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STM32F7: add warning for RXDMA + IFLOWCONTROL combination 

Combination of RXDMA + IFLOWCONTROL does not work as one might expect.
Since RXDMA uses circular DMA-buffer, DMA will always keep reading new
data from USART peripheral even if DMA buffer underruns. Thus this
combination only does following: RTS is asserted on USART setup and
deasserted on shutdown and does not perform actual RTS flow-control.

Data loss can be demonstrated by doing long up_mdelay inside irq
critical section and feeding data to RXDMA+IFLOWCONTROL UART.
This commit is contained in:
Jussi Kivilinna 2017-04-06 08:47:45 -06:00 committed by Gregory Nutt
parent e2702cbe4e
commit 0aa52d98a2
1 changed files with 40 additions and 0 deletions
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40
arch/arm/src/stm32f7/stm32_serial.c
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@ -218,6 +218,46 @@
#ifdef USE_SERIALDRIVER
#ifdef HAVE_UART
/* Warnings for potentially unsafe configuration combinations. */
/* Combination of RXDMA + IFLOWCONTROL does not work as one might expect.
* Since RXDMA uses circular DMA-buffer, DMA will always keep reading new
* data from USART peripheral even if DMA buffer underruns. Thus this
* combination only does following: RTS is asserted on USART setup and
* deasserted on shutdown and does not perform actual RTS flow-control.
*/
#if defined(CONFIG_USART1_RXDMA) && defined(CONFIG_USART1_IFLOWCONTROL)
# warning "RXDMA and IFLOWCONTROL both enabled for USART1. \
This combination can lead to data loss."
#endif
#if defined(CONFIG_USART2_RXDMA) && defined(CONFIG_USART2_IFLOWCONTROL)
# warning "RXDMA and IFLOWCONTROL both enabled for USART2. \
This combination can lead to data loss."
#endif
#if defined(CONFIG_USART3_RXDMA) && defined(CONFIG_USART3_IFLOWCONTROL)
# warning "RXDMA and IFLOWCONTROL both enabled for USART3. \
This combination can lead to data loss."
#endif
#if defined(CONFIG_USART6_RXDMA) && defined(CONFIG_USART6_IFLOWCONTROL)
# warning "RXDMA and IFLOWCONTROL both enabled for USART6. \
This combination can lead to data loss."
#endif
#if defined(CONFIG_UART7_RXDMA) && defined(CONFIG_UART7_IFLOWCONTROL)
# warning "RXDMA and IFLOWCONTROL both enabled for UART7. \
This combination can lead to data loss."
#endif
#if defined(CONFIG_UART8_RXDMA) && defined(CONFIG_UART8_IFLOWCONTROL)
# warning "RXDMA and IFLOWCONTROL both enabled for UART8. \
This combination can lead to data loss."
#endif
/****************************************************************************
* Private Types
****************************************************************************/