Adding as many UARTs as possible to NUCLEO_F746ZG

[mdaeron]

Looking into the board definition for NUCLEO_F746ZG, I see the following:

// UART config
#define MICROPY_HW_UART2_TX         (pin_D5)
#define MICROPY_HW_UART2_RX         (pin_D6)
#define MICROPY_HW_UART2_RTS        (pin_D4)
#define MICROPY_HW_UART2_CTS        (pin_D3)
#define MICROPY_HW_UART3_TX         (pin_D8)
#define MICROPY_HW_UART3_RX         (pin_D9)
#define MICROPY_HW_UART6_TX         (pin_G14)
#define MICROPY_HW_UART6_RX         (pin_G9)
#define MICROPY_HW_UART_REPL        PYB_UART_3
#define MICROPY_HW_UART_REPL_BAUD   115200

Accordingly, in the REPL I can only define machine.UART(2), machine.UART(3) and machine.UART(6).

I would like to add as many hardware UARTs as possible to the firmware.

Question 1: Should I just add lines such as below?

#define MICROPY_HW_UART1_TX         (pin_??)
#define MICROPY_HW_UART1_RX         (pin_??)
#define MICROPY_HW_UART4_TX         (pin_??)
#define MICROPY_HW_UART4_RX         (pin_??)
#define MICROPY_HW_UART5_TX         (pin_??)
#define MICROPY_HW_UART5_RX         (pin_??)

Question 2: How do I choose which pins to assign to the new UARTs? Should I go through the specs and identify pins that are compatible with each new UART and not already used?

Question 3: How many UARTS can I add in this way? Should I go through the specs to find out how many UART devices exist? How do I know which ones are already reserved for something? If I understand correctly, UART3 is exclusively reserved for the REPL? Are there any other reserved devices?

[jkorte-dev]

you can have a look at https://github.com/micropython/micropython/blob/master/ports/stm32/boards/stm32f746_af.csv
where all pin capabilities are listed.