P9.15 is not working with BeagleBoneBlack REV.C3 and Debian 7.11

General Discussion
1

When I tried to run software that reads GPIO (P9.15) with BeagleBoneBlack REV.C3 under Debian 7.11, it always reads “0”.
On the other hand, BeagleBoneBlack REV.C2 + Debian7.11 works fine.

The official PCN for rev. C3 states “CUSTOMER ACTION REQUIRED: No actions.”

If anyone has any information on this issue, please give me some information.

The test code I am using is as follows.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <poll.h>
#include <string.h>

#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>

typedef enum GPIO_DIRECTION_t {
    IN,
    OUT
} GPIO_DIRECTION_t;

typedef enum GPIO_ACTIVE_TRIGGER_t {
    RISING,
    FALLING,
    BOTH
} GPIO_ACTIVE_TRIGGER_t;

typedef struct GPIO_t {
    int num;
    GPIO_DIRECTION_t dir;
    GPIO_ACTIVE_TRIGGER_t trigger;
    int value_fd;
} GPIO_t;

int gpio_open(GPIO_t * gpio, int num, GPIO_DIRECTION_t dir)
{
    int fd;
    FILE *fp;
    char file_path[100];

    fp = fopen("/sys/class/gpio/export", "w");
    if(fp == NULL) {
        return -1;
    }

    fprintf(fp, "%d", num);
    gpio->num = num;
    fclose(fp);

    sprintf(file_path, "/sys/class/gpio/gpio%d/direction", num);
    fp = fopen(file_path, "w");
    if(fp == NULL) {
        return -2;
    }

    if(dir == IN) {
        fprintf(fp, "%s", "in");
    }
    else {
        fprintf(fp, "%s", "out");
    }

    gpio->dir = dir;
    fclose(fp);

    sprintf(file_path, "/sys/class/gpio/gpio%d/value", num);
    fd = open(file_path, O_RDWR | O_SYNC);
    if(fd < 0) {
        return -3;
    }

    gpio->value_fd = fd;

    return 0;
}

int gpio_close(GPIO_t * gpio)
{
    FILE *fp;

    close(gpio->value_fd);

    fp = fopen("/sys/class/gpio/unexport", "w");
    if(fp == NULL) {
        return -1;
    }

    fprintf(fp, "%d", gpio->num);
    fclose(fp);

    return 0;
}

int gpio_out_value(GPIO_t * gpio, int value)
{
    if(gpio->dir != OUT) {
        return -1;
    }

    if(value == 0) {
        write(gpio->value_fd, "0", 1);
    }
    else {
        write(gpio->value_fd, "1", 1);
    }

    lseek(gpio->value_fd, 0, SEEK_SET);

    return 0;
}

int gpio_in_value(GPIO_t * gpio, int * value)
{
    char buff[100];

    if(gpio->dir != IN) {
        return -1;
    }

    read(gpio->value_fd, buff, 100);
    lseek(gpio->value_fd, 0, SEEK_SET);

    *value = atoi(buff);
    return 0;
}

/****************************************************************
* Main
****************************************************************/
int main(void)
{
    int result;
    int value;

    GPIO_t  MYPORT;

    result = gpio_open(&MYPORT, 48, IN);
    printf("GPIO P9_15 open : %d\n", result);

    gpio_in_value(&MYPORT, &value); // <-- *always read "0" in REV.C3*
    printf("P9.15 = %d\n", value);
}
1 Like
2

Should not be any difference. It would be interesting to compare boot logs, to see if they are detected and booting exactly the same…

Regards,

1 Like
3

Thank you RobertCNelson for your comments.

As you say, I have also looked through the schematics and other documentation, and I can’t find any software differences between REV.C2 and REV.C3.

In the meantime, I will check and compare the boot logs and report back.

4

When I checked again, it was not the difference between REV.C2 and REV.C3.

When booting with Debian 7.11 on MicroSD, the above program does not seem to work (0 is always read from P9.15) if Debian 7.11 is burned on EMMC. On the other hand, if Debian 10.3 is burned on EMMC, it works fine.

If anyone has any ideas about this situation, please let me know.