Re: I2C again

[Jeff Sutherland <jeffs@xxxxxxxxxxxxxxxxxx>]

On Saturday 29 November 2008, viper@xxxxxxxxxxx wrote:> Hi all,>> I’m trying to use a Texas Instruments TMP175 temprature sensor on an> AT91RM9200 system ( i2c-gpio).>> The code (part of it):>> //global vars> int i2c_handler;>> int main( int argc, char *argv[] ) {>     int i=0;>     int value=0;>     int adapter_nr;>     int err;>     int funcs;>     char buf[8];>>     //we don't have to initialize the I2C, since it's done by the driver>>     //opening the device>     printf("Opening /dev/i2c\n");>     if ( ( err = ( i2c_handler = open("/dev/i2c-0",O_RDWR) ) ) < 0 ) {>         printf("Error opening /dev/i2c-0! Exiting (%d -> %s).\n",err,strerror(errno));>         exit(1);>     }>>     // check for req funcs>     printf("Getting available IOCTLs\n");>     // get funcs list>     if((err = ioctl(i2c_handler, I2C_FUNCS, &funcs) < 0)) {>         printf( "Error eeprom_open: %s\n", strerror(err));>         exit(1);>     }>     CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_BYTE );>     CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_BYTE );>     CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_BYTE_DATA );>     CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_BYTE_DATA );>     CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_WORD_DATA );>     CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_WORD_DATA );>>     printf("Setting slave addr to 0x79\n");>     if ( ( err = ioctl(i2c_handler,I2C_SLAVE,0x79) ) < 0 ) {>         printf("Error setting SLAVE address! Exiting (%d).\n",err);>         exit(1);>     }>>     value = i2c_smbus_read_byte(i2c_handler);>     if ( value < 0 )>         fprintf( stderr, "Failed to read from I2C device: %m\n" );>>     printf("Reading with read\n");>     if ( read(i2c_handler,buf,1) != 1 ) {>         printf("Error reading byte! (%s)\n",buf);>     }>>     printf("Reading with i2c_read\n");>     if ( ( value = i2c_smbus_read_byte(i2c_handler)) < 0 ) {>         printf("Error readiny byte! (%d)\n",value);>     }>>     printf("Trying direct write!\n");>     buf[0] = 0;>>     if ( write(i2c_handler,buf,1) != 1 ) {>         printf("Error writing byte! (%s)\n",buf);>         return -1;>     }>> The result:> root@(none):/mnt/tmp175# ./tmp175> Opening /dev/i2c> Getting available IOCTLs> Setting slave addr to 0x79> Failed to read from I2C device: Operation not permitted> Reading with read> Error reading byte! (X†)> Reading with i2c_read> Error readiny byte! (-1)> Trying direct write!> Error writing byte! ()>> The ’dmesg’ output, since debug messages are turned on:> i2c-adapter i2c-0: ioctl, cmd=0x705, arg=0xbee5fde4> i2c-adapter i2c-0: ioctl, cmd=0x703, arg=0x79> i2c-adapter i2c-0: ioctl, cmd=0x720, arg=0xbee5fd74> i2c-adapter i2c-0: master_xfer[0] R, addr=0x79, len=1> i2c-adapter i2c-0: NAK from device addr 0x79 msg #0> i2c-dev: i2c-0 reading 1 bytes.> i2c-adapter i2c-0: master_xfer[0] R, addr=0x79, len=1> i2c-adapter i2c-0: NAK from device addr 0x79 msg #0> i2c-adapter i2c-0: ioctl, cmd=0x720, arg=0xbee5fd74> i2c-adapter i2c-0: master_xfer[0] R, addr=0x79, len=1> i2c-adapter i2c-0: NAK from device addr 0x79 msg #0> i2c-dev: i2c-0 writing 1 bytes.> i2c-adapter i2c-0: master_xfer[0] W, addr=0x79, len=1> i2c-adapter i2c-0: NAK from device addr 0x79 msg #0>> What’s wrong? Am I just lame, or it’s something with the device?>> Thanks,>>                 Tamas
I suspect your slave address is wrong.  For example, if the docs say your device's slave address is 0x26, you need to use a value of 0x13  (shift 1 >> or divide by 2) in the ioctl operations.
-Jeff-- Secure your email with Gnu Privacy Guard and Thunderbird, the open sourcecross platform solution for Windows, Linux, and Mac OS X.See http://enigmail.mozdev.org/
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