, uint32_t buf_len)
+{   
+#ifdef I2C_V1
+    volatile uint32_t* dlen    = bcm2835_bsc0 + BCM2835_BSC_DLEN/4;
+    volatile uint32_t* fifo    = bcm2835_bsc0 + BCM2835_BSC_FIFO/4;
+    volatile uint32_t* status  = bcm2835_bsc0 + BCM2835_BSC_S/4;
+    volatile uint32_t* control = bcm2835_bsc0 + BCM2835_BSC_C/4;
+#else
+    volatile uint32_t* dlen    = bcm2835_bsc1 + BCM2835_BSC_DLEN/4;
+    volatile uint32_t* fifo    = bcm2835_bsc1 + BCM2835_BSC_FIFO/4;
+    volatile uint32_t* status  = bcm2835_bsc1 + BCM2835_BSC_S/4;
+    volatile uint32_t* control = bcm2835_bsc1 + BCM2835_BSC_C/4;
+#endif    
+
+    uint32_t remaining = cmds_len;
+    uint32_t i = 0;
+    uint8_t reason = BCM2835_I2C_REASON_OK;
+    
+    /* Clear FIFO */
+    bcm2835_peri_set_bits(control, BCM2835_BSC_C_CLEAR_1 , BCM2835_BSC_C_CLEAR_1 );
+
+    /* Clear Status */
+    bcm2835_peri_write(status, BCM2835_BSC_S_CLKT | BCM2835_BSC_S_ERR | BCM2835_BSC_S_DONE);
+
+    /* Set Data Length */
+    bcm2835_peri_write(dlen, cmds_len);
+ 
+    /* pre populate FIFO with max buffer */
+    while( remaining && ( i < BCM2835_BSC_FIFO_SIZE ) )
+    {
+        bcm2835_peri_write_nb(fifo, cmds[i]);
+        i++;
+        remaining--;
+    }
+
+    /* Enable device and start transfer */
+    bcm2835_peri_write(control, BCM2835_BSC_C_I2CEN | BCM2835_BSC_C_ST);
+    
+    /* poll for transfer has started (way to do repeated start, from BCM2835 datasheet) */
+    while ( !( bcm2835_peri_read(status) & BCM2835_BSC_S_TA ) )
+    {
+        /* Linux may cause us to miss entire transfer stage */
+        if(bcm2835_peri_read_nb(status) & BCM2835_BSC_S_DONE)
+            break;
+    }
+    
+    remaining = buf_len;
+    i = 0;
+
+    /* Send a repeated start with read bit set in address */
+    bcm2835_peri_write(dlen, buf_len);
+    bcm2835_peri_write(control, BCM2835_BSC_C_I2CEN | BCM2835_BSC_C_ST  | BCM2835_BSC_C_READ );
+    
+    /* Wait for write to complete and first byte back. */
+    bcm2835_delayMicroseconds(i2c_byte_wait_us * (cmds_len + 1));
+    
+    /* wait for transfer to complete */
+    while (!(bcm2835_peri_read_nb(status) & BCM2835_BSC_S_DONE))
+    {
+        /* we must empty the FIFO as it is populated and not use any delay */
+        while (remaining && bcm2835_peri_read(status) & BCM2835_BSC_S_RXD)
+    	{
+	    /* Read from FIFO, no barrier */
+	    buf[i] = bcm2835_peri_read_nb(fifo);
+	    i++;
+	    remaining--;
+    	}
+    }
+    
+    /* transfer has finished - grab any remaining stuff in FIFO */
+    while (remaining && (bcm2835_peri_read(status) & BCM2835_BSC_S_RXD))
+    {
+        /* Read from FIFO */
+        buf[i] = bcm2835_peri_read(fifo);
+        i++;
+        remaining--;
+    }
+    
+    /* Received a NACK */
+    if (bcm2835_peri_read(status) & BCM2835_BSC_S_ERR)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_NACK;
+    }
+
+    /* Received Clock Stretch Timeout */
+    else if (bcm2835_peri_read(status) & BCM2835_BSC_S_CLKT)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_CLKT;
+    }
+
+    /* Not all data is sent */
