I2C random read of off-board device from within PRU not working correctly

[Hugh Frater]

Does anyone know the correct programming sequence for doing an I2C random read from within the PRU? I've tried this nicely written driver:

https://github.com/LinuxDroneLab/pru-i2c-lib

It works less than my code does...

My code works fine if I call my routine once, on the scope I see the write followed by the read of the 2 bytes I want... Call my function again and all I see is the read.

Code and scope grabs attached - the documentation on the I2C module from within the AM335xTRM pdf is shocking and this problem is driving me mad... 

/*

 * read_wiper - returns the 2nd byte of a 2-byte read from the specified wiper

 * 'reg' contains the write command to read the required wiper

 */

uint8_t read_wiper(uint8_t reg)

{

    uint8_t dataByte;

    //initialise i2c2 device

    init_i2c();

    //set I2C2_CNT register to 1 for initial write command

    I2C2_CNT = 1;

    while (!(I2C2_STATUSRAW & 0x0100));

        //poll 'buss free' bit in I2C2_STATUSRAW register (bit 8) until it is non-zero

    //set transmit mode

    I2C2_CON = 0x8601;

    //load data register with write command

    I2C2_DATA = reg;

    while (!(I2C2_STATUSRAW & 0x0004));

        //poll 'access ready' bit in I2C2_STATUSRAW register (bit 4) until it is non-zero

    //set byte count to 2

    I2C2_CNT = 2;

    //set receive mode

    I2C2_CON = 0x8403;

    while (!(I2C2_STATUSRAW & 0x0008));

        //poll 'receive ready bit' in I2C2_STATUSRAW register (bit 3) until it is non-zero

    dataByte = I2C2_DATA;   //first byte is always 0x00

    //zero the receive ready bit once we have read the 1st byte into our local variable

    I2C2_STATUSRAW |= 0x0008;

    while (!(I2C2_STATUSRAW & 0x0008));

        //poll 'receive ready bit' in I2C2_STATUSRAW register (bit 3) until it is non-zero

    dataByte = I2C2_DATA;   //second byte is the value we want

    //zero the receive ready bit once we have read the 2nd byte into our local variable

    I2C2_STATUSRAW |= 0x0008;

    while (!(I2C2_STATUSRAW & 0x0100));

        //poll 'buss free' bit in I2C2_STATUSRAW register (bit 8) until it is non-zero

    return dataByte;

}

void init_i2c()

{

    /* Enable I2C2 clock signal generation */

    while (!(CM_PER_I2C2 & 0x2))

        CM_PER_I2C2 |= 0x2;

    /*

     *  set I2C2_PSC register to 0x0B

     *  set I2C2_SCCL register to 0x0D

     *  set I2C2_SCCH register to 0x0F

     *  set I2C2_CON register to 1000 0110 0000 0000 (0x8600)

     *  set I2C2_SA register to 0x2E (address of MCP4641)

     */

    I2C2_PSC = 0x000B;

    I2C2_SCLL = 0x000D;

    I2C2_SCLH = 0x000F;

    I2C2_CON = 0x8600;

    I2C2_SA = i2cPotAddress;

    I2C2_BUF = 0x0000;

}

[Mark Lazarewicz]

I love the TRM documentation its very detailed best to follow its recommended sequences and roll your own code using examples as a template. 

I'd look at the i2C slave data sheet carefully especially the timing/setup diagrams.

 you have the scope looks like your close.Another idea look for example code for device even if another micro. Looking at it might give you a clue what's wrong. Last attempt try something quick and simple if you have available no OS barebones one processor I bet your code works on it.

Good Luck

Sent from Yahoo Mail on Android

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[Hugh Frater]

Got this working with a few code changes:

/*

 * read_wiper - returns the 2nd byte of a 2-byte read from the specified wiper

 * 'reg' contains the write command to read the required wiper

 */

uint8_t read_wiper(uint8_t reg)

{

    uint8_t dataByte;

    //initialise i2c2 device

    init_i2c();

    //set I2C2_CNT register to 1 for initial write command

    I2C2_CNT = 1;

    while (I2C2_STATUSRAW & 0x1000);

        //poll 'busy bit' in I2C2_STATUSRAW register (bit 12) until it is zero

    //set transmit mode

    I2C2_CON = 0x8601;

    //load data register with write command

    I2C2_DATA = reg;

    while (!(I2C2_STATUSRAW & 0x0010));

        //poll XRDY bit in I2C2_STATUSRAW register (bit 4) until it is non-zero

    //data has transmitted, write 1 to clear the interrupt

    I2C2_STATUSRAW |= 0x0010;

    while (!(I2C2_STATUSRAW & 0x0004));

        //poll 'access ready' bit in I2C2_STATUSRAW register (bit 4) until it is non-zero

    //set byte count to 2

    I2C2_CNT = 2;

    //set receive mode

    I2C2_CON = 0x8400;

    //set start and auto stop condition

    I2C2_CON |= 0x0003;

    while (!(I2C2_STATUSRAW & 0x0008));

        //poll 'receive ready bit' in I2C2_STATUSRAW register (bit 3) until it is non-zero

    dataByte = I2C2_DATA;   //first byte is always 0x00

    //data has been received, write 1 to clear the interrupt

    I2C2_STATUSRAW |= 0x0008;

    while (!(I2C2_STATUSRAW & 0x0008));

        //poll 'receive ready bit' in I2C2_STATUSRAW register (bit 3) until it is non-zero

    dataByte = I2C2_DATA;   //second byte is the value we want

    //data has been received, write 1 to clear the interrupt

    I2C2_STATUSRAW |= 0x0008;

    while (!(I2C2_STATUSRAW & 0x0100));

        //poll 'buss free' bit in I2C2_STATUSRAW register (bit 8) until it is non-zero

    //clear all pending interrupts

    I2C2_STATUS = 0x7FF;

    return dataByte;

}

Note the clearing of pending interrupts after each check and the final clear of the status register (not status_raw) at the end. 5 byte writes now working every time...