EDID as control channel - possible?

[showier-drastic]

Hi,

I would like to ask whether it is possible to turn the EDID I2C into a downstream control channel? Maybe via some magic usb command to modify EDID table?

[steve-m]

Yes, that is possible. So far there was no real use for this, so I didn't really clean up the code and commit it. Did that now in 9b910ef.

Here is some example code I used for testing.

Host side, can be plugged into hsdaoh_test.c:

int cnt = 1;
char message[256];

while (!do_exit) {
	sprintf(message, "Hello World via EDID #%d", cnt++);
	hsdaoh_write_edid_cmd_data(dev, (uint8_t *)message, strlen(message));
	usleep(100000);
}

Program running on a Raspberry Pi Pico connected via I2C to the MS2130:

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/i2c.h"

int main()
{
	stdio_init_all();

	i2c_init(i2c_default, 100 * 1000);
	gpio_set_function(PICO_DEFAULT_I2C_SDA_PIN, GPIO_FUNC_I2C);
	gpio_set_function(PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C);
	gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN);
	gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN);

	int ret;
	uint8_t txdata = 0;
	uint8_t rxdata;
	uint8_t msglen;
	uint8_t seq = 0x01;
	uint8_t last_seq = 0;

	while (true) {
		/* read sequence number */
		txdata = 0;
		ret = i2c_write_blocking(i2c_default, 0x50, &txdata, 1, false);
		if (ret < 0)
			continue;

		ret = i2c_read_blocking(i2c_default, 0x50, &rxdata, 1, false);
		if (ret < 0)
			continue;

		if ((rxdata != 0xff) && (rxdata != 0x00)) {
			seq = rxdata;
			if (seq != last_seq) {
				/* read length field */
				txdata = 1;
				ret = i2c_write_blocking(i2c_default, 0x50, &txdata, 1, false);

				if (ret < 0)
					continue;


				ret = i2c_read_blocking(i2c_default, 0x50, &msglen, 1, false);

				if (ret < 0)
					continue;

				txdata = 2;
				ret = i2c_write_blocking(i2c_default, 0x50, &txdata, 1, false);
				if (ret < 0)
					continue;

				/* read actual message */
				char message[256];
				ret = i2c_read_blocking(i2c_default, 0x50, message, msglen, false);
				if (ret < 0)
					continue;

				message[msglen] = '\0';
				printf("New message with length %d: %s\n", msglen, message);

				last_seq = seq;
			}
		}
	}

	return 0;
}