Potential Bug in STM32Cube SPI routine

[Innomatic]

Posted on June 05, 2016 at 19:15

Hello,

In my senario, a SPI eeprom is connected to a STM32F051, whose SPI module was set to a full duplex master mode. My original code to read a block of data from the eeprom was like this:The problem of this code is that the HAL_SPI_Transmit() leaves data on the RX buffer by default, so that when HAL_SPI_Receive() was executed, 3 bytes of garbage data was introduced at the beginning of the read buffer while the same amount of data was missing at the end.So, I have to flush the Rx buffer before every HAL_SPI_Receive() call.whereThanks, #stm32cube #spi #bug

[Amel NASRI]

Posted on June 08, 2016 at 15:24

Hi lee.sungjune.001,

If the SPI is transmitter, the RXFIFO shouldn't be used.I don't think that the root cause of your problem is the function HAL_SPI_Transmit.You need to more investigate how the 3 bytes remain there.-Mayla-

[Innomatic]

Posted on June 08, 2016 at 16:59

Hi Mayla,

Thanks for the reply. However my understanding is that when SPI is set to full-duplex mode, the RX buffer is always operational regardless of HAL_SPI_Transmit() or HAL_SPI_TransmitReceive() being used.The problem in my case is that the RX buffer was not empty when HAL_SPI_Receive() was called but had un-read garbage data due to previous full-duplex transaction in this case HAL_SPI_Transmit().One obvious solution is not to use HAL_SPI_Transmit() / HAL_SPI_Receive() in full-duplex mode but use HAL_SPI_TransmitReceive() only. But the situation is the same actually since you have to separate your data from the RX buffer whose contents include garbage bytes at the beginning. Thanks,

[matic]

Posted on June 09, 2016 at 00:01

In SPI full-duplex mode transmission and reception are synchronous. When master is sending data on MOSI line along with clocks on CLK line, it is also receiving data on MISO line.

I am not familiar with these two HAL functions, but you definitely should not call them separately.When I want to start data transfer (and receive data from slave), I first set RXDMAEN bit in SPI->CR2 register. Thus, SPI master is ready to receive data. After that I set TXDMAEN bit in SPI->CR2 register. Now, master starts to send data out along with clocks. It is receiving at the same time. (Note: SPI and both DMA channels (Rx, Tx) should be already enabled when setting RXDMAEN and TXDMAEN bits.)When TCIF for Tx in DMA registers is set, all data were sent out. At that point master stops sending clocks too. If amount of data which should be received is equal to amount of data that was transferred, TCIF for Rx in DMA registers is set too.Then you should have all data in your RX buffer.