MSP432P401R: SPI and DMA

What is "nothing"? No SPI activity? DAC output doesn't change?

What DAC? What Example?

For a Tx, the DMA target should be the USCI transmit buffer (e.g. &UCB0TXBUF) and the trigger the interrupt flag (e.g. UCTXIFG). Keep in mind that the DMA will finish before the transaction is done.

Unsolicited: For short (3-byte) transactions over a fast SPI (most of TI's SPI DACs are pretty fast) DMA will overall slow things down.

See also:
e2e.ti.com/.../2828840

Hi Bruce,

I refered following example in my above asked question: (''dma_eusci_spi_loopback '' ). I tested this example just to make sure to see that either DMA is working properly and how it is transferring data from one memory location to other. By using break point, I checked the destination register (which is mentioned as buffer in example) but its all entries remained zero always. What I expect that this destination memory location should get data from source memory location(mentioned as a buffer too), That's why I assumed that may be DMA is not being triggered by SPI.

In my task, I want to speed up SPI (i think it help me to save some time up to 10 usec).
For transmission, I have trasnmitter buffer which has three bytes but my problem is about destination memory location. I got suggestion here by one TI expert that I should store SPI transmission buffer values in one variable and use it as a destination memory address but this will be the same buffer which is a tranmitter buffer (I have DAC161S055 and it needs one byte command and 2-bytes data and I have divided them in the form of three single bytes and transferring them with SPI protocol in the form of one single byte in one turn . I have attached code below too) but I think DAC output is detination memory location and I do not know where output is being storedt.

Note: Just to see code behaviour, I defined one buffer ''test'' as a destination memory location to see either DMA is transferring something but this buffer entries remain zero also always.


SpiTxBuffer[0] = 0x08;
SpiTxBuffer[1] = *((uint8_t*)(&DacValueDigits) + 1);
SpiTxBuffer[2] = *((uint8_t*)(&DacValueDigits));


MAP_DMA_setChannelControl(DMA_CH0_EUSCIB0TX0 | UDMA_PRI_SELECT,
UDMA_SIZE_8 | UDMA_SRC_INC_8 | UDMA_DST_INC_NONE | UDMA_ARB_1);
MAP_DMA_setChannelTransfer(DMA_CH0_EUSCIB0TX0 | UDMA_PRI_SELECT,
UDMA_MODE_BASIC, SpiTxBuffer,
(void *) MAP_SPI_getTransmitBufferAddressForDMA(EUSCI_B0_BASE),test
1);
MAP_DMA_setChannelControl(DMA_CH1_EUSCIB0RX0 | UDMA_PRI_SELECT,
UDMA_SIZE_8 | UDMA_SRC_INC_NONE | UDMA_DST_INC_8 | UDMA_ARB_1);
MAP_DMA_setChannelTransfer(DMA_CH1_EUSCIB0RX0 | UDMA_PRI_SELECT,
UDMA_MODE_BASIC,
test,
1);

Did you install the jumper wires as described (graphically) at the top of the program? Those form a physical loopback from USCI B0 to B1

As Chris explained in the other thread, you can't set any registers in the DAC device. All you can do is send data (with an appropriate command) and ask the DAC to store something. How this is done is described in the DAC data sheet.

To send the data you (or the DMA) store into the SPI transmit buffer (MAP_SPI_getTransmitBufferAddressForDMA()) and the SPI sends the data to the DAC for you.

Hi Bruce,

Yes I did that jumper connection and I tried again today and this example is working fine now.
I want to extend it for my project and I habe only one SPi channel. Is it necessary to use two DMA channels for one SPI ??

Because according to driver library, there should be one channel for one complete transfer.

If you Never plan to receive anything from the DAC, you don't need to use a DMA channel on the receive side. (Indeed, you don't even need to connect the SOMI pin.) Bytes will still be stored in the RXBUF, but they'll be ignored.

I want to move step by step.One more question about connection now, do i need to make physical connection for my project ?  I think no because i just need master transmission and reception.

Can you please draw or just give me hint if I want to use just one channel of DMA.

Many thanks. Because i am beginner in embedded system and may be ask very basic questions too.

