mirror of
https://github.com/qmk/qmk_firmware
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91 lines
3.3 KiB
Markdown
91 lines
3.3 KiB
Markdown
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# UART Driver
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The UART drivers used in QMK have a set of common functions to allow portability between MCUs.
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Currently, this driver does not support enabling hardware flow control (the `RTS` and `CTS` pins) if available, but may do so in future.
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## AVR Configuration
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No special setup is required - just connect the `RX` and `TX` pins of your UART device to the opposite pins on the MCU:
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|MCU |`TX`|`RX`|`CTS`|`RTS`|
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|-------------|----|----|-----|-----|
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|ATmega16/32U2|`D3`|`D2`|`D7` |`D6` |
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|ATmega16/32U4|`D3`|`D2`|`D5` |`B7` |
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|AT90USB64/128|`D3`|`D2`|*n/a*|*n/a*|
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|ATmega32A |`D1`|`D0`|*n/a*|*n/a*|
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|ATmega328/P |`D1`|`D0`|*n/a*|*n/a*|
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## ChibiOS/ARM Configuration
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You'll need to determine which pins can be used for UART -- as an example, STM32 parts generally have multiple UART peripherals, labeled USART1, USART2, USART3 etc.
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To enable UART, modify your board's `halconf.h` to enable the serial driver:
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```c
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#define HAL_USE_SERIAL TRUE
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```
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Then, modify your board's `mcuconf.h` to enable the peripheral you've chosen, for example:
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```c
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#undef STM32_SERIAL_USE_USART2
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#define STM32_SERIAL_USE_USART2 TRUE
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```
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Configuration-wise, you'll need to set up the peripheral as per your MCU's datasheet -- the defaults match the pins for a Proton-C, i.e. STM32F303.
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|`config.h` override |Description |Default Value|
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|--------------------------|---------------------------------------------------------------|-------------|
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|`#define SERIAL_DRIVER` |USART peripheral to use - USART1 -> `SD1`, USART2 -> `SD2` etc.|`SD1` |
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|`#define SD1_TX_PIN` |The pin to use for TX |`A9` |
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|`#define SD1_TX_PAL_MODE` |The alternate function mode for TX |`7` |
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|`#define SD1_RX_PIN` |The pin to use for RX |`A10` |
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|`#define SD1_RX_PAL_MODE` |The alternate function mode for RX |`7` |
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|`#define SD1_CTS_PIN` |The pin to use for CTS |`A11` |
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|`#define SD1_CTS_PAL_MODE`|The alternate function mode for CTS |`7` |
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|`#define SD1_RTS_PIN` |The pin to use for RTS |`A12` |
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|`#define SD1_RTS_PAL_MODE`|The alternate function mode for RTS |`7` |
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## Functions
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### `void uart_init(uint32_t baud)`
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Initialize the UART driver. This function must be called only once, before any of the below functions can be called.
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#### Arguments
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- `uint32_t baud`
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The baud rate to transmit and receive at. This may depend on the device you are communicating with. Common values are 1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200.
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---
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### `void uart_putchar(uint8_t c)`
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Transmit a single byte.
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#### Arguments
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- `uint8_t c`
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The byte (character) to send, from 0 to 255.
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---
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### `uint8_t uart_getchar(void)`
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Receive a single byte.
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#### Return Value
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The byte read from the receive buffer.
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---
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### `bool uart_available(void)`
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Return whether the receive buffer contains data. Call this function to determine if `uart_getchar()` will return meaningful data.
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#### Return Value
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`true` if the receive buffer length is non-zero.
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