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cpu/stm32: Fix uart_init()

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- Make use of the fact that gpio_init_af() does not need prior call to
  gpio_init() for all STM32 families anymore and drop call to gpio_init()
- Initialize the UART periph first, before initializing the pins
    - While uninitialized, the UART periph will send signal LOW to TXD. This
      results in a start bit being picked up by the other side.
    - Instead, we do not connect the UART periph to the pins until it is
      initialized, so that the TXD level will already be HIGH when the pins
      are attached.
    - This results in no more garbage being send during initialization
This commit is contained in:
Marian Buschsieweke 2020-07-05 22:57:11 +02:00
parent 73c9161517
commit aec9eb7f6a
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GPG Key ID: 61F64C6599B1539F
1 changed files with 6 additions and 5 deletions
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11
cpu/stm32/periph/uart.c
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@ -117,9 +117,6 @@ static inline void uart_init_cts_pin(uart_t uart)
static inline void uart_init_pins(uart_t uart, uart_rx_cb_t rx_cb)
{
/* configure TX pin */
gpio_init(uart_config[uart].tx_pin, GPIO_OUT);
/* set TX pin high to avoid garbage during further initialization */
gpio_set(uart_config[uart].tx_pin);
#ifdef CPU_FAM_STM32F1
gpio_init_af(uart_config[uart].tx_pin, GPIO_AF_OUT_PP);
#else
@ -172,8 +169,6 @@ int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
tsrb_init(&uart_tx_rb[uart], uart_tx_rb_buf[uart], UART_TXBUF_SIZE);
#endif
uart_init_pins(uart, rx_cb);
uart_enable_clock(uart);
/* reset UART configuration -> defaults to 8N1 mode */
@ -199,6 +194,12 @@ int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
uart_init_usart(uart, baudrate);
#endif
/* Attach pins to enabled UART periph. Note: It is important that the UART
* interface is configured prior to attaching the pins, as otherwise the
* signal level flickers during initialization resulting in garbage being
* sent. */
uart_init_pins(uart, rx_cb);
/* enable RX interrupt if applicable */
if (rx_cb) {
NVIC_EnableIRQ(uart_config[uart].irqn);