SPI Slave transmit has extra byte at times
I have two STM32F7 processors set up in SPI Master/Slave configuration. When the slave wants to transmit data to the master, it issues an interrupt and the master reads 4 bytes. The first two are the number of data bytes to read, the second two is a command code. The master waits for a go-ahead interrupt, then reads the rest of the bytes.
At times, I'm seeing the first byte of the 4-byte transfer duplicated in the data transfer - thus shifting the bytes by one, and adding one byte to the transfer. This may make more sense by looking at the captures from the logic analyzer. I am using HAL_SPI_Transmit_IT to the master, and HAL_SPI_Receive_IT on the master side to receive the bytes.
The transfer rate is 14 MHz. Slowing the clock down makes no difference.
Using SPI_NSS_PULSE_DISABLE or SPI_NSS_PULSE_ENABLE does not help
On the Master side, using SPI_NSS_HARD_OUTPUT or generating the NSS signal manually makes no difference.
The only thing that seems to help is enforcing a minimum transfer rate of 2ms. In other words, the slave needs to wait 2ms minimum between transfers.
Slave initialization:
/* SPI Port for communications with Master processor
**/
void HAL_SPI_MspInit(SPI_HandleTypeDef* hspi)
{
GPIO_InitTypeDef GPIO_InitStruct;
if(hspi->Instance==SPI1)
{
/* Peripheral clock enable */
__HAL_RCC_SPI1_CLK_ENABLE();
/**SPI1 GPIO Configuration
PA4 ------> SPI1_NSS
PA5 ------> SPI1_SCK
PA6 ------> SPI1_MISO
PA7 ------> SPI1_MOSI
*/
GPIO_InitStruct.Pin = SPI_CS_IN_Pin|SPI_CLK_IN_Pin|SPI_MISO_Pin|SPI_MOSI_Pin;
GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
GPIO_InitStruct.Pull = GPIO_NOPULL;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
GPIO_InitStruct.Alternate = GPIO_AF5_SPI1;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
/* SPI1 interrupt Init */
HAL_NVIC_SetPriority(SPI1_IRQn, 1, 0);
HAL_NVIC_EnableIRQ(SPI1_IRQn);
}
}
/* SPI1 init function */
void MX_SPI1_Init(void)
{
/* SPI1 parameter configuration*/
SPI_SLAVE_1.Instance = SPI1;
SPI_SLAVE_1.Init.Mode = SPI_MODE_SLAVE;
SPI_SLAVE_1.Init.Direction = SPI_DIRECTION_2LINES;
SPI_SLAVE_1.Init.DataSize = SPI_DATASIZE_8BIT;
SPI_SLAVE_1.Init.CLKPolarity = SPI_POLARITY_LOW;
SPI_SLAVE_1.Init.CLKPhase = SPI_PHASE_1EDGE;
SPI_SLAVE_1.Init.NSS = SPI_NSS_HARD_INPUT;
SPI_SLAVE_1.Init.FirstBit = SPI_FIRSTBIT_MSB;
SPI_SLAVE_1.Init.TIMode = SPI_TIMODE_DISABLE;
SPI_SLAVE_1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
SPI_SLAVE_1.Init.CRCPolynomial = 7;
SPI_SLAVE_1.Init.CRCLength = SPI_CRC_LENGTH_DATASIZE;
SPI_SLAVE_1.Init.NSSPMode = SPI_NSS_PULSE_DISABLE;
if (HAL_SPI_Init(&SPI_SLAVE_1) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
}Has anyone seen similar issues with the SPI Slave transfer?
Mark