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Error handling for UART RX with DMA

Question asked by T B on Jan 15, 2018



I am using RX DMA with RX timeout detection (based on Efficiently receive UART data using DMA). Under normal condition, everything works fine, but I have problems with the error handing. My MCU is the F302R8 on the NUCLEO-F302R8.


I have I test case, where I send data on the half baudrate to provoke an UART framing error on the receiver. For example, I send “0xF8, 0x00, 0xFF” and the receiver gets “0x80, 0x00 (framing error) 0x0FE”

Test signal


Now I have two problems:


First problem: DDRE (DMA Disable on Reception Error) does not disable the DMA.
If USART_CR3_DDRE is disabled, I receive only the error free bytes "0x80, 0x0FE". This is as expected.
But if USART_CR3_DDRE is enabled I receive “0x80, 0x00, 0x0FE” and the DMA is not stopped.
Here I would expect to receive only the bytes until the error and that the DMA is disabled.


Second problem: My test sometimes cause a UART Timeout and sometimes not.
Strangely if the UART error interrupt is enabled, then the UART Timeout is set after each block of bytes. (In the ISR I only increasing a counter and clear the framing error.)
Without UART error interrupt not each block of bytes causes a UART Timeout.