2023-07-24 03:09 AM
Hello,
I am using STM32F303RBT on a custom board and am trying to communicate through SPI with LTC6811-1 with code generated through CUBEMX.
I am able to send and receive the data fine when the data is not required to be sent in one burst (LTC6811 can handle pauses between bytes except when it is trying to write I2C data over SPI and then requires tight clocking).
Can the pauses be eliminated by using bare metal for HAL_SPI_TransmitReceive()?
Does someone have a simpler (faster) version of this function?
Below are clock and MOSI signals aforementioned with 15 us pauses between.
The code which calls HAL_SPI_TransmitReceive(...) is also attached.
Pauses between bytes
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Solved! Go to Solution.
2023-07-24 10:24 AM
Thank you for the interest!
I have tried with your suggestion to write the whole array, but with no performance improvement with default CUBE library.
I however managed to shorten the delay between bytes by writing a much simpler version of HAL_SPI_TransmitReceive function (Code below). However, I still have delays between bytes (tried with both using for loops with length 1 and single instruction with whole array and length parameter). I get the pauses between bytes in all four combinations.
Is there an hardware option I need to enable that I'm missing?
Faster SPI_TransmitReceive code:
void HAL_SPI_TransmitReceiveFast(SPI_HandleTypeDef *hspi, uint8_t *pTxData, uint8_t *pRxData, uint16_t Size,
uint32_t Timeout)
{
SPI_TypeDef *SPIx= hspi->Instance;
uint16_t count=Size;
__HAL_SPI_ENABLE(hspi);
while (count--)
{
while ((SPIx->SR & SPI_FLAG_TXE) == 0 || (SPIx->SR & SPI_FLAG_BSY));
*(__IO uint8_t *)&SPIx->DR = *pTxData++;
while ((SPIx->SR & SPI_FLAG_RXNE) == 0 || (SPIx->SR & SPI_FLAG_BSY));
*pRxData++ = *(__IO uint8_t *)&SPIx->DR;
}
}
Slow (Cube MX generated about 20 us pauses):
Slow (STM32 HAL)
Faster version (still with pauses but only 4 us):
Fast
2023-07-24 06:09 AM
so try sending whole array...
HAL_SPI_TransmitReceive(pspi, (uint8_t*)data, &ret_val, len, 5);
2023-07-24 10:24 AM
Thank you for the interest!
I have tried with your suggestion to write the whole array, but with no performance improvement with default CUBE library.
I however managed to shorten the delay between bytes by writing a much simpler version of HAL_SPI_TransmitReceive function (Code below). However, I still have delays between bytes (tried with both using for loops with length 1 and single instruction with whole array and length parameter). I get the pauses between bytes in all four combinations.
Is there an hardware option I need to enable that I'm missing?
Faster SPI_TransmitReceive code:
void HAL_SPI_TransmitReceiveFast(SPI_HandleTypeDef *hspi, uint8_t *pTxData, uint8_t *pRxData, uint16_t Size,
uint32_t Timeout)
{
SPI_TypeDef *SPIx= hspi->Instance;
uint16_t count=Size;
__HAL_SPI_ENABLE(hspi);
while (count--)
{
while ((SPIx->SR & SPI_FLAG_TXE) == 0 || (SPIx->SR & SPI_FLAG_BSY));
*(__IO uint8_t *)&SPIx->DR = *pTxData++;
while ((SPIx->SR & SPI_FLAG_RXNE) == 0 || (SPIx->SR & SPI_FLAG_BSY));
*pRxData++ = *(__IO uint8_t *)&SPIx->DR;
}
}
Slow (Cube MX generated about 20 us pauses):
Slow (STM32 HAL)
Faster version (still with pauses but only 4 us):
Fast
2023-07-24 10:43 AM - edited 2023-07-24 10:45 AM
if you want fastest possible, need to use DMA.
+
what clocks for core + bus ? max. ?
+ optimizer -Ofast or -O2 set ? without optimizer - forget it.
2023-07-24 03:53 PM - edited 2023-07-24 04:10 PM
The TXE flag is set immediately after the Tx byte is sent to the hardware, but your code does not load the next Tx byte until the Rx byte of the previous period is received. With such approach one just cannot get the maximum speed. Instead you should do something like this:
void HAL_SPI_TransmitReceiveFast(SPI_HandleTypeDef *hspi, uint8_t *pTxData, uint8_t *pRxData, uint16_t Size,
uint32_t Timeout)
{
SPI_TypeDef *SPIx = hspi->Instance;
__HAL_SPI_ENABLE(hspi);
while (Size) {
uint32_t rSR = SPIx->SR;
if (rSR & SPI_FLAG_TXE) {
*(volatile uint8_t *)&SPIx->DR = *pTxData++;
}
if (rSR & SPI_FLAG_RXNE) {
*pRxData++ = *(volatile uint8_t *)&SPIx->DR;
--Size;
}
}
while ((SPIx->SR & SPI_FLAG_BSY));
}
@AScha.3 , the DMA doesn't magically make the interface faster, it just frees the CPU from doing data transfers.
2023-07-27 05:22 AM
I managed to get it to work with the because there was the other underlying issue not related to SPI timing. It is working currently with the code above. Also, It is strange that I have yet to see documented code which uses FIFO or something similar Pirahna suggested.
Here is my untested idea:
Fill the TX FIFO with 16 words (or how much the message has). When RX FIFO receives some word read it and, give the TX FIFO the next word if it has any. If the FIFO works properly, there should be no pauses, as the CPU never waits until the message is received without having a new message to send.
void HAL_SPI_TransmitReceiveFast(SPI_HandleTypeDef *hspi, uint8_t *pTxData, uint8_t *pRxData, uint16_t Size, uint32_t Timeout)
{
SPI_TypeDef *SPIx = hspi->Instance;
uint16_t count = Size;
uint16_t txCount = 0;
uint16_t rxCount = 0;
// Enable the SPI peripheral
__HAL_SPI_ENABLE(hspi);
// Fill the TX FIFO initially, up to its depth (16 bytes)
while (txCount < 16 && count > 0)
{
*(__IO uint8_t *)&SPIx->DR = *pTxData++;
txCount++;
count--;
}
// Transmit and receive data in a loop
while (count)
{
// Check if RX FIFO has data to be read
if (SPIx->SR & SPI_FLAG_RXNE)
{
//Read the data
*pRxData++ = *(__IO uint8_t *)&SPIx->DR;
// Add the next data to TxFIFO if it exists
if(txCount<Size)
{
*(__IO uint8_t *)&SPIx->DR = *pTxData++;
txCount++;
count--;
}
}
}
// Wait for the last byte to be received
while ((SPIx->SR & SPI_FLAG_RXNE) == 0);
// Read the last received byte
*pRxData++ = *(__IO uint8_t *)&SPIx->DR;
// Wait until the last data has been sent out before disabling the SPI peripheral
while (SPIx->SR & SPI_FLAG_BSY);
// Disable the SPI peripheral
__HAL_SPI_DISABLE(hspi);
}