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drivers: uart stm32 F4X, F1X, F2X have a sw sequence to clear error flags

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Gives more explanation on uart_stm32_err_check function.
On stm32 F4X, F1X, and F2X, when clearing the usart Error Flag
(PE, ORE, FE, NE), the  LL Clear function applies a software sequence
which reads the usart SR then the usart DR.
Consequently the RXNE flag is affected (cleared) by the
uart_stm32_err_check function call.

Signed-off-by: Francois Ramu <francois.ramu@st.com>
This commit is contained in:
Francois Ramu 2022-01-28 16:52:28 +01:00 • committed by Anas Nashif
commit 860bd87ca9
1 changed files with 20 additions and 4 deletions
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24
drivers/serial/uart_stm32.c
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@ -508,6 +508,10 @@ static int uart_stm32_poll_in(const struct device *dev, unsigned char *c)
LL_USART_ClearFlag_ORE(UartInstance); LL_USART_ClearFlag_ORE(UartInstance);
} }
/*
* On stm32 F4X, F1X, and F2X, the RXNE flag is affected (cleared) by
* the uart_err_check function call (on errors flags clearing)
*/
if (!LL_USART_IsActiveFlag_RXNE(UartInstance)) { if (!LL_USART_IsActiveFlag_RXNE(UartInstance)) {
return -1; return -1;
} }
@ -570,9 +574,10 @@ static int uart_stm32_err_check(const struct device *dev)
USART_TypeDef *UartInstance = UART_STRUCT(dev); USART_TypeDef *UartInstance = UART_STRUCT(dev);
uint32_t err = 0U; uint32_t err = 0U;
/* Check for errors, but don't clear them here. /* Check for errors, then clear them.
* Some SoC clear all error flags when at least * Some SoC clear all error flags when at least
* one is cleared. (e.g. F4X, F1X, and F2X) * one is cleared. (e.g. F4X, F1X, and F2X).
* The stm32 F4X, F1X, and F2X also reads the usart DR when clearing Errors
*/ */
if (LL_USART_IsActiveFlag_ORE(UartInstance)) { if (LL_USART_IsActiveFlag_ORE(UartInstance)) {
err |= UART_ERROR_OVERRUN; err |= UART_ERROR_OVERRUN;
@ -595,7 +600,11 @@ static int uart_stm32_err_check(const struct device *dev)
LL_USART_ClearFlag_LBD(UartInstance); LL_USART_ClearFlag_LBD(UartInstance);
} }
#endif #endif
/* Clearing error :
* the stm32 F4X, F1X, and F2X sw sequence is reading the usart SR
* then the usart DR to clear the Error flags ORE, PE, FE, NE
* --> so is the RXNE flag also cleared !
*/
if (err & UART_ERROR_OVERRUN) { if (err & UART_ERROR_OVERRUN) {
LL_USART_ClearFlag_ORE(UartInstance); LL_USART_ClearFlag_ORE(UartInstance);
} }
@ -669,6 +678,10 @@ static int uart_stm32_fifo_read(const struct device *dev, uint8_t *rx_data,
/* Clear overrun error flag */ /* Clear overrun error flag */
if (LL_USART_IsActiveFlag_ORE(UartInstance)) { if (LL_USART_IsActiveFlag_ORE(UartInstance)) {
LL_USART_ClearFlag_ORE(UartInstance); LL_USART_ClearFlag_ORE(UartInstance);
/*
* On stm32 F4X, F1X, and F2X, the RXNE flag is affected (cleared) by
* the uart_err_check function call (on errors flags clearing)
*/
} }
} }
@ -750,7 +763,10 @@ static void uart_stm32_irq_rx_disable(const struct device *dev)
static int uart_stm32_irq_rx_ready(const struct device *dev) static int uart_stm32_irq_rx_ready(const struct device *dev)
{ {
USART_TypeDef *UartInstance = UART_STRUCT(dev); USART_TypeDef *UartInstance = UART_STRUCT(dev);
/*
* On stm32 F4X, F1X, and F2X, the RXNE flag is affected (cleared) by
* the uart_err_check function call (on errors flags clearing)
*/
return LL_USART_IsActiveFlag_RXNE(UartInstance); return LL_USART_IsActiveFlag_RXNE(UartInstance);
} }