STM32 MCO OUTPUT

[roland_vs]

The STM32's have a possibility to bring out a clock signal called `MCO`. It takes one of the selected clock sources, puts it through a divider and brings it out to a GPIO pin. I use it to spare a crystal in a design. Be aware that when having a long wire attached to the pin, you create a nice transmitter, but if ever need the MCO this is a way to add it to micropython:

Add to the `mpconfigboard.h` of your board:

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#define MICROPY_BOARD_EARLY_INIT    STM32F091RC_board_early_init
void STM32F091RC_board_early_init(void);

#define MICROPY_HW_MCO              (1)

Create or modify the `board_init.c` and place in your target board directory like `boards/NUCLEO_F091RC`

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#include STM32_HAL_H
#include "mpconfigboard.h"

void STM32F091RC_board_early_init(void) {
#if defined(MICROPY_HW_MCO)
/* redirect to:       source RCC_MCOSource:       prescaler RCC_MCODiv:
 * RCC_MCO1: PA8      RCC_MCO1SOURCE_HSI          RCC_MCODIV_1
 * RCC_MCO2: PC9      RCC_MCO1SOURCE_LSE          RCC_MCODIV_2
 *                    RCC_MCO1SOURCE_HSE          RCC_MCODIV_3
 *                    RCC_MCO1SOURCE_PLLCLK       RCC_MCODIV_4
 *                    RCC_MCO2SOURCE_SYSCLK       RCC_MCODIV_5
 *                    RCC_MCO2SOURCE_PLLI2SCLK
 *                    RCC_MCO2SOURCE_I2SCLK
 *                    RCC_MCO2SOURCE_HSE
 *                    RCC_MCO2SOURCE_PLLCLK
**/

    // output 8MHz to the PA8 output
    HAL_RCC_MCOConfig(RCC_MCO1, RCC_MCO1SOURCE_HSI, RCC_MCODIV_1);
#endif
}