gpio.c

/*
 * gpio.c: the real-time process that handles multiplexing
 * 
 * www.obsolescenceguaranteed.blogspot.com
 * 
 * The only communication with the main program (simh):
 * - external variable ledstatus is read to determine which leds to light.
 * - external variable switchstatus is updated with current switch settings.
 * 
*/


// TO DO: define SERIALSETUP to use PiDPs wired for serial port
//#define SERIALSETUP


#include <time.h>
#include <pthread.h>
#include <stdint.h>
#include "gpio.h"

typedef unsigned int    uint32; 
typedef signed int      int32; 
typedef unsigned short    uint16; 

void short_wait(void);		// used as pause between clocked GPIO changes
unsigned bcm_host_get_peripheral_address(void);		// find Pi 2 or Pi's gpio base address
static unsigned get_dt_ranges(const char *filename, unsigned offset); // Pi 2 detect

struct bcm2835_peripheral gpio;	// needs initialisation

long intervl = 300000;		// light each row of leds this long

uint32 switchstatus[3] = { 0 }; // bitfields: 3 rows of up to 12 switches
uint32 ledstatus[8] = { 0 };	// bitfields: 8 ledrows of up to 12 LEDs

// PART 1 - GPIO and RT process stuff ----------------------------------

// GPIO setup macros. Always use INP_GPIO(x) before using OUT_GPIO(x)
#define INP_GPIO(g)   *(gpio.addr + ((g)/10)) &= ~(7<<(((g)%10)*3))
#define OUT_GPIO(g)   *(gpio.addr + ((g)/10)) |=  (1<<(((g)%10)*3))
#define SET_GPIO_ALT(g,a) *(gpio.addr + (((g)/10))) |= (((a)<=3?(a) + 4:(a)==4?3:2)<<(((g)%10)*3))
 
#define GPIO_SET  *(gpio.addr + 7)  // sets   bits which are 1 ignores bits which are 0
#define GPIO_CLR  *(gpio.addr + 10) // clears bits which are 1 ignores bits which are 0
 
#define GPIO_READ(g)  *(gpio.addr + 13) &= (1<<(g))

#define GPIO_PULL *(gpio.addr + 37) // pull up/pull down
#define GPIO_PULLCLK0 *(gpio.addr + 38) // pull up/pull down clock

 
// Exposes the physical address defined in the passed structure using mmap on /dev/mem
int map_peripheral(struct bcm2835_peripheral *p)
{
   if ((p->mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
      printf("Failed to open /dev/mem, try checking permissions.\n");
      return -1;
   }
   p->map = mmap(
      NULL, BLOCK_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED,
      p->mem_fd,      	// File descriptor to physical memory virtual file '/dev/mem'
      p->addr_p);       // Address in physical map that we want this memory block to expose
   if (p->map == MAP_FAILED) {
        perror("mmap");
        return -1;
   }
   p->addr = (volatile unsigned int *)p->map;
   return 0;
}
 
void unmap_peripheral(struct bcm2835_peripheral *p) 
{	munmap(p->map, BLOCK_SIZE);
	close(p->mem_fd);
}

 
// PART 2 - the multiplexing logic driving the front panel -------------

uint8_t ledrows[] = {20, 21, 22, 23, 24, 25, 26, 27};
uint8_t rows[] = {16, 17, 18};

#ifdef SERIALSETUP
uint8_t cols[] = {13, 12, 11,    10, 9, 8,    7, 6, 5,    4, 3, 2};  
#else
uint8_t cols[] = {13, 12, 11,    10, 9, 8,    7, 6, 5,    4, 15, 14};  
#endif


void *blink(int *terminate)
{
	int i,j,k,switchscan, tmp;

	// Find gpio address (different for Pi 2) ----------
	gpio.addr_p = bcm_host_get_peripheral_address() +  + 0x200000;
	if (gpio.addr_p== 0x20200000) printf("RPi Plus detected\n");
	else printf("RPi 2 detected\n");

	// set thread to real time priority -----------------
	struct sched_param sp;
	sp.sched_priority = 98; // maybe 99, 32, 31?
	if (pthread_setschedparam(pthread_self(), SCHED_FIFO, &sp))
	{ fprintf(stderr, "warning: failed to set RT priority\n"); }
	// --------------------------------------------------
	if(map_peripheral(&gpio) == -1) 
	{	printf("Failed to map the physical GPIO registers into the virtual memory space.\n");
		return (void *)-1;
	}

	// initialise GPIO (all pins used as inputs, with pull-ups enabled on cols)
	//	INSERT CODE HERE TO SET GPIO 14 AND 15 TO I/O INSTEAD OF ALT 0.
	//	AT THE MOMENT, USE "sudo ./gpio mode 14 in" and "sudo ./gpio mode 15 in". "sudo ./gpio readall" to verify.

	for (i=0;i<8;i++)					// Define ledrows as input
	{	INP_GPIO(ledrows[i]);
		GPIO_CLR = 1 << ledrows[i];		// so go to Low when switched to output
	}
	for (i=0;i<12;i++)					// Define cols as input
	{	INP_GPIO(cols[i]);
	}
	for (i=0;i<3;i++)					// Define rows as input
	{	INP_GPIO(rows[i]);
	}

