TPS92682-Q1: parity bit calculation for SPI communication question

Hi Tuan!

It seems that SPI protocol have been set correctly, and the issue is in incorrect parity bit calculation.

Today I moved forward a little bit, and now I have at least correct algorithm to calculate parity bit for write commands. But, surprisingly, it does not work for read commands! See there:  The last variant is for read operation, and parity bit has to be 0.

Why does this happens?

I have double checked SPI connection with logic analyzer, and everything seems to be ok.

My question is: how to calculate parity bit in correct way? If you have software example - it will be nice. I have an ability to check it, and if there are some issues on my side, it will not work.

I made an example to check all values which may be written to a register, and here is results.

You may see implementation of data transmission functions below in "code"section.

/*!****************************************************************************
* @brief    Write data to register
*/
eDrvError writeReg(uint8_t addr, uint8_t data){
    eDrvError exitStatus = drvUnknownError, drvExStatus;
    uint8_t rxData[TRANSACTION_BYTES], txData[TRANSACTION_BYTES];
    
    //Compose command bit, address and parity bit
    txData[0] = composeCmdByte(CMD_BIT_WRITE, addr, data);
    txData[1] = data;
    //Perform transaction with received packet checking
    hw_wrap_spiTxRx(txData, rxData, TRANSACTION_BYTES);
    drvExStatus = hw_wrap_spiTxRx(txData, rxData, TRANSACTION_BYTES);
    if(drvExStatus == drvNoError){
        txData[0] = txData[0] >> PARITY_BIT_POS;
        if(((rxData[0] & ((~SPI_ERROR_BIT) & BYTE_MASK)) == txData[0]) && (rxData[1] == txData[1]) && ((rxData[0] & SPI_ERROR_BIT) == 0)){
            exitStatus = drvNoError;
        }else if((rxData[0] & SPI_ERROR_BIT) != 0){
            //TO DO: implement errors proccessing
            exitStatus = drvHwError;
        }
    }
    
    return exitStatus;
}

/*!****************************************************************************
* @brief    Compose command byte of cmd bit, address and parity bit
* @param    Commmand bit
* @param    6-bit address
* @param    Data-to-transmit byte
*/
uint8_t composeCmdByte(uint8_t cmd, uint8_t addr, uint8_t data){
    uint8_t cmdByte, parity;
    
    //Compose command byte
    cmdByte = ((addr & ADDRESS_MSK) << PARITY_BIT_POS) | (cmd << CMD_BIT_POS);
    //Calculate parity bit
    parity = (~(addr ^ data ^ cmd)) & LSB_MASK;
    
    return cmdByte |= parity;
}

/*!***************************************************************************** @brief    Write data to register*/eDrvError writeReg(uint8_t addr, uint8_t data){    eDrvError exitStatus = drvUnknownError, drvExStatus;    uint8_t rxData[TRANSACTION_BYTES], txData[TRANSACTION_BYTES];        //Compose command bit, address and parity bit    txData[0] = composeCmdByte(CMD_BIT_WRITE, addr, data);    txData[1] = data;    //Perform transaction with received packet checking    hw_wrap_spiTxRx(txData, rxData, TRANSACTION_BYTES);    drvExStatus = hw_wrap_spiTxRx(txData, rxData, TRANSACTION_BYTES);    if(drvExStatus == drvNoError){        txData[0] = txData[0] >> PARITY_BIT_POS;        if(((rxData[0] & ((~SPI_ERROR_BIT) & BYTE_MASK)) == txData[0]) && (rxData[1] == txData[1]) && ((rxData[0] & SPI_ERROR_BIT) == 0)){            exitStatus = drvNoError;        }else if((rxData[0] & SPI_ERROR_BIT) != 0){            //TO DO: implement errors proccessing            exitStatus = drvHwError;        }    }        return exitStatus;}
/*!***************************************************************************** @brief    Compose command byte of cmd bit, address and parity bit* @param    Commmand bit* @param    6-bit address* @param    Data-to-transmit byte*/uint8_t composeCmdByte(uint8_t cmd, uint8_t addr, uint8_t data){    uint8_t cmdByte, parity;        //Compose command byte    cmdByte = ((addr & ADDRESS_MSK) << PARITY_BIT_POS) | (cmd << CMD_BIT_POS);    //Calculate parity bit    parity = (~(addr ^ data ^ cmd)) & LSB_MASK;        return cmdByte |= parity;}