keychron_qmk_firmware/docs/platformdev_rp2040.md

Raspberry Pi RP2040

The following table shows the current driver status for peripherals on RP2040 MCUs:

System	Support
ADC driver	Support planned (no ETA)
Audio	✔️
Backlight	✔️
I2C driver	✔️
SPI driver	✔️
WS2812 driver	✔️ using PIO driver
External EEPROMs	✔️ using I2C or SPI driver
EEPROM emulation	✔️
serial driver	✔️ using SIO or PIO driver
UART driver	Support planned (no ETA)

GPIO

!> The GPIO pins of the RP2040 are not 5V tolerant!

Pin nomenclature

To address individual pins on the RP2040, QMK uses the GPx abbreviation -- where the x stands for the GPIO number of the pin. This number can likely be found on the official pinout diagram of your board. Note that these GPIO numbers match the RP2040 MCU datasheet, and don't necessarily match the number you see printed on the board. For instance the Raspberry Pi Pico uses numbers from 1 to 40 for their pins, but these are not identical to the RP2040's GPIO numbers. So if you want to use the pin 11 of the Pico for your keyboard, you would refer to it as GP8 in the config files.

Alternate functions

The RP2040 features flexible GPIO function multiplexing, this means that every pin can be connected to nearly all the internal peripherals like I2C, SPI, UART or PWM. This allows for flexible PCB designs that are much less restricted in the selection of GPIO pins. To find out which pin can use which peripheral refer to the official Raspberry PI RP2040 datasheet section 1.4.3 GPIO functions.

Selecting hardware peripherals and drivers

QMK RP2040 support builds upon ChibiOS and thus follows their convention for activating drivers and associated hardware peripherals. These tables only give a quick overview which values have to be used, please refer to the ChibiOS specific sections on the driver pages.

I2C Driver

RP2040 Peripheral	mcuconf.h values	I2C_DRIVER
I2C0	RP_I2C_USE_I2C0	I2CD0
I2C1	RP_I2C_USE_I2C1	I2CD1

To configure the I2C driver please read the ChibiOS/ARM section.

SPI Driver

RP2040 Peripheral	mcuconf.h values	SPI_DRIVER
SPI0	RP_SPI_USE_SPI0	SPID0
SPI1	RP_SPI_USE_SPI1	SPID1

To configure the SPI driver please read the ChibiOS/ARM section.

Double-tap reset boot-loader entry :id=double-tap

The double-tap reset mechanism is an alternate way in QMK to enter the embedded mass storage UF2 boot-loader of the RP2040. It enables bootloader entry by a fast double-tap of the reset pin on start up, which is similar to the behavior of AVR Pro Micros. This feature activated by default for the Pro Micro RP2040 board, but has to be configured for other boards. To activate it, add the following options to your keyboards config.h file:

#define RP2040_BOOTLOADER_DOUBLE_TAP_RESET // Activates the double-tap behavior
#define RP2040_BOOTLOADER_DOUBLE_TAP_RESET_TIMEOUT 200U // Timeout window in ms in which the double tap can occur.
#define RP2040_BOOTLOADER_DOUBLE_TAP_RESET_LED GP17 // Specify a optional status led by GPIO number which blinks when entering the bootloader

Pre-defined RP2040 boards

QMK defines two boards that you can choose from to base your RP2040 powered keyboard upon. These boards provide pre-configured default pins and drivers.

Generic Pro Micro RP2040

This is the default board that is chosen, unless any other RP2040 board is selected in your keyboards rules.mk file. It assumes a pin layout for the I2C, SPI and Serial drivers which is identical to the Sparkfun Pro Micro RP2040, however all values can be overwritten by defining them in your keyboards config.h file. The double-tap reset to enter boot-loader behavior is activated by default.

Driver configuration define	Value
I2C driver
I2C_DRIVER	I2CD1
I2C1_SDA_PIN	GP2
I2C1_SCL_PIN	GP3
SPI driver
SPI_DRIVER	SPID0
SPI_SCK_PIN	GP18
SPI_MISO_PIN	GP20
SPI_MOSI_PIN	GP19
Serial driver
SERIAL_USART_DRIVER (SIO Driver only)	SIOD0
SOFT_SERIAL_PIN	undefined, use SERIAL_USART_TX_PIN
SERIAL_USART_TX_PIN	GP0
SERIAL_USART_RX_PIN	GP1

?> The pin-outs of Adafruit's KB2040 and Boardsource's Blok both deviate from the Sparkfun Pro Micro RP2040. Lookup the pin-out of these boards and adjust your keyboards pin definition accordingly if you want to use these boards.

Generic RP2040 board

This board can be chosen as a base for RP2040 keyboards which configure all necessary pins and drivers themselves and do not wish to leverage the configuration matching the Generic Pro Micro RP2040 board. Thus it doesn't provide any pre-configured pins or drivers. To select this board add the following line to your keyboards rules.mk file.

BOARD = GENERIC_RP_RP2040

Split keyboard support

Split keyboards are fully supported using the serial driver in both full-duplex and half-duplex configurations. Two driver subsystems are supported by the RP2040, the hardware UART based SIO and the Programmable IO based PIO driver.

Feature	SIO Driver	PIO Driver
Half-Duplex operation		✔️
Full-Duplex operation	✔️	✔️
TX and RX pin swapping		✔️
Any GPIO as TX and RX pin	Only UART capable pins	✔️
Simple configuration		✔️

The PIO driver is much more flexible then the SIO driver, the only "downside" is the usage of PIO resources which in turn are not available for advanced user programs. Under normal circumstances, this resource allocation will be a non-issue.

RP2040 second stage bootloader selection

As the RP2040 does not have any internal flash memory it depends on an external SPI flash memory chip to store and execute instructions from. To successfully interact with a wide variety of these chips a second stage bootloader that is compatible with the chosen external flash memory has to be supplied with each firmware image. By default an W25Q080 compatible bootloader is assumed, but others can be chosen by adding one of the defines listed in the table below to your keyboards config.h file.

Compatible with flash chip	Selection
W25Q080	Selected by default
AT25SF128A	#define RP2040_FLASH_AT25SF128A
GD25Q64CS	#define RP2040_FLASH_GD25Q64CS
W25X10CL	#define RP2040_FLASH_W25X10CL
IS25LP080	#define RP2040_FLASH_IS25LP080
Generic 03H flash	#define RP2040_FLASH_GENERIC_03H