对从RPI到HMCL3855L的I2C通信进行故障排除

Question

I'm trying to figure out how to communicate with the HMC3855L compass module using a Raspberry Pi running Arch linux.

Currently I've got the connections all set up and I can see the device address (0x1E) using the unix tool i2cdetect but when every I try and run my code I get nothing. I'm using the Bcm2835 library by Mike McCauley for the C programming.

I'm fairly new to programming in C but so I just need something quick and dirty to read some bytes off this thing. I checked and made sure all my arrays contained the correct values and that the pointers were pointing to the appropriate addresses. Everytime I run my script and check i2cdetect again the address changes from (0x1E) to (0x03) which is pretty strange. Any advice on the matter would be greatly appreciated. Code is as follows...

/* i2ccompass:
* Test script for continuously reading data from i2c compass
* device and logging to a file.
*
*/

#include <bcm2835.h>
#include <stdio.h>

uint16_t clk_div = BCM2835_I2C_CLOCK_DIVIDER_148;
uint8_t slave_address = 0x1E;
uint64_t delay = 70000;

int main(void) {

    if (!bcm2835_init()) return 1;
    bcm2835_i2c_begin();
    bcm2835_i2c_setSlaveAddress(slave_address);

    printf("Clock divider set to: %d\n", clk_div);
    printf("Slave address set to: %d or %X\n",slave_address,slave_address);

    char writeBuff[3] = {0x3C,0x00,0x70};
    char gainBuff[3] = {0x3C,0x01,0xA0};
    char modeBuff[3] = {0x3C,0x02,0x00};
    char startTransBuff[2] = {0x3D,0x06};
    char repeat[2] = {0x3C,0x03};
    char readBuff[10];

    char *wb_ptr, *gb_ptr, *mb_ptr,
          *stb_ptr, *r_ptr, *re_ptr;
    wb_ptr = writeBuff;
    gb_ptr = gainBuff;
    mb_ptr = modeBuff;
    stb_ptr = startTransBuff;
    r_ptr = readBuff;
    re_ptr = repeat;

    bcm2835_i2c_write(wb_ptr, 3);
    bcm2835_delayMicroseconds(delay);
    bcm2835_i2c_write(gb_ptr, 3);
    bcm2835_delayMicroseconds(delay);
    bcm2835_i2c_write(mb_ptr, 3);
    bcm2835_delayMicroseconds(delay);
    bcm2835_i2c_write(stb_ptr, 2);

    bcm2835_delayMicroseconds(delay);

    bcm2835_i2c_read(r_ptr, 6);
    int i = 1;
    for(i; i <= 10; i++){
     printf("Read Buf[%d] = %x or %d\n",
          i-1, readBuff[i-1], readBuff[i-1]);
    }
    bcm2835_delayMicroseconds(delay);

    bcm2835_i2c_write(re_ptr, 2);

    bcm2835_i2c_end();
    bcm2835_close();
    printf("... done\n");
        return 0;
}

Answer 1

I dont see anything unusual in the code you hava provided but suspect function bcm2835_i2c_write().

The amount of delay could also cause the problem. You have not provided any delay after setting slave address migh cause a problem.

Answer 2

The steps on debugging any I2C device

1.Verify your hardware connection is ok (especially SCL and SDA)

2.Verify that does your API uses the slave address correctly as expected by the i2c slave ie;HMC3855L and after sending slave address verify you're receiving ACK signal as response.

3.Verify you're configuring the control registers correectly . In some i2c devices initially when it starts they might be in power down mode so we have to change it by setting some bits in the control register

4.Mainly the timing diagram for read & write is the most important and more prone to have mistakes, ie; note where are the start and stop conditions are used (most of them use repeated start), If you're just writing a API driver code you must have to understand how the i2c read & write works inside the kernel

5.Conversion of data might take some time , so check that information in datasheet electrical characteristics section

Considering all these informations I hope you'll be able to solve problem