Hi Bruce,

I have one more question. Before, I was transferring data through SPI manually. How much, I have understood DMA working, now I do not need that manullay tranfer. DMA will do all this transfer ,is it ??

then why I need interrupr flag of SPI (UCTXIFG ) ?? Please have a look on my code too :


/* Setup the TX transfer characteristics & buffers */
MAP_DMA_setChannelControl(DMA_CH0_EUSCIB0TX0 | UDMA_PRI_SELECT,
UDMA_SIZE_8 | UDMA_SRC_INC_8 | UDMA_DST_INC_NONE | UDMA_ARB_1);
MAP_DMA_setChannelTransfer(DMA_CH0_EUSCIB0TX0 | UDMA_PRI_SELECT,
UDMA_MODE_AUTO, &SpiTxBuffer,
(void *) MAP_SPI_getTransmitBufferAddressForDMA(EUSCI_B0_BASE),
8);

/* Assigning/Enabling Interrupts */
MAP_Interrupt_enableInterrupt(INT_DMA_INT1);
MAP_DMA_enableInterrupt(INT_DMA_INT1);


SpiTxBuffer[0] = 0x08;
SpiTxBuffer[1] = *((uint8_t*)(&DacValueDigits) + 1);
SpiTxBuffer[2] = *((uint8_t*)(&DacValueDigits));
//SpiTxBufferSize = sizeof(SpiTxBuffer)/sizeof(SpiTxBuffer[0]);
//SpiTxBufferPos = 0;

MAP_GPIO_setOutputLowOnPin(GPIO_PORT_P3, GPIO_PIN7);

MAP_GPIO_setOutputLowOnPin(GPIO_PORT_P6, GPIO_PIN0);
//SPI_enableInterrupt(EUSCI_B0_BASE, EUSCI_B_SPI_TRANSMIT_INTERRUPT);

MAP_DMA_enableChannel(0);

void DMA_INT1_IRQHandler(void)
{

isrCounter++;

MAP_DMA_clearInterruptFlag(0);

/* Disable the interrupt to allow execution */
MAP_Interrupt_disableInterrupt(INT_DMA_INT1);
MAP_DMA_disableInterrupt(INT_DMA_INT1);
}

I'm not sure I understand the question. You don't want this:

> //SPI_enableInterrupt(EUSCI_B0_BASE, EUSCI_B_SPI_TRANSMIT_INTERRUPT);

since the UCTXIFG is what is driving the DMA, so you don't want to mess with it.

HI bruce,

I just want to ask you that when DMA will operate with SPI then DMA will transfer the all data in specified location but it will be triggered by SPI every time. (is it the real concept of DMA too ??)

As before, I was using SPI interrrupt to transfer 3 bytes of data (MCU to DAC). My idea is that then I do not need to enable the interrupt of SPI anymore because now DMA is doing all transfer for me. (Please check the follwing code which is defined for above mentioned interrupt )

void EUSCIB0_IRQHandler(void)
{
if(SPI_getInterruptStatus(EUSCI_B0_BASE,EUSCI_B_SPI_TRANSMIT_INTERRUPT))
{
if( SpiTxBufferSize > 0 )
{
//SPI_clearInterruptFlag(EUSCI_B0_BASE, EUSCI_B_SPI_TRANSMIT_INTERRUPT);
SPI_transmitData(EUSCI_B0_BASE,SpiTxBuffer[SpiTxBufferPos]);
SpiTxBufferPos++;
SpiTxBufferSize--;
}
else
{

SpiTxBufferPos = 0;
SpiTxBufferSize = 0;
SPI_disableInterrupt(EUSCI_B0_BASE, EUSCI_B_SPI_TRANSMIT_INTERRUPT);

}
}
}

Hi Bruce,

I am trying to use DMA scatter gather mode for my project now because I think it will help me more. After reading documents, I set up my code but I think I am making mistake in somewhere DMA Interrupt handler.

As, I am not interested to receive data from slave side, is it necessary for me to transfer data  &EUSCI_B1_SPI->RXBUF to any other folder ?? because I want to write 3-byte data and in one task I can transfer maximum 1-byte data. what I did according to my understanding ,i defined source address addition.For that please check following code:

DMA_ControlTable spiDacDmaSeq[TX_TASKS] =
{
    /* Task1, Dummy read RX buffer to clear IFG
    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
                UDMA_DST_INC_NONE, &dummyRX,
                UDMA_ARB_4, (UDMA_MODE_MEM_SCATTER_GATHER+UDMA_MODE_ALT_SELECT)),*/
    /* Task2, Clear Chip select P6.2
    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &outputLow,
                UDMA_DST_INC_NONE, &P6->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, &SpiTxBuffer[0],
                UDMA_DST_INC_NONE, &EUSCI_B1_SPI->TXBUF,
                UDMA_ARB_4, (UDMA_MODE_PER_SCATTER_GATHER+UDMA_MODE_ALT_SELECT)),
    /* Task4, Dummy read RX buffer to clear IFG, wait for RXIFG trigger
    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
                UDMA_DST_INC_NONE, &dummyRX,
                UDMA_ARB_4, (UDMA_MODE_MEM_SCATTER_GATHER+UDMA_MODE_ALT_SELECT)),
    /* Task 5, load TX buffer to initiate SPI */
    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &SpiTxBuffer[1],
                UDMA_DST_INC_8, &EUSCI_B1_SPI->TXBUF,
                UDMA_ARB_4, (UDMA_MODE_PER_SCATTER_GATHER+UDMA_MODE_ALT_SELECT)),
    /*
     * Task 6, Dummy read RX buffer to clear IFG
     * This delay ensures that the chip select happens after the last byte is transmitted