+    else if (remaining)
+    {
+	reason = BCM2835_I2C_REASON_ERROR_DATA;
+    }
+
+    bcm2835_peri_set_bits(control, BCM2835_BSC_S_DONE , BCM2835_BSC_S_DONE);
+
+    return reason;
+}
+
+/* Read the System Timer Counter (64-bits) */
+uint64_t bcm2835_st_read(void)
+{
+    volatile uint32_t* paddr;
+    uint32_t hi, lo;
+    uint64_t st;
+
+    if (bcm2835_st==MAP_FAILED)
+	return 0;
+
+    paddr = bcm2835_st + BCM2835_ST_CHI/4;
+    hi = bcm2835_peri_read(paddr);
+
+    paddr = bcm2835_st + BCM2835_ST_CLO/4;
+    lo = bcm2835_peri_read(paddr);
+    
+    paddr = bcm2835_st + BCM2835_ST_CHI/4;
+    st = bcm2835_peri_read(paddr);
+    
+    /* Test for overflow */
+    if (st == hi)
+    {
+        st <<= 32;
+        st += lo;
+    }
+    else
+    {
+        st <<= 32;
+        paddr = bcm2835_st + BCM2835_ST_CLO/4;
+        st += bcm2835_peri_read(paddr);
+    }
+    return st;
+}
+
+/* Delays for the specified number of microseconds with offset */
+void bcm2835_st_delay(uint64_t offset_micros, uint64_t micros)
+{
+    uint64_t compare = offset_micros + micros;
+
+    while(bcm2835_st_read() < compare)
+	;
+}
+
+/* PWM */
+
+void bcm2835_pwm_set_clock(uint32_t divisor)
+{
+    if (   bcm2835_clk == MAP_FAILED
+        || bcm2835_pwm == MAP_FAILED)
+      return; /* bcm2835_init() failed or not root */
+  
+    /* From Gerts code */
+    divisor &= 0xfff;
+    /* Stop PWM clock */
+    bcm2835_peri_write(bcm2835_clk + BCM2835_PWMCLK_CNTL, BCM2835_PWM_PASSWRD | 0x01);
+    bcm2835_delay(110); /* Prevents clock going slow */
+    /* Wait for the clock to be not busy */
+    while ((bcm2835_peri_read(bcm2835_clk + BCM2835_PWMCLK_CNTL) & 0x80) != 0)
+	bcm2835_delay(1); 
+    /* set the clock divider and enable PWM clock */
+    bcm2835_peri_write(bcm2835_clk + BCM2835_PWMCLK_DIV, BCM2835_PWM_PASSWRD | (divisor << 12));
+    bcm2835_peri_write(bcm2835_clk + BCM2835_PWMCLK_CNTL, BCM2835_PWM_PASSWRD | 0x11); /* Source=osc and enable */
+}
+
+void bcm2835_pwm_set_mode(uint8_t channel, uint8_t markspace, uint8_t enabled)
+{
+  if (   bcm2835_clk == MAP_FAILED
+       || bcm2835_pwm == MAP_FAILED)
+    return; /* bcm2835_init() failed or not root */
+
+  uint32_t control = bcm2835_peri_read(bcm2835_pwm + BCM2835_PWM_CONTROL);
+
+  if (channel == 0)
+    {
+      if (markspace)
+	control |= BCM2835_PWM0_MS_MODE;
+      else
+	control &= ~BCM2835_PWM0_MS_MODE;
+      if (enabled)
+	control |= BCM2835_PWM0_ENABLE;
+      else
+	control &= ~BCM2835_PWM0_ENABLE;
+    }
+  else if (channel == 1)
+    {
+      if (markspace)
+	control |= BCM2835_PWM1_MS_MODE;
+      else
+	control &= ~BCM2835_PWM1_MS_MODE;
+      if (enabled)
+	control |= BCM2835_PWM1_ENABLE;
+      else
+	control &= ~BCM2835_PWM1_ENABLE;
+    }
+
+  /* If you use the barrier here, wierd things happen, and the commands dont work */
+  bcm2835_peri_write_nb(bcm2835_pwm + BCM2835_PWM_CONTROL, control);
+  /*  bcm2835_peri_write_nb(bcm2835_pwm + BCM2835_PWM_CONTROL, BCM2835_PWM0_ENABLE | BCM2835_PWM1_ENABLE | BCM2835_PWM0_MS_MODE | BCM2835_PWM1_MS_MODE); */
+
+}
+
