Add template STDIO retargeting via CMSIS-Driver UART

[ReinhardKeil]

Add a template that uses CMSIS-Driver UART with 'select="STDOUT UART Template"'

Effectively this code (but with configurable driver instance)

#include "retarget_stdout.h"
#include "Driver_USART.h"

#include <stdint.h>

extern ARM_DRIVER_USART Driver_USART0;

static ARM_DRIVER_USART * const stdout_usart = &Driver_USART0;
static uint8_t stdout_usart_initialized;

#ifndef STDOUT_USART_BAUDRATE
#define STDOUT_USART_BAUDRATE 115200U
#endif

static int stdout_usart_ensure_initialized (void) {
  int32_t status;

  if (stdout_usart_initialized != 0U) {
    return 0;
  }

  status = stdout_usart->Initialize(NULL);
  if (status != ARM_DRIVER_OK) {
    return -1;
  }

  status = stdout_usart->PowerControl(ARM_POWER_FULL);
  if (status != ARM_DRIVER_OK) {
    return -1;
  }

  status = stdout_usart->Control(
    ARM_USART_MODE_ASYNCHRONOUS |
    ARM_USART_DATA_BITS_8       |
    ARM_USART_PARITY_NONE       |
    ARM_USART_STOP_BITS_1       |
    ARM_USART_FLOW_CONTROL_NONE,
    STDOUT_USART_BAUDRATE
  );
  if (status != ARM_DRIVER_OK) {
    return -1;
  }

  status = stdout_usart->Control(ARM_USART_CONTROL_TX, 1U);
  if (status != ARM_DRIVER_OK) {
    return -1;
  }

  stdout_usart_initialized = 1U;
  return 0;
}

/**
  Put a character to the stdout

  \param[in]   ch  Character to output
  \return          The character written, or -1 on write error.
*/
int stdout_putchar (int ch) {
  uint8_t c;

  if (stdout_usart_ensure_initialized() != 0) {
    return -1;
  }

  /* If caller prints bare '\n', emit CRLF on the wire. */
  if ((uint8_t)ch == (uint8_t)'\n') {
    (void)stdout_putchar('\r');
  }

  /* Serialize by waiting for any previous send to complete. */
  while (stdout_usart->GetStatus().tx_busy != 0U) {
  }

  c = (uint8_t)ch;
  if (stdout_usart->Send(&c, 1U) != ARM_DRIVER_OK) {
    return -1;
  }

  while (stdout_usart->GetStatus().tx_busy != 0U) {
  }

  return ch;
}

[VladimirUmek]

This was addressed by adding STDOUT:UART&CMSIS component (also for STDIN, STDERR). See the relevant PR #74.