How to add UART9 support to the firmware for VCC_GND_H743VI?

[daleka]

Hi,
I am building a custom MicroPython firmware for the VCC_GND_H743VI board and want to enable UART9 support.

I added the following lines to mpconfigboard.h:
#define MICROPY_HW_UART9_TX (pin_E12)
#define MICROPY_HW_UART9_RX (pin_E13)

However, when compiling, I get the following error:
uart.c:534:21: error: 'UART9' undeclared (first use in this function)

Question:
What else needs to be done to enable UART9 without errors?
Do I need to modify mpconfigboard.mk, uart.c, or stm32h7xx_hal_conf.h?