ecSPI Problem sending number of bytes which is not dividable by 4

[peterw]

I’m a bit confused what’s going on with the SPI on the i.MX6. Using the SPI driver from the Freescale SDK I tried to send 10 bytes from the master to the slave.

I just build up a test scenario where the master sends the 10 bytes and with a logic analyzer the MOSI is checked.

Sending data is 0xA0 to 0xA9 and the result in the logic analyzer is:

0xA1 0xA0 0xA7 0xA6 0xA5 0xA4 0x00 0x00 0xA9 0xA8

So in that case the 0xA3 0xA2 at the beginning are missing.

As I send a number of bytes which is dividable by 4, there is no problem.

I can expect that if the number of bytes is not dividable by 4 the last bytes are filled up. But as I can see there are 2 byes missing in the first 4 byte block.

It’s not as easy to explain the problem, so if there are any questions about this scenario….

Thanks for any hints.

[alejandrolozan1]

Hi,

I have not checked if that is something that can be changed in the module configuration but to overcome that, I created the below function that sorts the data so the ECSPI module sends it correctly.

u8 __attribute__ ((aligned(4))) g_spi_bcm89501_tx_buf[SPI_BCM_XFER_SZ];

u8 __attribute__ ((aligned(4))) g_spi_bcm89501_rx_buf[SPI_BCM_XFER_SZ];

int spi_XXX_xfer(unsigned char * u8ptrTx,unsigned char * u8ptrRx, int length)

{

        int i;

        int byteiterations, currentiteration;

        unsigned char * u8ptrStartTx = u8ptrTx;

        unsigned char * u8ptrStartRx = u8ptrRx;

        int ByteOffset;

        int nbytesoffset;

        ByteOffset = length % 4;

        nbytesoffset = 4 -  ByteOffset;

        if(ByteOffset == 0)

        {

                nbytesoffset = 0;

        }

        /*Get remaining of data*/

        if(u8ptrTx != NULL)

        {

                u8ptrTx = u8ptrTx + ByteOffset;

                currentiteration = 1;

                byteiterations = length/4;

                while( currentiteration <=byteiterations)

                {

                        i = 4 * currentiteration++;

                        g_spi_bcm89501_tx_buf[i + 3] = *u8ptrTx++;

                        g_spi_bcm89501_tx_buf[i + 2] = *u8ptrTx++;

                        g_spi_bcm89501_tx_buf[i + 1] = *u8ptrTx++;

                        g_spi_bcm89501_tx_buf[i]     = *u8ptrTx++;

                }

                /*point to beginnig of frame*/

                u8ptrTx = u8ptrStartTx;

                /*Copy the remainning bytes, they are the first ones*/

                for(i = 3 ; i >= nbytesoffset ; i--)

                {

                        g_spi_bcm89501_tx_buf[i - nbytesoffset] = *u8ptrTx++;

                }

        }

        /*Begin Transfer*/

        imx_ecspi_xfer(&imx_spi_bcm89501, g_spi_bcm89501_tx_buf, g_spi_bcm89501_rx_buf, (length) * 8);

        /*Copy data from spi driver*/

        if(u8ptrRx != NULL)

        {

                u8ptrRx = u8ptrRx + ByteOffset;

                currentiteration = 1;

                byteiterations = length/4;

                while( currentiteration <=byteiterations)

                {

                        i = 4 * currentiteration++;

                        *u8ptrRx++ = g_spi_bcm89501_rx_buf[i + 3];

                        *u8ptrRx++ = g_spi_bcm89501_rx_buf[i + 2];

                        *u8ptrRx++ = g_spi_bcm89501_rx_buf[i + 1];

                        *u8ptrRx++ = g_spi_bcm89501_rx_buf[i];

                }

                /*point to beginnig of frame*/

                u8ptrRx = u8ptrStartRx;

                /*Copy the remainning bytes, they are the first ones*/

                for(i = 3 ; i >= nbytesoffset ; i--)

                {

                        *u8ptrRx++ = g_spi_bcm89501_rx_buf[i - nbytesoffset];

                }

        }

        return 0;

}

I hope you find that useful.

/Alejandro

[peterw · Accepted solution]

Hi,

this "workaround" works fine. Thanks!