MSP432P401R: DMA gather scatter setup question, please clear

Yuliy,

   The "MODE" that you set in the tasks should also be scatter-gather except for the last one which can be basic.  

Please find examples here:

Regards,

Chris

You could do this a couple of different ways.

(1) You could have one channel triggered from RX(CH5) and another from TX (CH0).  This would mean that you would have to manually clear the txifg and then wait for the RX.  The task list triggered from the RX (CH5) would recieve the data based upon the peripheral scatter gather but the next to last byte recieved would use the memory scatter gather so that the next task which starts the transmit sequence would start automatically.  By writing to the TX buf the other dma channel (CH0) would start to move data into the TX as the TXBUF is available.  Please see the previously mentioned demo's on how to mix memory and peripheral scatter-gather.

(2) You could have everything triggered from the RX (CH5).  You would still need to mix the memory and peripheral scatter gather to transition between the RX and TX.  The key is putting in 'dummy' tasks in the TX mechanism so that the DMA does not write to the TXBUF faster then it is actually transmitting data.

Chris

Hello Chris,

you wrote

This would mean that you would have to manually clear the txifg and then wait for the RX.  The task list triggered from the RX (CH5) would recieve the data based upon the peripheral scatter gather but the next to last byte recieved would use the memory scatter gather so that the next task which starts the transmit sequence would start automatically.  By writing to the TX buf the other dma channel (CH0) would start to move data into the TX as the TXBUF is available

Sorry did not get your advise

>This would mean that you would have to manually clear the txifg and then wait for the RX

manually, means CPU, menas no scatter gather automation. right?  

>that the next task which starts the transmit sequence would start automaticallyGood,

that is what I want, question, what channel must I use in 

DMA_setChannelScatterGather? first param?

will investigate examples,
thanks

Thank you Chris,

i will investigate the issue but only at Wendsday, we have a holiday in Germany.

Sorry for delay, I hope I do not make your balance of unanswerwed topics too much...

:-)

Hi Chris,

another small question..

from  ADC DMA example

    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &EUSCI_B2_SPI->RXBUF,
                UDMA_DST_INC_NONE, &dummyRX,
                UDMA_ARB_4, (UDMA_MODE_MEM_SCATTER_GATHER+UDMA_MODE_ALT_SELECT)),
    /* Task2, Clear Chip select */
    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &outputLow,
                UDMA_DST_INC_NONE, &P3->OUT,
                UDMA_ARB_4, (UDMA_MODE_MEM_SCATTER_GATHER+UDMA_MODE_ALT_SELECT)),
    /* Task3, load TX buffer to initiate SPI */
    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &dummyTX,
                UDMA_DST_INC_NONE, &EUSCI_B2_SPI->TXBUF,
                UDMA_ARB_4, (UDMA_MODE_PER_SCATTER_GATHER+UDMA_MODE_ALT_SELECT)),

When we read from periphery (UART) we use  UDMA_MODE_MEM_SCATTER_GATHER

when we write po periphery we use  UDMA_MODE_PER_SCATTER_GATHER

Why? it is clear the second, I do not understand first...Both works with periphery...

Thank you Chris, you really help me.

I hope others also will have good info out of our dialog.

Another small question

I see

Yuli,

    I am glad that this was helpful.  Coming from an MSP430 background I do not find the Scatter-gather very intuitive, but I think that is just because it is new to me.

  There is no reason to use the '+' instead of a logical or.  I think the logical or would be more appropriate in this context.  Moreover, the UDMA_MODE_ALT_SELECT is not needed because by definition the tasks are performed in the alternate channel while the primary channel is used to load the tasks into the alternate in the scatter-gather mode.  In more recent examples this definition is omitted.

Regards,

Chris 

Hi Chris,

have difficulties in implementation of HW pair

MSP432  (UART TX with DMA gather-scatter) -----------> Tiva TM4C129 (UART RX TI Rtos DMA )

test shows following problems

RX receives first TX sending properly, but all subsequent with some amount of garbage. it looks like overlapping... first happens lost 2 or 4 bytes, then rest is overlapping or shifted..

since I expect fixed TX Telegramm size. I see it clearly.. no random bytes but right byte but wrong place. I hope you understand what I mean.

this is my DMA Task array

static DMA_ControlTable dmaControlTablesConfigTX[1] =
{
    DMA_TaskStructEntry(HEADER_LENGTH + CONFIG_PAYLOAD_LENGTH, UDMA_SIZE_8,
                        UDMA_SRC_INC_8, txBuff,
                        UDMA_DST_INC_NONE, &EUSCI_A0->TXBUF,
                        UDMA_ARB_1, UDMA_MODE_BASIC)
};

//this is my DMA set code 

static void prepareDMA_scatter_gather()
{
    MAP_DMA_enableModule();
    MAP_DMA_setControlBase(dmaControlTable);

    MAP_DMA_assignChannel(DMA_CH0_EUSCIA0TX);
    MAP_DMA_assignChannel(DMA_CH5_EUSCIA2RX);
    MAP_DMA_clearInterruptFlag(DMA_CHANNEL_0);
    MAP_DMA_clearInterruptFlag(DMA_CHANNEL_5);

    MAP_DMA_assignInterrupt         (INT_DMA_INT0, DMA_CHANNEL_0);
    MAP_DMA_assignInterrupt         (INT_DMA_INT0, DMA_CHANNEL_5);
    MAP_DMA_enableInterrupt         (INT_DMA_INT0);

    MAP_Interrupt_enableInterrupt   (INT_DMA_INT0);

    MAP_DMA_enableInterrupt         (INT_DMA_ERR);
    MAP_Interrupt_enableInterrupt   (INT_DMA_ERR);
}

//this is IRQ

void DMA_INT0_IRQHandler(void)
{
  const uint32_t dma_status = DMA_getInterruptStatus();

  if(dma_status & (1 << DMA_CHANNEL_0))
  {
      MAP_DMA_disableChannel        (DMA_CHANNEL_0);
      MAP_DMA_clearInterruptFlag    (DMA_CHANNEL_0);
      ch0Fn(true);
  }

  if(dma_status & (1 << DMA_CHANNEL_5))
  {
      MAP_DMA_disableChannel        (DMA_CHANNEL_5);
      MAP_DMA_clearInterruptFlag    (DMA_CHANNEL_5);
      ch5Fn(true);
  }
}

and I send with following code

MAP_DMA_setChannelScatterGather(DMA_CH0_EUSCIA0TX,1,(void*)dmaControlTablesConfigTX,1);
MAP_DMA_enableChannel(DMA_CHANNEL_0);