Using STM32H743 SPI to transfer large data packets

[KYSoh]

Hello,

I am using the SPI on the STM32H743ZITx as a SPI Master in Full-duplex mode to transfer large data packets (1600 bytes). But instead of seeing the data being transferred in a constant burst, I see it being sent out a byte at a time with gaps in between, apart from a burst at the start of the SPI transaction.

Here is my SPI3 settings in STM32CubeIDE, v1.16.1:

The SPI initialization is the default MX_SPI3_Init() provided by Core/Src/spi.c in STM32CubeIDE.

I am using the interrupt transfer method. My code is as follows:

// TxRx complete callback
void HAL_SPI_TxRxCpltCallback(SPI_HandleTypeDef *hspi)
{
	post_semaphore_from_isr(spi_trans_complete_sem);
}
[...]
// here, size = 1600
spi_transaction(uint8_t * txbuff, uint8_t * rxbuff, uint16_t size)
{
	HAL_StatusTypeDef retval = HAL_ERROR;

	// code to assert SPI CS (GPIO signal)

	retval = HAL_SPI_TransmitReceive_IT(&hspi3, txbuff, rxbuff, size);

	// wait for callback for completion
	get_semaphore(spi_trans_complete_sem, HAL_MAX_DELAY);

	// code to deassert SPI CS (GPIO signal)
	return retval;
}

 This is what I see on the logic analyzer:

I expect the SPI CLK signal to be continuous during the transfer, instead of a byte-by-byte transfer with gaps in between.

What can I do to push up the performance of the SPI transaction?

[Pavel A.]

Look at your SPI interrupt handler. Anything causes delays there?

Use DMA instead of interrupt.

Set data width > 8 bits if possible. (for example if data length is always multiple of 4 bytes, set width 32 bits and move data by 32 bits at once).

 

 

[KYSoh]

> Look at your SPI interrupt handler. Anything causes delays there?

I'm using the STM32CubeIDE generated Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_spi.c file, so the ISRs in use are the standard SPI_RxISR_8BIT and SPI_TxISR_8BIT defined in that file.

 

> Use DMA instead of interrupt.

I did try using DMA, but I was not successful in getting the SPI transaction to work. When I enable DMA for SPI Master, are there other settings that must be modified from the default, like using circular DMA, etc?

 

> Set data width > 8 bits if possible.

I will give this a try.

[gbm]

For SPI, DMA is always a way to go, no matter wow small or bi the packets are. To use DMA, make sure that both SPI interrupt and DMA interrupt are enabled.