+void bcm2835_pwm_set_range(uint8_t channel, uint32_t range)
+{
+  if (   bcm2835_clk == MAP_FAILED
+       || bcm2835_pwm == MAP_FAILED)
+    return; /* bcm2835_init() failed or not root */
+
+  if (channel == 0)
+      bcm2835_peri_write_nb(bcm2835_pwm + BCM2835_PWM0_RANGE, range);
+  else if (channel == 1)
+      bcm2835_peri_write_nb(bcm2835_pwm + BCM2835_PWM1_RANGE, range);
+}
+
+void bcm2835_pwm_set_data(uint8_t channel, uint32_t data)
+{
+  if (   bcm2835_clk == MAP_FAILED
+       || bcm2835_pwm == MAP_FAILED)
+    return; /* bcm2835_init() failed or not root */
+
+  if (channel == 0)
+      bcm2835_peri_write_nb(bcm2835_pwm + BCM2835_PWM0_DATA, data);
+  else if (channel == 1)
+      bcm2835_peri_write_nb(bcm2835_pwm + BCM2835_PWM1_DATA, data);
+}
+
+/* Allocate page-aligned memory. */
+void *malloc_aligned(size_t size)
+{
+    void *mem;
+    errno = posix_memalign(&mem, BCM2835_PAGE_SIZE, size);
+    return (errno ? NULL : mem);
+}
+
+/* Map 'size' bytes starting at 'off' in file 'fd' to memory.
+// Return mapped address on success, MAP_FAILED otherwise.
+// On error print message.
+*/
+static void *mapmem(const char *msg, size_t size, int fd, off_t off)
+{
+    void *map = mmap(NULL, size, (PROT_READ | PROT_WRITE), MAP_SHARED, fd, off);
+    if (map == MAP_FAILED)
+	fprintf(stderr, "bcm2835_init: %s mmap failed: %s\n", msg, strerror(errno));
+    return map;
+}
+
+static void unmapmem(void **pmem, size_t size)
+{
+    if (*pmem == MAP_FAILED) return;
+    munmap(*pmem, size);
+    *pmem = MAP_FAILED;
+}
+
+/* Initialise this library. */
+int bcm2835_init(void)
+{
+    int  memfd;
+    int  ok;
+    FILE *fp;
+
+    if (debug) 
+    {
+        bcm2835_peripherals = (uint32_t*)BCM2835_PERI_BASE;
+
+	bcm2835_pads = bcm2835_peripherals + BCM2835_GPIO_PADS/4;
+	bcm2835_clk  = bcm2835_peripherals + BCM2835_CLOCK_BASE/4;
+	bcm2835_gpio = bcm2835_peripherals + BCM2835_GPIO_BASE/4;
+	bcm2835_pwm  = bcm2835_peripherals + BCM2835_GPIO_PWM/4;
+	bcm2835_spi0 = bcm2835_peripherals + BCM2835_SPI0_BASE/4;
+	bcm2835_bsc0 = bcm2835_peripherals + BCM2835_BSC0_BASE/4;
+	bcm2835_bsc1 = bcm2835_peripherals + BCM2835_BSC1_BASE/4;
+	bcm2835_st   = bcm2835_peripherals + BCM2835_ST_BASE/4;
+	bcm2835_aux  = bcm2835_peripherals + BCM2835_AUX_BASE/4;
+	bcm2835_spi1 = bcm2835_peripherals + BCM2835_SPI1_BASE/4;
+
+	return 1; /* Success */
+    }
+
+    /* Figure out the base and size of the peripheral address block
+    // using the device-tree. Required for RPi2/3/4, optional for RPi 1
+    */
+    if ((fp = fopen(BMC2835_RPI2_DT_FILENAME , "rb")))
+    {
+        unsigned char buf[16];
+        uint32_t base_address;
+        uint32_t peri_size;
+        if (fread(buf, 1, sizeof(buf), fp) >= 8)
+        {
+            base_address = (buf[4] << 24) |
+              (buf[5] << 16) |
+              (buf[6] << 8) |
+              (buf[7] << 0);
+            
+            peri_size = (buf[8] << 24) |
+              (buf[9] << 16) |
+              (buf[10] << 8) |
+              (buf[11] << 0);
+            
+            if (!base_address)
