Pioneer SR-link control - Raspberry PI

srlink.c

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <errno.h>
#include <stdint.h>

// SR Control pulses (IR pulses without modulation)
#define HDR_MARK    9000
#define HDR_PAUSE   4500
#define BIT_MARK    560
#define ONE_PAUSE   1600
#define ZERO_PAUSE  560

// SR Control codes:
#define SR_VOLUME_UP    0xA55A50AF
#define SR_VOLUME_DOWN  0xA55AD02F
#define SR_TOGGLE_PWR   0xA55A38C7
#define SR_INPUT_HDMI   0xA55A7A85

static volatile uint32_t *gpio;

void sendCode(unsigned long data, int nbits);
void sendPulse(long microsecs);

int main(int argc, char **argv)
{
	int fd, i;

	// Open memory handle
	if ((fd = open ("/dev/mem", O_RDWR | O_SYNC) ) < 0) {
		printf("Unable to open /dev/mem: %s\n", strerror(errno));
		return -1;
	}

	// map memory to gpio at offset 0x20200000 (gpio start..)
	gpio = (uint32_t *)mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0x20200000);

	if ((int32_t)gpio < 0){
		printf("Mmap failed: %s\n", strerror(errno));
		return -1;
	}

	//set gpio17 as an output
	*(gpio + 1) = (*(gpio + 1) & ~(7 << 21)) | (1 << 21);

	//set gpio17 high:
	*(gpio + 7) = 1 << 17;
	sleep(1);

	for (i = 0; i < 5; i++) {
		sendCode(SR_VOLUME_UP, 32);
		sleep(1);
		sendCode(SR_VOLUME_DOWN, 32);
		sleep(1);
	}
}

void sendPulse(long microsecs)
{
	// Take GPIO 17 low, wait, then high. (one pulse..)
	*(gpio + 10) = 1 << 17;
	usleep(microsecs);
	*(gpio + 7) = 1 << 17;
}

void sendCode(unsigned long data, int nbits)
{
	int i;
	
	sendPulse(HDR_MARK);
	usleep(HDR_PAUSE);
	
	for (i = 0; i < nbits; i++)
	{
		sendPulse(BIT_MARK);
		
		if (data & 0x80000000)
			usleep(ONE_PAUSE);
		else
			usleep(ZERO_PAUSE);
		
		data <<= 1;
	}
}

SR link appears to have a common header: A5 5A
then a one byte command and a one byte checksum. Command and checksum add to hex FF (255)
I wonder if those commands are publshed by Pioneer?

SR is a common bus, and so every command is broadcast to every device daisy-chained together. A5 is the device type identifier for receivers. (A1 is tape decks, A2 is CD players, etc.) The format of a simple SR command is [frame header][device type ID][bitwise negation of device type ID][command code][bitwise negation of command code][stop bit].

So, yes, all commands intended for your receiver will start with A55A (5A being the happy-accident bitwise negation of A5). But all commands intended for your CD player will start with A25D (5D being the bitwise negation of A2).

And yes, many of the command codes were published by Pioneer. But they’re also just the exact same command codes sent by the device’s infrared remote, which have been extensively cataloged.