We are trying to implement the SPI interface on a STM32G070 MCU using DMA and no interrupts. MOSI MISO and SCLK all work fine, but the NSS signal does not behave the way we want it to. What we need is a precise change from 1 to 0 signaling the start of the transmission and right after the transmission is finished we need the immediate change from 0 to 1. What do we need to do to get this behavior?
SPI1 registers:
CR1: 0x0105
CR2: 0x1704
SPI and DMA init:
LL_SPI_InitTypeDef SPI_InitStruct = {0};
LL_GPIO_InitTypeDef GPIO_InitStruct = {0};
/* Peripheral clock enable */
LL_APB2_GRP1_EnableClock(LL_APB2_GRP1_PERIPH_SPI1);
LL_IOP_GRP1_EnableClock(LL_IOP_GRP1_PERIPH_GPIOA);
LL_IOP_GRP1_EnableClock(LL_IOP_GRP1_PERIPH_GPIOB);
LL_AHB1_GRP1_EnableClock(LL_AHB1_GRP1_PERIPH_DMA1);
/** SPI1 GPIO Configuration +**/
GPIO_InitStruct.Pin = SPI_SCK_PIN;
GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;
GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
GPIO_InitStruct.Pull = LL_GPIO_PULL_NO;
GPIO_InitStruct.Alternate = LL_GPIO_AF_0;
LL_GPIO_Init(SPI_SCK_GPIO_Port, &GPIO_InitStruct);
GPIO_InitStruct.Pin = SPI_MOSI_PIN;
GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;
GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
GPIO_InitStruct.Pull = LL_GPIO_PULL_NO;
GPIO_InitStruct.Alternate = LL_GPIO_AF_0;
LL_GPIO_Init(SPI_MOSI_GPIO_Port, &GPIO_InitStruct);
GPIO_InitStruct.Pin = SPI_MISO_PIN;
GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_LOW;
GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
GPIO_InitStruct.Pull = LL_GPIO_PULL_NO;
GPIO_InitStruct.Alternate = LL_GPIO_AF_0;
LL_GPIO_Init(SPI_MISO_GPIO_Port, &GPIO_InitStruct);
GPIO_InitStruct.Pin = SPI_NSS_PIN;
GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_LOW;
GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
GPIO_InitStruct.Pull = LL_GPIO_PULL_NO;
GPIO_InitStruct.Alternate = LL_GPIO_AF_0;
LL_GPIO_Init(SPI_NSS_GPIO_Port, &GPIO_InitStruct);
LL_GPIO_SetOutputPin(SPI_NSS_GPIO_Port, SPI_NSS_PIN);
/* SPI1 DMA Init */
/* SPI1_RX Init */
LL_DMA_SetPeriphRequest(DMA1, LL_DMA_CHANNEL_1, LL_DMAMUX_REQ_SPI1_RX);
LL_DMA_SetDataTransferDirection(DMA1, LL_DMA_CHANNEL_1, LL_DMA_DIRECTION_PERIPH_TO_MEMORY);
LL_DMA_SetChannelPriorityLevel(DMA1, LL_DMA_CHANNEL_1, LL_DMA_PRIORITY_LOW);
LL_DMA_SetMode(DMA1, LL_DMA_CHANNEL_1, LL_DMA_MODE_NORMAL);
LL_DMA_SetPeriphIncMode(DMA1, LL_DMA_CHANNEL_1, LL_DMA_PERIPH_NOINCREMENT);
LL_DMA_SetMemoryIncMode(DMA1, LL_DMA_CHANNEL_1, LL_DMA_MEMORY_INCREMENT);
LL_DMA_SetPeriphSize(DMA1, LL_DMA_CHANNEL_1, LL_DMA_PDATAALIGN_BYTE);
LL_DMA_SetMemorySize(DMA1, LL_DMA_CHANNEL_1, LL_DMA_MDATAALIGN_BYTE);
/* SPI1_TX Init */
LL_DMA_SetPeriphRequest(DMA1, LL_DMA_CHANNEL_2, LL_DMAMUX_REQ_SPI1_TX);
LL_DMA_SetDataTransferDirection(DMA1, LL_DMA_CHANNEL_2, LL_DMA_DIRECTION_MEMORY_TO_PERIPH);
LL_DMA_SetChannelPriorityLevel(DMA1, LL_DMA_CHANNEL_2, LL_DMA_PRIORITY_LOW);
LL_DMA_SetMode(DMA1, LL_DMA_CHANNEL_2, LL_DMA_MODE_NORMAL);
LL_DMA_SetPeriphIncMode(DMA1, LL_DMA_CHANNEL_2, LL_DMA_PERIPH_NOINCREMENT);
LL_DMA_SetMemoryIncMode(DMA1, LL_DMA_CHANNEL_2, LL_DMA_MEMORY_INCREMENT);
LL_DMA_SetPeriphSize(DMA1, LL_DMA_CHANNEL_2, LL_DMA_PDATAALIGN_BYTE);
LL_DMA_SetMemorySize(DMA1, LL_DMA_CHANNEL_2, LL_DMA_MDATAALIGN_BYTE);
/* SPI1 parameter configuration*/
SPI_InitStruct.TransferDirection = LL_SPI_FULL_DUPLEX;
SPI_InitStruct.Mode = LL_SPI_MODE_MASTER;
SPI_InitStruct.DataWidth = LL_SPI_DATAWIDTH_8BIT;
SPI_InitStruct.ClockPolarity = LL_SPI_POLARITY_LOW;
SPI_InitStruct.ClockPhase = LL_SPI_PHASE_2EDGE;
SPI_InitStruct.NSS = LL_SPI_NSS_HARD_OUTPUT;
SPI_InitStruct.BaudRate = LL_SPI_BAUDRATEPRESCALER_DIV2;
SPI_InitStruct.BitOrder = LL_SPI_MSB_FIRST;
SPI_InitStruct.CRCCalculation = LL_SPI_CRCCALCULATION_DISABLE;
SPI_InitStruct.CRCPoly = 7;
LL_SPI_Init(SPI1, &SPI_InitStruct);
LL_SPI_SetStandard(SPI1, LL_SPI_PROTOCOL_MOTOROLA);
LL_SPI_DisableNSSPulseMgt(SPI1);