    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
                UDMA_DST_INC_NONE, &dummyRX,
                UDMA_ARB_4, (UDMA_MODE_MEM_SCATTER_GATHER+UDMA_MODE_ALT_SELECT)),
     /* Task 7, load TX buffer to initiate SPI */
   DMA_TaskStructEntry(1, UDMA_SIZE_8,
                 UDMA_SRC_INC_NONE, &SpiTxBuffer[2],
                 UDMA_DST_INC_16, &EUSCI_B1_SPI->TXBUF,
                 UDMA_ARB_4, (UDMA_MODE_BASIC))
     /* Task 8, set GPIO, chip select
    DMA_TaskStructEntry(1, UDMA_SIZE_8,
                UDMA_SRC_INC_NONE, &DAC_CS,
                UDMA_DST_INC_NONE, &P6->OUT,
                UDMA_ARB_4, UDMA_MODE_BASIC)*/
};

I defer to the Driverlib Wizards on this one. I am familiar with scatter/gather, but not the Driverlib model for it.
-------------------------------
If you don't care about the Rx data, you don't need to move it anywhere. The Rx side will overrun, but you can ignore it.

Good morning Chris,

Thank you for detail explanation. As, I am controlling chip select manually which I have defined in my code so I do not need to pay attention to chip select . I am using channel 0 and its triggering source is eUSCI_B0_TX0 (Using eUSCI_B0 module). In scatter-gather mode , what I need to consider just following parameters: (Please make me correct here ,if something is missing)
1) task table (code mentioned below)
2) one dma channel ( channel 0 defined)
3) one dma interrupt (MAP_DMA_assignInterrupt(DMA_INT1, 0))

I have following questions :

1) how to assign channel number ?? ( I did like that (MAP_DMA_assignChannel(DMA_CH0_EUSCIB0TX0)) )
2) how to declare scatter-gather mode command ?? ( I did like that DMA_setChannelScatterGather(DMA_CH0_EUSCIB0TX0,TX_TASKS,(void*)&spiDacDmaSeq,1))

On debugging this code, SCLk remained zero and it indicates that SPI is unable to trigger dma and moreover I defined one dummyRX ( for counter check to see if DMA is working or not ) but it is not getting any value to too.

************************************************************************************
/* DMA Control Table*/
#if defined(__TI_COMPILER_VERSION__)
#pragma DATA_ALIGN(controlTable, 1024)
#elif defined(__IAR_SYSTEMS_ICC__)
#pragma data_alignment=1024
#elif defined(__GNUC__)
__attribute__ ((aligned (1024)))
#elif defined(__CC_ARM)
__align(1024)
#endif
#define TX_TASKS 6
uint8_t controlTable[16];

********************Task List**********************

DMA_ControlTable spiDacDmaSeq[TX_TASKS] =
{
/*Task1, Dummy read RX buffer to clear IFG */
DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
UDMA_DST_INC_NONE, &dummyRX,
UDMA_ARB_4, (UDMA_MODE_MEM_SCATTER_GATHER)),
/* Task3, load TX buffer to initiate SPI */
DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &SpiTxBuffer[0],
UDMA_DST_INC_NONE, &EUSCI_B1_SPI->TXBUF,
UDMA_ARB_4, (UDMA_MODE_PER_SCATTER_GATHER)),
/* Task4, Dummy read RX buffer to clear IFG, wait for RXIFG trigger */
DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
UDMA_DST_INC_NONE, &dummyRX,
UDMA_ARB_4, (UDMA_MODE_MEM_SCATTER_GATHER)),
/* Task 5, load TX buffer to initiate SPI */
DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &SpiTxBuffer[1],
UDMA_DST_INC_NONE, &EUSCI_B1_SPI->TXBUF,
UDMA_ARB_4, (UDMA_MODE_PER_SCATTER_GATHER)),
/*
* Task 6, Dummy read RX buffer to clear IFG
* This delay ensures that the chip select happens after the last byte is transmitted
*/
DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
UDMA_DST_INC_NONE, &dummyRX,
UDMA_ARB_4, (UDMA_MODE_MEM_SCATTER_GATHER)),
/* Task 7, load TX buffer to initiate SPI */
DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &SpiTxBuffer[2],
UDMA_DST_INC_NONE, &EUSCI_B1_SPI->TXBUF,
UDMA_ARB_4, (UDMA_MODE_AUTO)),

