Unexpected staus with I2C on Raspberry Pi

Question

I am writing c++ code (but my example is straight c) to talk to an AdaFruit Servo Motor Pi Hat, which uses the I2C bus to communicate with the Pi. I'm having a problem when trying to use the ioctl I2C_RDWR mechanism. I am getting a 'Bad Address' status back from the call. It doesn't matter what address I give it (the hat answers to 0x40, though), it always fails. I've boiled the code down into a short module, which is self contained. This is my first post to this site, so if I've done any faux pas, please forgive me.

When I run the attached code, I get the following response:

I2C_FUNC_I2C                            OK
I2C_FUNC_10BIT_ADDR 
I2C_FUNC_PROTOCOL_MANGLING 
I2C_FUNC_SMBUS_QUICK                    OK
I2C_FUNC_SMBUS_READ_BYTE                OK
I2C_FUNC_SMBUS_WRITE_BYTE               OK
I2C_FUNC_SMBUS_READ_BYTE_DATA           OK
I2C_FUNC_SMBUS_WRITE_BYTE_DATA          OK
I2C_FUNC_SMBUS_READ_WORD_DATA           OK
I2C_FUNC_SMBUS_WRITE_WORD_DATA          OK
I2C_FUNC_SMBUS_PROC_CALL                OK
I2C_FUNC_SMBUS_READ_BLOCK_DATA 
I2C_FUNC_SMBUS_WRITE_BLOCK_DATA         OK
I2C_FUNC_SMBUS_READ_I2C_BLOCK           OK
I2C_FUNC_SMBUS_WRITE_I2C_BLOCK          OK
Write failed: Bad address

My Pi is a model B, version 2. I have enabled the i2c system and can see the i2c device:

crw-rw-rw- 1 root i2c    89,   1 Aug 31 23:02 i2c-1

Any help would be appreciated.

The code follows:

#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/i2c-dev.h>
#include <linux/i2c.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>


int main() {
    int file;
    int devAddr = 0x40;
    int status;
    uint32_t funcs;
    uint8_t data = 0xAA;
    struct i2c_rdwr_ioctl_data request;
    struct i2c_msg ioctlMsg[1];

    file = open("/dev/i2c-1", O_RDWR);
    if(file < 0) {
            perror("could not open device");
            return 1;
    }
    status = ioctl(file, I2C_FUNCS, &funcs);
    if(status < 0) {
            perror("could not get funcs");
            return 3;
    }
    fprintf(stderr, "\nI2C_FUNC_I2C ");
    if ( I2C_FUNC_I2C & funcs) fprintf(stderr, "\t\t\t\tOK");      
    fprintf(stderr, "\nI2C_FUNC_10BIT_ADDR ");
    if ( I2C_FUNC_10BIT_ADDR & funcs)  fprintf(stderr, "\t\t\tOK");
    fprintf(stderr, "\nI2C_FUNC_PROTOCOL_MANGLING ");                 
    if ( I2C_FUNC_PROTOCOL_MANGLING & funcs) fprintf(stderr, "\tOK");       
    fprintf(stderr, "\nI2C_FUNC_SMBUS_QUICK ");
    if ( I2C_FUNC_SMBUS_QUICK & funcs) fprintf(stderr, "\t\t\tOK");
    fprintf(stderr, "\nI2C_FUNC_SMBUS_READ_BYTE ");
    if ( I2C_FUNC_SMBUS_READ_BYTE & funcs) fprintf(stderr, "\t\tOK");
    fprintf(stderr, "\nI2C_FUNC_SMBUS_WRITE_BYTE ");
    if ( I2C_FUNC_SMBUS_WRITE_BYTE & funcs) fprintf(stderr, "\t\tOK");
    fprintf(stderr, "\nI2C_FUNC_SMBUS_READ_BYTE_DATA ");
    if ( I2C_FUNC_SMBUS_READ_BYTE_DATA & funcs) fprintf(stderr, "\t\tOK");
    fprintf(stderr, "\nI2C_FUNC_SMBUS_WRITE_BYTE_DATA ");
    if ( I2C_FUNC_SMBUS_WRITE_BYTE_DATA & funcs) fprintf(stderr, "\t\tOK");
    fprintf(stderr, "\nI2C_FUNC_SMBUS_READ_WORD_DATA ");
    if ( I2C_FUNC_SMBUS_READ_WORD_DATA & funcs) fprintf(stderr, "\t\tOK");
    fprintf(stderr, "\nI2C_FUNC_SMBUS_WRITE_WORD_DATA ");
    if ( I2C_FUNC_SMBUS_WRITE_WORD_DATA & funcs) fprintf(stderr, "\t\tOK");
    fprintf(stderr, "\nI2C_FUNC_SMBUS_PROC_CALL ");  
    if ( I2C_FUNC_SMBUS_PROC_CALL & funcs) fprintf(stderr, "\t\tOK"); 
    fprintf(stderr, "\nI2C_FUNC_SMBUS_READ_BLOCK_DATA ");  
    if ( I2C_FUNC_SMBUS_READ_BLOCK_DATA & funcs) fprintf(stderr, "\t\tOK"); 
    fprintf(stderr, "\nI2C_FUNC_SMBUS_WRITE_BLOCK_DATA ");  
    if ( I2C_FUNC_SMBUS_WRITE_BLOCK_DATA & funcs) fprintf(stderr, "\tOK"); 
    fprintf(stderr, "\nI2C_FUNC_SMBUS_READ_I2C_BLOCK ");  
    if ( I2C_FUNC_SMBUS_READ_I2C_BLOCK & funcs) fprintf(stderr, "\t\tOK"); 
    fprintf(stderr, "\nI2C_FUNC_SMBUS_WRITE_I2C_BLOCK ");  
    if ( I2C_FUNC_SMBUS_WRITE_I2C_BLOCK & funcs) fprintf(stderr, "\t\tOK"); 
    fprintf(stderr, "\n");


    memset(ioctlMsg, 0, sizeof(struct i2c_rdwr_ioctl_data) * 2);
    ioctlMsg[0].addr = 0x0;
    ioctlMsg[0].flags = 0;          /* write command */
    ioctlMsg[0].len = 1;
    ioctlMsg[0].buf = &data;
    request.msgs = ioctlMsg;
    request.nmsgs = 1;
    status = ioctl(file, I2C_RDWR, request);
    if(status < 0) {
            perror("Write failed");
            return 2;
    }
    close(file);
    return 0;
}

Jim Noeth Jim Noeth · Accepted Answer · 2016-09-01T13:15:07

I found my problem, turns out that the 'bad address' wasn't referring to the address of the I2C device, but the address of the block being sent in the ioctl command. I had forgotten to pass the address, as opposed to the value of the parameter in my call to ioctl.

Unexpected staus with I2C on Raspberry Pi

1 Answers