	// BCM2835 ARM Peripherals PDF p 101 & elinux.org/RPi_Low-level_peripherals#Internal_Pull-Ups_.26_Pull-Downs
	GPIO_PULL = 2;	// pull-up
	short_wait();	// must wait 150 cycles
#ifdef SERIALSETUP
	GPIO_PULLCLK0 = 0x03ffc; // selects GPIO pins 2..13 (frees up serial port on 14 & 15)
#else
	GPIO_PULLCLK0 = 0x0fff0; // selects GPIO pins 4..15 (assumes we avoid pins 2 and 3!)
#endif
	short_wait();
	GPIO_PULL = 0; // reset GPPUD register
	short_wait();
	GPIO_PULLCLK0 = 0; // remove clock
	short_wait(); // probably unnecessary

	// BCM2835 ARM Peripherals PDF p 101 & elinux.org/RPi_Low-level_peripherals#Internal_Pull-Ups_.26_Pull-Downs
	GPIO_PULL = 0;	// no pull-up no pull-down just float
	short_wait();	// must wait 150 cycles
	GPIO_PULLCLK0 = 0x0ff00000; // selects GPIO pins 20..27
	short_wait();
	GPIO_PULL = 0; // reset GPPUD register
	short_wait();
	GPIO_PULLCLK0 = 0; // remove clock
	short_wait(); // probably unnecessary

	// BCM2835 ARM Peripherals PDF p 101 & elinux.org/RPi_Low-level_peripherals#Internal_Pull-Ups_.26_Pull-Downs
	GPIO_PULL = 0;	// no pull-up no pull down just float
// not the reason for flashes it seems:
//GPIO_PULL = 2;	// pull-up - letf in but does not the reason for flashes
	short_wait();	// must wait 150 cycles
	GPIO_PULLCLK0 = 0x070000; // selects GPIO pins 16..18
	short_wait();
	GPIO_PULL = 0; // reset GPPUD register
	short_wait();
	GPIO_PULLCLK0 = 0; // remove clock
	short_wait(); // probably unnecessary
	// --------------------------------------------------

	//printf("\nFP on\n");

	while(*terminate==0)
	{
		// prepare for lighting LEDs by setting col pins to output
		for (i=0;i<12;i++)
		{	INP_GPIO(cols[i]);			//
			OUT_GPIO(cols[i]);			// Define cols as output
		}
		
		// light up 8 rows of 12 LEDs each
		for (i=0;i<8;i++)
		{

			// Toggle columns for this ledrow (which LEDs should be on (CLR = on))
			for (k=0;k<12;k++)
			{	if ((ledstatus[i]&(1<<k))==0)
					GPIO_SET = 1 << cols[k];
				else 
					GPIO_CLR = 1 << cols[k];
			}	

			// Toggle this ledrow on
			INP_GPIO(ledrows[i]);	
			GPIO_SET = 1 << ledrows[i]; // test for flash problem
			OUT_GPIO(ledrows[i]);
//test			GPIO_SET = 1 << ledrows[i];



			nanosleep ((struct timespec[]){{0, intervl}}, NULL);
			
			// Toggle ledrow off
			GPIO_CLR = 1 << ledrows[i]; // superstition
			INP_GPIO(ledrows[i]);
usleep(10);  // waste of cpu cycles but may help against udn2981 ghosting, not flashes though
		}

//nanosleep ((struct timespec[]){{0, intervl}}, NULL); // test

		// prepare for reading switches		
		for (i=0;i<12;i++)
			INP_GPIO(cols[i]);			// flip columns to input. Need internal pull-ups enabled.
			
		// read three rows of switches
		for (i=0;i<3;i++)
		{
			INP_GPIO(rows[i]);//			GPIO_CLR = 1 << rows[i];	// and output 0V to overrule built-in pull-up from column input pin
			OUT_GPIO(rows[i]);			// turn on one switch row
			GPIO_CLR = 1 << rows[i];	// and output 0V to overrule built-in pull-up from column input pin

			nanosleep ((struct timespec[]){{0, intervl/100}}, NULL); // probably unnecessary long wait, maybe put above this loop also

			switchscan=0;
			for (j=0;j<12;j++)			// 12 switches in each row
			{	tmp = GPIO_READ(cols[j]);
			if (tmp!=0)
					switchscan += 1<<j;
			}
			INP_GPIO(rows[i]);			// stop sinking current from this row of switches

			switchstatus[i] = switchscan;
		}
	}

	//printf("\nFP off\n");
	// at this stage, all cols, rows, ledrows are set to input, so elegant way of closing down.

	return 0; 
}


void short_wait(void)					// creates pause required in between clocked GPIO settings changes
{
//	int i;
//	for (i=0; i<150; i++) {
//		asm volatile("nop");
//	}
	fflush(stdout); //
	usleep(1); // suggested as alternative for asm which c99 does not accept
}


unsigned bcm_host_get_peripheral_address(void)		// find Pi 2 or Pi's gpio base address
{
   unsigned address = get_dt_ranges("/proc/device-tree/soc/ranges", 4);
   return address == ~0 ? 0x20000000 : address;
}
static unsigned get_dt_ranges(const char *filename, unsigned offset)
{
   unsigned address = ~0;
   FILE *fp = fopen(filename, "rb");
   if (fp)
   {
      unsigned char buf[4];
      fseek(fp, offset, SEEK_SET);
      if (fread(buf, 1, sizeof buf, fp) == sizeof buf)
      address = buf[0] << 24 | buf[1] << 16 | buf[2] << 8 | buf[3] << 0;
      fclose(fp);
   }
   return address;
}