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K60: Flush of SPI and SPI DMA not removing bytes already in the hardware registers.

Question asked by Simon Pearson on Dec 9, 2014
Latest reply on Apr 23, 2015 by Simon Pearson

I am running an SPISlave_LDD connected to a DMA_LDD.  At some point I receive a bad packet and my protocol flushes the system:

 

void SPIDriver_flush(void) {

    IPIFSpi2Tx_CancelTransfer(Spi2Tx_DeviceData);

    SS1_CancelBlockTransmission(SS1_DeviceData);

 

    IPIFSpi2Rx_CancelTransfer(Spi2Rx_DeviceData);

    SS1_CancelBlockReception(SS1_DeviceData);

 

...

}

Without getting into too much detail, my sentinel is 0xC3 (the first char sent by the SPI master when looking at the waveform on an oscilloscope) which is delayed by two chars.

[000]  0x0C 0x0C 0xC3 0x00 0xA4 0x98 0x00 0x00 0x00 0x00 0x0C 0x0C 0x0C 0x0C 0x0C 0x0C

 

The two chars seem to be coming from the SPI and DMA hardware registers:

 

Adding a read of the SPI register after the flush removes one of the two errant chars:

void SPIDriver_flush(void) {

    IPIFSpi2Tx_CancelTransfer(Spi2Tx_DeviceData);

    SS1_CancelBlockTransmission(SS1_DeviceData);

 

    IPIFSpi2Rx_CancelTransfer(Spi2Rx_DeviceData);

    SS1_CancelBlockReception(SS1_DeviceData);

 

   int x =  (volatile)SPI2_POPR;

...

}

 

[000]  0x0C 0xC3 0x00 0xA4 0x98 0x00 0x00 0x00 0x00 0x0C 0x0C 0x0C 0x0C 0x0C 0x0C  0x0C

 

Adding a DMA read of two characters after the flush removes both errant chars:

 

void SPIDriver_flush(void) {

    IPIFSpi2Tx_CancelTransfer(IPIFSpi2Tx_DeviceData);

    SS1_CancelBlockTransmission(SS1_DeviceData);

 

    IPIFSpi2Rx_CancelTransfer(IPIFSpi2Rx_DeviceData);

    SS1_CancelBlockReception(SS1_DeviceData);

 

    int x =  (volatile)SPI2_POPR;

    unsigned char foo[2];

    (void)IPIFSpi2Rx_SetDestinationAddress(Spi2Rx_DeviceData, (LDD_DMA_TAddress)&foo);

    (void)IPIFSpi2Rx_SetDestinationTransferSize(Spi2Rx_DeviceData, (LDD_DMA_TTransferSize)2)

    (void)IPIFSpi2Rx_EnableChannel(Spi2Rx_DeviceData);

...

}

 

[000]  0xC3 0x00 0xA4 0x98 0x00 0x00 0x00 0x00 0x0C 0x0C 0x0C 0x0C 0x0C 0x0C  0x0C 0x0C

 

 

Is there a better way to ensure a complete flush of the hardware or is this an appropriate solution?

 

Thanks in advance,

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