bcm2835.c

/* 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 1.23 2015/03/31 04:55:41 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
*/
uint32_t *bcm2835_peripherals_base = (uint32_t *)BCM2835_PERI_BASE;
uint32_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;


/* 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;

/* I2C The time needed to transmit one byte. In microseconds.
 */
static int i2c_byte_wait_us = 0;

/*
// 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;
    }
    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 %08X\n", (unsigned) 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 %08X\n", (unsigned) 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 %08X, value %08X\n", (unsigned) 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 %08X, value %08X\n",
               (unsigned) 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)
{
    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)
{
    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", micros);
	return;
    }

    if(micros < 450) {
	struct timespec spTm;
	int64_t stTm = 0, cTm, toTm = 1000ll*micros;
	while(1) {
	    clock_gettime(CLOCK_MONOTONIC, &spTm);
	    cTm = 1000000000ll*spTm.tv_sec + spTm.tv_nsec;
	    if(!stTm) stTm = cTm;
	    else if((cTm-stTm) >= toTm) break;
	}
    }
    else {
	t1.tv_sec = 0;
	t1.tv_nsec = 1000 * (long)(micros-100);
	nanosleep(&t1, NULL);
    }

    /* 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();
    
    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
*/
void bcm2835_gpio_set_pud(uint8_t pin, uint8_t pud)
{
    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);
}

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 __attribute__((unused)) order)
{
    /* BCM2835_SPI_BIT_ORDER_MSBFIRST is the only one supported by SPI0 */
}

/* 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_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, 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_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, 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_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(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, 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);
}

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 (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(control, 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;
    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;
	return 1; /* Success */
    }

    /* Figure out the base and size of the peripheral address block
    // using the device-tree. Required for RPi2, optional for RPi 1
    */
    if ((fp = fopen(BMC2835_RPI2_DT_FILENAME , "rb")))
    {
        unsigned char buf[4];
	fseek(fp, BMC2835_RPI2_DT_PERI_BASE_ADDRESS_OFFSET, SEEK_SET);
	if (fread(buf, 1, sizeof(buf), fp) == sizeof(buf))
	  bcm2835_peripherals_base = (uint32_t *)(buf[0] << 24 | buf[1] << 16 | buf[2] << 8 | buf[3] << 0);
	fseek(fp, BMC2835_RPI2_DT_PERI_SIZE_OFFSET, SEEK_SET);
	if (fread(buf, 1, sizeof(buf), fp) == sizeof(buf))
	  bcm2835_peripherals_size = (buf[0] << 24 | buf[1] << 16 | buf[2] << 8 | buf[3] << 0);
	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)
    {
      /* 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, (uint32_t)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;
      
      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, (uint32_t)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;
    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