How to change UART and its pins for REPL in Pico?

[msawicki-poland]

I built Micropython with #define MICROPY_HW_ENABLE_UART_REPL (1) and uploaded uf2 file and it works
but how to change UART0 to UART1 and pins 0/1 to 4/5 for REPL in Pico, what I have to configure in Micropython project's files before building?

[zakharovvu]

maybe this will help on page 9 - https://www.waveshare.com/w/upload/b/b0/Pico_python_sdk.pdf

[msawicki-poland]

Unfortunately on page 9 there is nothing which can solve the problem.

[shariltumin]

To use UART0 pins other than the default ones, you can try to add these to your board's "mpconfigboard.h" file (for example):

#define MICROPY_HW_UART0_TX  (28)
#define MICROPY_HW_UART0_RX  (29)
#define MICROPY_HW_UART0_CTS (-1)
#define MICROPY_HW_UART0_RTS (-1)

GPIOs have specific functions as described in "rp2_af.csv" for UART0 we have these GPIOs to choose from:

$ grep UART0 *
rp2_af.csv:GPIO0,SPI0_RX,UART0_TX,I2C0_SDA,PWM0_A,SIO,PIO0,PIO1,,USB_OVCUR_DET
rp2_af.csv:GPIO1,SPI0_CS,UART0_RX,I2C0_SCL,PWM0_B,SIO,PIO0,PIO1,,USB_VBUS_DET
rp2_af.csv:GPIO2,SPI0_SCK,UART0_CTS,I2C1_SDA,PWM1_A,SIO,PIO0,PIO1,,USB_VBUS_EN
rp2_af.csv:GPIO3,SPI0_TX,UART0_RTS,I2C1_SCL,PWM1_B,SIO,PIO0,PIO1,,USB_OVCUR_DET
rp2_af.csv:GPIO12,SPI1_RX,UART0_TX,I2C0_SDA,PWM6_A,SIO,PIO0,PIO1,,USB_OVCUR_DET
rp2_af.csv:GPIO13,SPI1_CS,UART0_RX,I2C0_SCL,PWM6_B,SIO,PIO0,PIO1,,USB_VBUS_DET
rp2_af.csv:GPIO14,SPI1_SCK,UART0_CTS,I2C1_SDA,PWM7_A,SIO,PIO0,PIO1,,USB_VBUS_EN
rp2_af.csv:GPIO15,SPI1_TX,UART0_RTS,I2C1_SCL,PWM7_B,SIO,PIO0,PIO1,,USB_OVCUR_DET
rp2_af.csv:GPIO16,SPI0_RX,UART0_TX,I2C0_SDA,PWM0_A,SIO,PIO0,PIO1,,USB_VBUS_DET
rp2_af.csv:GPIO17,SPI0_CS,UART0_RX,I2C0_SCL,PWM0_B,SIO,PIO0,PIO1,,USB_VBUS_EN
rp2_af.csv:GPIO18,SPI0_SCK,UART0_CTS,I2C1_SDA,PWM1_A,SIO,PIO0,PIO1,,USB_OVCUR_DET
rp2_af.csv:GPIO19,SPI0_TX,UART0_RTS,I2C1_SCL,PWM1_B,SIO,PIO0,PIO1,,USB_VBUS_DET
rp2_af.csv:GPIO28,SPI1_RX,UART0_TX,I2C0_SDA,PWM6_A,SIO,PIO0,PIO1,,USB_VBUS_DET
rp2_af.csv:GPIO29,SPI1_CS,UART0_RX,I2C0_SCL,PWM6_B,SIO,PIO0,PIO1,,USB_VBUS_EN

MicroPython's REPL is hardcoded to use UART0. I dont know how to force it to use UART1 in the firmware. However, you can use os.dupterm() to connect the REPL to UART1 in the "boot.py".

[msawicki-poland]

So why on page 9 Pico Python SDK in table 1 we can find info about UART1 and pins 4 and 5 and caption "Default UART settings in MicroPython".

[shariltumin]

These are the default UART0 and UART1 pins. These default pins are defined in "machine_uart.c". By defining "MICROPY_HW_UART0_TX" other than the defaults, you can use other "legal" UART0 pins.

The note on page 10 says:

"This initially occupies the UART0 peripheral on RP-series microcontrollers. The UART1 peripheral is free for you to use in your Python code as a second UART."

Which I think means that REPL uses UART0 and you are free to use UART1.