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cpu/stm32: Fix garbage on UART init #14426

Merged
merged 2 commits into from
Jul 15, 2020
Merged

cpu/stm32: Fix garbage on UART init #14426

merged 2 commits into from
Jul 15, 2020

Commits on Jul 15, 2020

  1. cpu/stm32: Fix gpio_init() / gpio_int_af() 

    - Do not set an intermediate mode, prepare correct mode settings in a temporary
  variable
- Consistently enabled the GPIO periph in gpio_init_af()
    - Previously, STM32 F1 did not require a separate call to gpio_init() prior
      to a call of gpio_init_af(), but other STM32 families did
    - Now, gpio_init_af() can be used without gpio_init() consistently
- STM32 F1: Do not touch ODR for non input pins
    - For input pins, this enables / disabled pull up resistors. For outputs,
      this register should remain untouched (according to API doc)
    @maribu
    maribu committed Jul 15, 2020
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  2. cpu/stm32: Fix uart_init() 

    - 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
    @maribu
    maribu committed Jul 15, 2020
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