+            {
+                /* looks like RPI 4 */
+                base_address = (buf[8] << 24) |
+                      (buf[9] << 16) |
+                      (buf[10] << 8) |
+                      (buf[11] << 0);
+                      
+                peri_size = (buf[12] << 24) |
+                (buf[13] << 16) |
+                (buf[14] << 8) |
+                (buf[15] << 0);
+            }
+            /* check for valid known range formats */
+            if ((buf[0] == 0x7e) &&
+                    (buf[1] == 0x00) &&
+                    (buf[2] == 0x00) &&
+                    (buf[3] == 0x00) &&
+                    ((base_address == BCM2835_PERI_BASE) || (base_address == BCM2835_RPI2_PERI_BASE) || (base_address == BCM2835_RPI4_PERI_BASE)))
+            {
+                bcm2835_peripherals_base = (off_t)base_address;
+                bcm2835_peripherals_size = (size_t)peri_size;
+                if( base_address == BCM2835_RPI4_PERI_BASE )
+                {
+                    pud_type_rpi4 = 1;
+                }
+            }
+        
+        }
+        
+	fclose(fp);
+    }
+    /* else we are prob on RPi 1 with BCM2835, and use the hardwired defaults */
+
+    /* Now get ready to map the peripherals block 
+     * If we are not root, try for the new /dev/gpiomem interface and accept
+     * the fact that we can only access GPIO
+     * else try for the /dev/mem interface and get access to everything
+     */
+    memfd = -1;
+    ok = 0;
+    if (geteuid() == 0
+#ifdef BCM2835_HAVE_LIBCAP
+	|| bcm2835_has_capability(CAP_SYS_RAWIO)
+#endif
+	)
+    {
+      /* Open the master /dev/mem device */
+      if ((memfd = open("/dev/mem", O_RDWR | O_SYNC) ) < 0) 
+	{
+	  fprintf(stderr, "bcm2835_init: Unable to open /dev/mem: %s\n",
+		  strerror(errno)) ;
+	  goto exit;
+	}
+      
+      /* Base of the peripherals block is mapped to VM */
+      bcm2835_peripherals = mapmem("gpio", bcm2835_peripherals_size, memfd, bcm2835_peripherals_base);
+      if (bcm2835_peripherals == MAP_FAILED) goto exit;
+      
+      /* Now compute the base addresses of various peripherals, 
+      // which are at fixed offsets within the mapped peripherals block
+      // Caution: bcm2835_peripherals is uint32_t*, so divide offsets by 4
+      */
+      bcm2835_gpio = bcm2835_peripherals + BCM2835_GPIO_BASE/4;
+      bcm2835_pwm  = bcm2835_peripherals + BCM2835_GPIO_PWM/4;
+      bcm2835_clk  = bcm2835_peripherals + BCM2835_CLOCK_BASE/4;
+      bcm2835_pads = bcm2835_peripherals + BCM2835_GPIO_PADS/4;
+      bcm2835_spi0 = bcm2835_peripherals + BCM2835_SPI0_BASE/4;
+      bcm2835_bsc0 = bcm2835_peripherals + BCM2835_BSC0_BASE/4; /* I2C */
+      bcm2835_bsc1 = bcm2835_peripherals + BCM2835_BSC1_BASE/4; /* I2C */
+      bcm2835_st   = bcm2835_peripherals + BCM2835_ST_BASE/4;
+      bcm2835_aux  = bcm2835_peripherals + BCM2835_AUX_BASE/4;
+      bcm2835_spi1 = bcm2835_peripherals + BCM2835_SPI1_BASE/4;
+
+      ok = 1;
+    }
+    else
+    {
+      /* Not root, try /dev/gpiomem */
+      /* Open the master /dev/mem device */
