DK-TM4C129X: DMA mixed peripheral and memory scatter-gather

Hi Charles,

Thanks for the example. I actually continued to think through how to configure scatter-gather for my requirements and came up with something that is working. I'll include the code for reference for anyone else who needs it. I would say this implementation is ping-pong without any processor intervention to reset the DMA channels.

To summarize what the code is doing - Two scatter-gather task lists are configured for buffer A and buffer B; the buffer A task list starts with a peripheral scatter-gather to do the FIFO to buffer A memory transfer, the second task sets a buffer A done flag and the third task transfers the first task of buffer B task list into the primary control structure. The buffer B task list is the similar to the buffer A task list with a few changes; the peripheral scatter-gather transfers to buffer B, the second task set a buffer B done flag and the third task transfers the first task of the buffer A task list into the primary control structure.

First, declare two DMA reload vars and define two task lists, one for each buffer.

// DMA Task used to reload DMA task list
tDMAControlTable dmaADCReloadA;
tDMAControlTable dmaADCReloadB;

// DMA scatter-gather task list for buffer A
tDMAControlTable dmaADCTasksA[3] =
{
    uDMATaskStructEntry(512, UDMA_SIZE_32,
    UDMA_SRC_INC_NONE, (void *)(ADC1_BASE + ADC_O_SSFIFO0),
    UDMA_DST_INC_32, &u32_adc_results_buf_a[0],
    UDMA_ARB_4, UDMA_MODE_PER_SCATTER_GATHER),

    uDMATaskStructEntry(1, UDMA_SIZE_32,
    UDMA_SRC_INC_NONE, &u32_true_flag,
    UDMA_DST_INC_NONE, &u32_chk_adc_buf_a,
    UDMA_ARB_1, UDMA_MODE_MEM_SCATTER_GATHER),

    uDMATaskStructEntry(4, UDMA_SIZE_32,
    UDMA_SRC_INC_32, &dmaADCReloadB,
    UDMA_DST_INC_32, 0,
    UDMA_ARB_4, UDMA_MODE_MEM_SCATTER_GATHER)
};

// DMA scatter-gather task list for buffer B
tDMAControlTable dmaADCTasksB[3] =
{
    uDMATaskStructEntry(512, UDMA_SIZE_32,
    UDMA_SRC_INC_NONE, (void *)(ADC1_BASE + ADC_O_SSFIFO0),
    UDMA_DST_INC_32, &u32_adc_results_buf_b[0],
    UDMA_ARB_4, UDMA_MODE_PER_SCATTER_GATHER),

    uDMATaskStructEntry(1, UDMA_SIZE_32,
    UDMA_SRC_INC_NONE, &u32_true_flag,
    UDMA_DST_INC_NONE, &u32_chk_adc_buf_b,
    UDMA_ARB_1, UDMA_MODE_MEM_SCATTER_GATHER),

    uDMATaskStructEntry(4, UDMA_SIZE_32,
    UDMA_SRC_INC_32, &dmaADCReloadA,
    UDMA_DST_INC_32, 0,
    UDMA_ARB_4, UDMA_MODE_MEM_SCATTER_GATHER)
};

DMA initialization

    // ADC 1 Sequence 0 uDMA Configuration
    MAP_uDMAChannelAssign(UDMA_CH24_ADC1_0); // Assign channel 24 to ADC1 SS0
    MAP_uDMAChannelAttributeEnable(UDMA_SEC_CHANNEL_ADC10, UDMA_ATTR_USEBURST);

    dmaADCTasksA[2].pvDstEndAddr = _pu8_dma_control_table + (sizeof(tDMAControlTable) * (UDMA_SEC_CHANNEL_ADC10 + 1)) - 1;
    dmaADCTasksB[2].pvDstEndAddr = _pu8_dma_control_table + (sizeof(tDMAControlTable) * (UDMA_SEC_CHANNEL_ADC10 + 1)) - 1;

    // Setup scatter gather for buffer B task list
    MAP_uDMAChannelScatterGatherSet(UDMA_SEC_CHANNEL_ADC10, 3, &dmaADCTasksB, true);

    // Copy primary control structure to reload B task structure
    dmaADCReloadB.pvSrcEndAddr = ((tDMAControlTable *)_pu8_dma_control_table)[UDMA_SEC_CHANNEL_ADC10].pvSrcEndAddr;
    dmaADCReloadB.pvDstEndAddr = ((tDMAControlTable *)_pu8_dma_control_table)[UDMA_SEC_CHANNEL_ADC10].pvDstEndAddr;
    dmaADCReloadB.ui32Control = ((tDMAControlTable *)_pu8_dma_control_table)[UDMA_SEC_CHANNEL_ADC10].ui32Control;
    dmaADCReloadB.ui32Spare = ((tDMAControlTable *)_pu8_dma_control_table)[UDMA_SEC_CHANNEL_ADC10].ui32Spare;

    // Setup scatter gather for buffer A task list
    MAP_uDMAChannelScatterGatherSet(UDMA_SEC_CHANNEL_ADC10, 3, &dmaADCTasksA, true);

    // Copy primary control structure to reload A task structure
    dmaADCReloadA.pvSrcEndAddr = ((tDMAControlTable *)_pu8_dma_control_table)[UDMA_SEC_CHANNEL_ADC10].pvSrcEndAddr;
    dmaADCReloadA.pvDstEndAddr = ((tDMAControlTable *)_pu8_dma_control_table)[UDMA_SEC_CHANNEL_ADC10].pvDstEndAddr;
    dmaADCReloadA.ui32Control = ((tDMAControlTable *)_pu8_dma_control_table)[UDMA_SEC_CHANNEL_ADC10].ui32Control;
    dmaADCReloadA.ui32Spare = ((tDMAControlTable *)_pu8_dma_control_table)[UDMA_SEC_CHANNEL_ADC10].ui32Spare;

    // Enable sequence 0
    MAP_uDMAChannelEnable(UDMA_SEC_CHANNEL_ADC10);