Question
Why LL SPI Receive DMA request generate clocks?
I use a ADS7056 temperature sensor. I want to read the temperature via SPI and DMA.
To do this, I have to set the CS low, generate 18 clocks, set the CS high again.
Unfortunately I haven't found a configuration that works with the LL drivers yet.
To generate the 18 clock, I execute a "dummy" LL_SPI_EnableDMAReq_TX(SPI2);
So far so good.
To read the data from the sensor i perform a LL_SPI_EnableDMAReq_RX(SPI2)
But this request generate another 18 clock.
On the other hand, wenn i execute only LL_SPI_EnableDMAReq_RX(SPI) no clocks are generated.
SPI Settings:
SPI_InitStruct.TransferDirection = LL_SPI_FULL_DUPLEX;
SPI_InitStruct.Mode = LL_SPI_MODE_MASTER;
SPI_InitStruct.DataWidth = LL_SPI_DATAWIDTH_9BIT;
SPI_InitStruct.ClockPolarity = LL_SPI_POLARITY_LOW;
SPI_InitStruct.ClockPhase = LL_SPI_PHASE_2EDGE;
SPI_InitStruct.NSS = LL_SPI_NSS_SOFT;
SPI_InitStruct.BaudRate = LL_SPI_BAUDRATEPRESCALER_DIV8;
SPI_InitStruct.BitOrder = LL_SPI_MSB_FIRST;
SPI_InitStruct.CRCCalculation = LL_SPI_CRCCALCULATION_DISABLE;
SPI_InitStruct.CRCPoly = 7;
LL_SPI_Init(SPI2, &SPI_InitStruct);
LL_SPI_SetStandard(SPI2, LL_SPI_PROTOCOL_MOTOROLA);
LL_SPI_DisableNSSPulseMgt(SPI2);/** Dummy variable to send data over SPI */
uint8_t spi_TxDummy[4] = { 0 };
/** Receive data over SPI */
uint8_t spi_RxBuffer[4] = { 0 };
...
/* Set RXNE Bit when Receive 16bit (9bit from ADS7056) */
LL_SPI_SetRxFIFOThreshold(spi_hw_settings.SPI_Interface, LL_SPI_RX_FIFO_TH_HALF);
/* Configure DMA TX settings */
LL_DMA_ConfigTransfer(DMA1, LL_DMA_CHANNEL_5, LL_DMA_DIRECTION_MEMORY_TO_PERIPH |
LL_DMA_PRIORITY_HIGH | LL_DMA_MODE_NORMAL |
LL_DMA_PERIPH_NOINCREMENT | LL_DMA_MEMORY_INCREMENT |
LL_DMA_PDATAALIGN_BYTE | LL_DMA_PDATAALIGN_BYTE);
LL_DMA_ConfigAddresses(DMA1, LL_DMA_CHANNEL_5, (uint32_t)spi_TxDummy, LL_SPI_DMA_GetRegAddr(SPI2),
LL_DMA_GetDataTransferDirection(DMA1, LL_DMA_CHANNEL_5));
LL_DMA_SetDataLength(DMA1, LL_DMA_CHANNEL_5, sizeof(spi_TxDummy)/sizeof(spi_TxDummy[0]));
/* Equal to "LL_DMA_SetPeriphRequest(...)" but there is a bug in the LL library */
DMA1_CSELR->CSELR |= 1 << DMA_CSELR_C5S_Pos;
/* Configure DMA RX settings */
LL_DMA_ConfigTransfer(DMA1, LL_DMA_CHANNEL_4, LL_DMA_DIRECTION_PERIPH_TO_MEMORY |
LL_DMA_PRIORITY_LOW | LL_DMA_MODE_NORMAL|
LL_DMA_PERIPH_NOINCREMENT | LL_DMA_MEMORY_INCREMENT |
LL_DMA_PDATAALIGN_BYTE | LL_DMA_PDATAALIGN_BYTE);
LL_DMA_ConfigAddresses(DMA1, LL_DMA_CHANNEL_4, (uint32_t)spi_RxBuffer, LL_SPI_DMA_GetRegAddr(SPI2),
LL_DMA_GetDataTransferDirection(DMA1, LL_DMA_CHANNEL_4));
LL_DMA_SetDataLength(DMA1, LL_DMA_CHANNEL_4, sizeof(spi_RxBuffer)/sizeof(spi_RxBuffer[0]));
/* Equal to "LL_DMA_SetPeriphRequest(...)" but there is a bug in the LL library */
DMA1_CSELR->CSELR |= 1 << DMA_CSELR_C4S_Pos;
/* Enable DMA RX request */
LL_DMA_EnableChannel(DMA1, LL_DMA_CHANNEL_5);
LL_SPI_EnableDMAReq_RX(spi_hw_settings.SPI_Interface);
/* Enable DMA TX request */
LL_DMA_EnableChannel(DMA1, LL_DMA_CHANNEL_4);
LL_SPI_EnableDMAReq_TX(spi_hw_settings.SPI_Interface);
/* Set CS low */
LL_GPIO_ResetOutputPin(spi_hw_settings.GPIO_Port, spi_hw_settings.GPIO_Pin);
LL_SPI_Enable(spi_hw_settings.SPI_Interface);
/* Wait until DMA dummy transfer complete */
while (!LL_DMA_IsActiveFlag_TC5(DMA1)) {}
/* Wait until clock generation complete */
while (LL_SPI_IsActiveFlag_BSY(spi_hw_settings.SPI_Interface)) {}
LL_SPI_Disable(spi_hw_settings.SPI_Interface);
/* Set CS high again */
LL_GPIO_SetOutputPin(spi_hw_settings.GPIO_Port, spi_hw_settings.GPIO_Pin);So what can i do to generate 18 clock and do an DMA SPI read?