Slow i2cdetect command response after running a program using the pigpio library

Question

System: RPi # B OS: Ubuntu-16.04 Ma'te desktop environment Problem: i2cdetect -y 1 command response ultra-slow after running a program using the pigpio library in a program.

Since I've had no luck with the wiringPi library with talking to a MCP23017 IO expander I thought I'd try the pigpio library.

Well reading and writing the MCP23017 registers works. gpioInitialise(), i2cOpen(), i2cClose(), & gpioTerminate() functions along with register read/writes work properly.

If a read/write fails I'd use the i2cdetect tool to verify the MCP23017 id seated OK in the breadboard. It has a habit of unseating itself on the pins 1 ... 14 side.

When I execute the i2cdetect command after reseating the MC_23017 the command response is super slow. I also get a ton of messages in syslog transfer timeouts:

Jun 22 19:39:06 rpi3b2 kernel: [18443.461850] i2c i2c-1: transfer timed out
Jun 22 19:39:07 rpi3b2 kernel: [18444.461859] i2c i2c-1: transfer timed out
Jun 22 19:39:08 rpi3b2 kernel: [18445.461901] i2c i2c-1: transfer timed out
Jun 22 19:39:09 rpi3b2 kernel: [18446.461903] i2c i2c-1: transfer timed out
Jun 22 19:39:10 rpi3b2 kernel: [18447.461916] i2c i2c-1: transfer timed out
Jun 22 19:39:11 rpi3b2 kernel: [18448.461929] i2c i2c-1: transfer timed out
Jun 22 19:39:12 rpi3b2 kernel: [18449.461918] i2c i2c-1: transfer timed out
Jun 22 19:39:13 rpi3b2 kernel: [18450.461928] i2c i2c-1: transfer timed out
Jun 22 19:39:14 rpi3b2 kernel: [18451.461929] i2c i2c-1: transfer timed out
Jun 22 19:39:15 rpi3b2 kernel: [18452.461946] i2c i2c-1: transfer timed out
Jun 22 19:39:16 rpi3b2 kernel: [18453.461929] i2c i2c-1: transfer timed out
Jun 22 19:39:17 rpi3b2 kernel: [18454.461957] i2c i2c-1: transfer timed out
Jun 22 19:39:18 rpi3b2 kernel: [18455.461944] i2c i2c-1: transfer timed out
Jun 22 19:39:19 rpi3b2 kernel: [18456.461917] i2c i2c-1: transfer timed out

I have to reboot the Pi to get a normal i2cdetect command response. However if I run the pigpio program the same result occur.

Can anyone help/provide an explaination on this? Much appriciated.

    /*-------------------------------------------------------------------------------
 * pgbl_01.c
 * pigpio library.
 * Blink LEDs program #1.
 */

/*-------------------------------------------------------------------------------
 * Includes.
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <pigpio.h>

/*-------------------------------------------------------------------------------
 * Global constants & variables.
 */

#define NUM_PINS 5
unsigned pins[] = { 5, 6, 13, 19, 26 };

/*-------------------------------------------------------------------------------
 * Helper functions.
 */

// Print an 8-bit register value in binary.
// 
const char* printb8(int x) {
    static char b[9];
    b[0] = '\0';
    int z;
    for (z = 128; z > 0; z >>= 1) {
        strcat(b, ((x & z) == z) ? "1" : "0");
    }
    return b;
} /* End printb */

// Press Any Key To Continue.
//
void paktc(){
    printf("Press any key to continue...\n");
    getchar();
    //printf("%c\n", ch);
} /* End paktc */

/*-------------------------------------------------------------------------------
  * Main function.
  */

int main(int argc, char **argv) {
    char *message = "HELLO WOILD from the C programming language!!\n\n";
    printf("%s", message);

    if (gpioInitialise() < 0) {
        fprintf(stderr, "pigpio initialisation failed.\n");
        return(1);
    }
    else {
        printf("pigpio initialisation OK.\n");
    }

    // Set pins for output low, delay 1 min, then high.
    //
    for (int p = 0; p < NUM_PINS; p++) {
        gpioSetMode(p, PI_OUTPUT);
        gpioWrite(pins[p], 0x00);
        sleep(1);
        gpioWrite(pins[p], 0x01);
    }

    // Clean up and close pigpio.
    //
    gpioTerminate();
    printf("Done.\n");
} /* End main() */

Answer 1

In the pigpio code there is an error in your gpioSetMode() call.

You are setting GPIO 0-4 to be outputs. GPIO 0-3 are the I2C buses GPIO. That will totally confuse the I2C system as it expects them to be in mode ALT0.

Replace

gpioSetMode(p, PI_OUTPUT);

with

gpioSetMode(pins[p], PI_OUTPUT);