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Why i2c gio_read() not working?

William Liew
Prodigy 50 points

I got a problem with the following code:  After executing a routine sending a byte to a register of a slave device, then executing the following code, the result is rBuffer[1]=the old data sent onto the bus, not the data from the register with address 0x6. Please help.

    Int32                status = IOM_COMPLETED;
    I2c_DataParam        rxdataBuffer;

    rBuffer[0] = 0x6;
    rxdataBuffer.slaveAddr = I2C_SLAVE_ADDR;
    rxdataBuffer.buffer    = &rBuffer[0];
    rxdataBuffer.bufLen    =sizeof(rBuffer); 
    rxdataBuffer.flags     = I2c_READ | I2c_MASTER | I2c_START | I2c_STOP;

    status = GIO_read(i2c_inoutHandle, &rxdataBuffer,
                        &rxdataBuffer.bufLen); 

 

  • 0
    Guru 26430 points

    I'm not sure what are your test conditions. Did you write the address and read the data as separate I2C transactions? The code fragment almost suggests you are trying to a write and read in one I2C GIO request. You'll need a repeated start for that. How does your slave device expect the register address to be sent and data to be read?

     

  • 0 in reply to Norman Wong
    Prodigy 50 points

    I am trying to read from the slave address in the master C6748 I2C. Could you please modify the code to make it work?

  • 0 in reply to William Liew
    Guru 26430 points

    Not enough detail to go on. You should take a look at the I2C examples in the PSP package. They are at

    pspdrivers_01_30_01\packages\ti\pspiom\examples\evm6748\i2c
    pspdrivers_01_30_01\packages\ti\pspiom\examples\evmOMAPL138\i2c

    The examples appear to be write only. You should use them to check that data is actually coming out the I2C port. Check with with a scope.

     

  • 0 in reply to Norman Wong
    Prodigy 50 points

    Those TI examples do not cover GIO_read into the DSP I2C, even though it works perfectly for GIO_write out of the DSP to the I2C LED blinking on the EVM board. I have spent a lot of time on those examples and they certainly work, but they do not cover GIO_read for the I2C. If you did not work on those examples, please ask your colleagues and hope they could help me. Thanks anyway.

  • 0 in reply to William Liew
    Guru 26430 points

    I am guessing your slave requires a repeated start transaction. I've used the GIO for SPI. Haven't tried it for I2C. The I2C code for reading a 8 bit register should look something like:

    Int32 readreg(Uint8 devaddr, Uint8 regaddr, Uint8 *data)
    {
      Int32         status = IOM_COMPLETED;
      I2c_DataParam param;

      param.slaveAddr = devaddr;
      param.buffer    = &regaddr;
      param.bufLen    = 1;
      param.flags     = I2c_WRITE | I2c_MASTER | I2c_START;

      status = GIO_write(i2c_inoutHandle, &param, sizeof(param));
      if(status!=IOM_COMPLETED) return(status);

      param.slaveAddr = devaddr;
      param.buffer    = data;
      param.bufLen    = 1;
      param.flags     = I2c_READ | I2c_MASTER | I2c_START | I2c_STOP;

      status = GIO_read(i2c_inoutHandle, &param, sizeof(param));
      return(status);
    }

    Good luck.