};

**********************************main code******************
MAP_DMA_assignChannel(DMA_CH0_EUSCIB0TX0);
MAP_DMA_assignInterrupt(DMA_INT1, 0);
MAP_Interrupt_enableInterrupt(INT_DMA_INT1);
MAP_Interrupt_disableSleepOnIsrExit();
********************************************************************
MAP_DMA_setChannelScatterGather(DMA_CH0_EUSCIB0TX0,TX_TASKS,(void*)&spiDacDmaSeq,1);
MAP_DMA_enableChannel(DMA_CH0_EUSCIB0TX0);

SPI_enableInterrupt(EUSCI_B0_BASE, EUSCI_A_SPI_RECEIVE_INTERRUPT);

Hi Chris,

Thanks for your explantation, I throughly understand the recommended example and tried to implement it in my case. According to my understanding ,it should work but on debugging this , MOSI and SIMO are not moving still and resulting same result which I have before. It would be great if you just have a look on my code because I think that I am having issues somewhere SPI_Interrupt (may be). many thanks for your support throughout my theses .
/*********************** Configuring DMA module *****************************************/
MAP_DMA_enableModule();
MAP_DMA_setControlBase(controlTable);
MAP_DMA_assignChannel(DMA_CH0_EUSCIB0TX0);
MAP_DMA_assignInterrupt(DMA_INT1, 0);


/****************************declaration*****************/

MAP_DMA_setChannelScatterGather(DMA_CH0_EUSCIB0TX0,TX_TASKS,(void*)&spiDacDmaSeq[0],0);
MAP_DMA_clearInterruptFlag(DMA_CH0_EUSCIB0TX0 & 0x0F);
MAP_DMA_enableChannel(0);
EUSCI_B0_SPI->IFG |= EUSCI_B_IFG_RXIFG0;

SPI_enableInterrupt(EUSCI_B0_BASE, EUSCI_B_SPI_RECEIVE_INTERRUPT); /* main SPI interrupt */
/* Assigning/Enabling Interrupts*/
MAP_DMA_enableInterrupt(INT_DMA_INT1);
MAP_Interrupt_enableInterrupt(INT_DMA_INT1);
MAP_Interrupt_disableSleepOnIsrExit();
**************************task list********************
DMA_ControlTable spiDacDmaSeq[TX_TASKS] =
{
/*Task1, Dummy read RX buffer to clear IFG */

DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
UDMA_DST_INC_NONE, &dummyRX,
UDMA_ARB_1, (UDMA_MODE_MEM_SCATTER_GATHER)),

/* Task3, load TX buffer to initiate SPI */

DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &SpiTxBuffer[0],
UDMA_DST_INC_NONE, &EUSCI_B1_SPI->TXBUF,
UDMA_ARB_1, (UDMA_MODE_PER_SCATTER_GATHER)),

/* Task4, Dummy read RX buffer to clear IFG, wait for RXIFG trigger */

DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
UDMA_DST_INC_NONE, &dummyRX,
UDMA_ARB_1, (UDMA_MODE_MEM_SCATTER_GATHER)),

/* Task 5, load TX buffer to initiate SPI */

DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &SpiTxBuffer[1],
UDMA_DST_INC_NONE, &EUSCI_B1_SPI->TXBUF,
UDMA_ARB_1, (UDMA_MODE_PER_SCATTER_GATHER)),
/*
* Task 6, Dummy read RX buffer to clear IFG

DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &EUSCI_B1_SPI->RXBUF,
UDMA_DST_INC_NONE, &dummyRX,
UDMA_ARB_1, (UDMA_MODE_MEM_SCATTER_GATHER)),

/* Task 7, load TX buffer to initiate SPI */

DMA_TaskStructEntry(1, UDMA_SIZE_8,
UDMA_SRC_INC_NONE, &SpiTxBuffer[2],
UDMA_DST_INC_NONE, &EUSCI_B1_SPI->TXBUF,
UDMA_ARB_1, (UDMA_MODE_AUTO)),

};

Thank you Chris and Bruce, I have solved DMA problem. I used scather gather technique which helped me to speed up spi and am able to save 10us time. I got the similar result with spi-loop back technique also. Once again , thank you so much for your support througout my theses. :)

regards,
Hasan