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'serial' Driver

This driver powers the Split Keyboard feature.

?> Serial in this context should be read as sending information one bit at a time, rather than implementing UART/USART/RS485/RS232 standards.

Drivers in this category have the following characteristics:

bit bang and USART Half-duplex provide data and signaling over a single conductor
USART Full-duplex provide data and signaling over two conductors
They are all limited to single master and single slave communication scheme

Supported Driver Types

	AVR	ARM
bit bang	✔️	✔️
USART Half-duplex		✔️
USART Full-duplex		✔️

Driver configuration

Bitbang

Default driver, the absence of configuration assumes this driver. To configure it, add this to your rules.mk:

SERIAL_DRIVER = bitbang

Configure the driver via your config.h:

#define SOFT_SERIAL_PIN D0  // or D1, D2, D3, E6
#define SELECT_SOFT_SERIAL_SPEED 1 // or 0, 2, 3, 4, 5
                                   //  0: about 189kbps (Experimental only)
                                   //  1: about 137kbps (default)
                                   //  2: about 75kbps
                                   //  3: about 39kbps
                                   //  4: about 26kbps
                                   //  5: about 20kbps

ARM

!> The bitbang driver causes connection issues with bitbang WS2812 driver

Along with the generic options above, you must also turn on the PAL_USE_CALLBACKS feature in your halconf.h.

USART Half-duplex

Targeting STM32 boards where communication is offloaded to a USART hardware device. The advantage over bitbang is that this provides fast and accurate timings. SERIAL_PIN_TX for this driver is the configured USART TX pin. As this Pin is configured in open-drain mode an external pull-up resistor is needed to keep the line high (resistor values of 1.5k to 8.2k are known to work). To configure it, add this to your rules.mk:

SERIAL_DRIVER = usart

Configure the hardware via your config.h:

#define SOFT_SERIAL_PIN B6         // USART TX pin
//#define USART1_REMAP             // Remap USART TX and RX pins on STM32F103 MCUs, see table below.
#define SELECT_SOFT_SERIAL_SPEED 1 // or 0, 2, 3, 4, 5
                                   //  0: about 460800 baud
                                   //  1: about 230400 baud (default)
                                   //  2: about 115200 baud
                                   //  3: about 57600 baud
                                   //  4: about 38400 baud
                                   //  5: about 19200 baud
#define SERIAL_USART_DRIVER SD1    // USART driver of TX pin. default: SD1
#define SERIAL_USART_TX_PAL_MODE 7 // Pin "alternate function", see the respective datasheet for the appropriate values for your MCU. default: 7
#define SERIAL_USART_TIMEOUT 20    // USART driver timeout. default 20

You must also enable the ChibiOS SERIAL feature:

In your board's halconf.h: #define HAL_USE_SERIAL TRUE
In your board's mcuconf.h: #define STM32_SERIAL_USE_USARTn TRUE (where 'n' matches the peripheral number of your selected USART on the MCU)

Do note that the configuration required is for the SERIAL peripheral, not the UART peripheral.

USART Full-duplex

Targeting STM32 boards where communication is offloaded to a USART hardware device. The advantage over bitbang is that this provides fast and accurate timings. USART Full-Duplex requires two conductors without pull-up resistors instead of one conductor with a pull-up resistor unlike the Half-duplex driver. Due to its internal design it is more efficent, which can result in even faster transmission speeds.

Pin configuration

SERIAL_USART_TX_PIN is the USART TX pin, SERIAL_USART_RX_PIN is the USART RX pin. No external pull-up resistors are needed as the TX pin operates in push-pull mode. To use this driver the usart peripherals TX and RX pins must be configured with the correct Alternate-functions. If you are using a Proton-C everything is already setup, same is true for STM32F103 MCUs. For MCUs which are using a modern flexible GPIO configuration you have to specify these by setting SERIAL_USART_TX_PAL_MODE and SERIAL_USART_RX_PAL_MODE. Refeer to the corresponding datasheets of your MCU or find those settings in the table below.

Connecting the halves and Pin Swap

Please note that TX of the master half has to be connected with the RX pin of the slave half and RX of the master half has to be connected with the TX pin of the slave half! Usually this pin swap has to be done outside of the MCU e.g. with cables or on the pcb. Some MCUs like the STM32F303 used on the Proton-C allow this pin swap directly inside the MCU, this feature can be enabled using #define SERIAL_USART_PIN_SWAP in your config.h.

Setup

To use the driver, add this to your rules.mk:

SERIAL_DRIVER = usart

Next configure the hardware via your config.h:

#define SERIAL_USART_FULL_DUPLEX   // Enable full duplex operation mode.
#define SERIAL_USART_TX_PIN B6     // USART TX pin
#define SERIAL_USART_RX_PIN B7     // USART RX pin
//#define USART1_REMAP             // Remap USART TX and RX pins on STM32F103 MCUs, see table below.
//#define SERIAL_USART_PIN_SWAP    // Swap TX and RX pins if keyboard is master halve.
                                   // Check if this feature is necessary with your keyboard design and available on the mcu.
#define SELECT_SOFT_SERIAL_SPEED 1 // or 0, 2, 3, 4, 5
                                   //  0: 460800 baud
                                   //  1: 230400 baud (default)
                                   //  2: 115200 baud
                                   //  3: 57600 baud
                                   //  4: 38400 baud
                                   //  5: 19200 baud
#define SERIAL_USART_DRIVER SD1    // USART driver of TX and RX pin. default: SD1
#define SERIAL_USART_TX_PAL_MODE 7 // Pin "alternate function", see the respective datasheet for the appropriate values for your MCU. default: 7
#define SERIAL_USART_RX_PAL_MODE 7 // Pin "alternate function", see the respective datasheet for the appropriate values for your MCU. default: 7
#define SERIAL_USART_TIMEOUT 20    // USART driver timeout. default 20

You must also enable the ChibiOS SERIAL feature:

In your board's halconf.h: #define HAL_USE_SERIAL TRUE
In your board's mcuconf.h: #define STM32_SERIAL_USE_USARTn TRUE (where 'n' matches the peripheral number of your selected USART on the MCU)

Do note that the configuration required is for the SERIAL peripheral, not the UART peripheral.

Pins for USART Peripherals with Alternate Functions for selected STM32 MCUs

STM32F303 / Proton-C Datasheet

Pin Swap available: ✔️

Pin	Function	Mode
USART1
PA9	TX	AF7
PA10	RX	AF7
PB6	TX	AF7
PB7	RX	AF7
PC4	TX	AF7
PC5	RX	AF7
PE0	TX	AF7
PE1	RX	AF7
USART2
PA2	TX	AF7
PA3	RX	AF7
PA14	TX	AF7
PA15	RX	AF7
PB3	TX	AF7
PB4	RX	AF7
PD5	TX	AF7
PD6	RX	AF7
USART3
PB10	TX	AF7
PB11	RX	AF7
PC10	TX	AF7
PC11	RX	AF7
PD8	TX	AF7
PD9	RX	AF7

STM32F072 Datasheet