+      if ((memfd = open("/dev/gpiomem", O_RDWR | O_SYNC) ) < 0) 
+	{
+	  fprintf(stderr, "bcm2835_init: Unable to open /dev/gpiomem: %s\n",
+		  strerror(errno)) ;
+	  goto exit;
+	}
+      
+      /* Base of the peripherals block is mapped to VM */
+      bcm2835_peripherals_base = 0;
+      bcm2835_peripherals = mapmem("gpio", bcm2835_peripherals_size, memfd, bcm2835_peripherals_base);
+      if (bcm2835_peripherals == MAP_FAILED) goto exit;
+      bcm2835_gpio = bcm2835_peripherals;
+      ok = 1;
+    }
+
+exit:
+    if (memfd >= 0)
+        close(memfd);
+
+    if (!ok)
+	bcm2835_close();
+
+    return ok;
+}
+
+/* Close this library and deallocate everything */
+int bcm2835_close(void)
+{
+    if (debug) return 1; /* Success */
+
+    unmapmem((void**) &bcm2835_peripherals, bcm2835_peripherals_size);
+    bcm2835_peripherals = MAP_FAILED;
+    bcm2835_gpio = MAP_FAILED;
+    bcm2835_pwm  = MAP_FAILED;
+    bcm2835_clk  = MAP_FAILED;
+    bcm2835_pads = MAP_FAILED;
+    bcm2835_spi0 = MAP_FAILED;
+    bcm2835_bsc0 = MAP_FAILED;
+    bcm2835_bsc1 = MAP_FAILED;
+    bcm2835_st   = MAP_FAILED;
+    bcm2835_aux  = MAP_FAILED;
+    bcm2835_spi1 = MAP_FAILED;
+    return 1; /* Success */
+}    
+
+#ifdef BCM2835_TEST
+/* this is a simple test program that prints out what it will do rather than 
+// actually doing it
+*/
+int main(int argc, char **argv)
+{
+    /* Be non-destructive */
+    bcm2835_set_debug(1);
+
+    if (!bcm2835_init())
+	return 1;
+
+    /* Configure some GPIO pins fo some testing
+    // Set RPI pin P1-11 to be an output
+    */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_11, BCM2835_GPIO_FSEL_OUTP);
+    /* Set RPI pin P1-15 to be an input */
+    bcm2835_gpio_fsel(RPI_GPIO_P1_15, BCM2835_GPIO_FSEL_INPT);
+    /*  with a pullup */
+    bcm2835_gpio_set_pud(RPI_GPIO_P1_15, BCM2835_GPIO_PUD_UP);
+    /* And a low detect enable */
+    bcm2835_gpio_len(RPI_GPIO_P1_15);
+    /* and input hysteresis disabled on GPIOs 0 to 27 */
+    bcm2835_gpio_set_pad(BCM2835_PAD_GROUP_GPIO_0_27, BCM2835_PAD_SLEW_RATE_UNLIMITED|BCM2835_PAD_DRIVE_8mA);
+
+#if 1
+    /* Blink */
+    while (1)
+    {
+	/* Turn it on */
+	bcm2835_gpio_write(RPI_GPIO_P1_11, HIGH);
+	
+	/* wait a bit */
+	bcm2835_delay(500);
+	
+	/* turn it off */
+	bcm2835_gpio_write(RPI_GPIO_P1_11, LOW);
+	
+	/* wait a bit */
+	bcm2835_delay(500);
+    }
+#endif
+
+#if 0
+    /* Read input */
+    while (1)
+    {
+	/* Read some data */
+	uint8_t value = bcm2835_gpio_lev(RPI_GPIO_P1_15);
+	printf("read from pin 15: %d\n", value);
+	
+	/* wait a bit */
+	bcm2835_delay(500);
+    }
+#endif
+
+#if 0
+    /* Look for a low event detection
+    // eds will be set whenever pin 15 goes low
+    */
+    while (1)
+    {
+	if (bcm2835_gpio_eds(RPI_GPIO_P1_15))
+	{
+	    /* Now clear the eds flag by setting it to 1 */
+	    bcm2835_gpio_set_eds(RPI_GPIO_P1_15);
+	    printf("low event detect for pin 15\n");
+	}
+
+	/* wait a bit */
+	bcm2835_delay(500);
+    }
+#endif
+
+    if (!bcm2835_close())
+	return 1;
+
+    return 0;
+}
+#endif
+
+
+