The SPI Master drivers used in QMK have a set of common functions to allow portability between MCUs.
In most cases, the SPI Master driver code is automatically included if you are using a feature or driver which requires it, such as OLED.
However, if you need to use the driver standalone, add the following to your rules.mk:
SPI_DRIVER_REQUIRED = yesYou can then call the SPI API by including spi_master.h in your code.
No special setup is required - just connect the SS, SCK, MOSI and MISO pins of your SPI devices to the matching pins on the MCU:
| MCU | SS | SCK | MOSI | MISO |
|---|---|---|---|---|
| ATmega16/32U2/4 | B0 | B1 | B2 | B3 |
| AT90USB64/128/162 | B0 | B1 | B2 | B3 |
| ATmega32A | B4 | B7 | B5 | B6 |
| ATmega328/P | B2 | B5 | B3 | B4 |
You may use more than one slave select pin, not just the SS pin. This is useful when you have multiple devices connected and need to communicate with them individually. SPI_SS_PIN can be passed to spi_start() to refer to SS.
You'll need to determine which pins can be used for SPI -- as an example, STM32 parts generally have multiple SPI peripherals, labeled SPI1, SPI2, SPI3 etc.
To enable SPI, modify your board's halconf.h to enable SPI:
#define HAL_USE_SPI TRUE\n#define SPI_USE_WAIT TRUE\n#define SPI_SELECT_MODE SPI_SELECT_MODE_PADThen, modify your board's mcuconf.h to enable the peripheral you've chosen, for example:
#undef STM32_SPI_USE_SPI2\n#define STM32_SPI_USE_SPI2 TRUEConfiguration-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.
config.h Override | Description | Default |
|---|---|---|
SPI_DRIVER | SPI peripheral to use - SPI1 -> SPID1, SPI2 -> SPID2 etc. | SPID2 |
SPI_SCK_PIN | The pin to use for SCK | B13 |
SPI_SCK_PAL_MODE | The alternate function mode for SCK | 5 |
SPI_MOSI_PIN | The pin to use for MOSI | B15 |
SPI_MOSI_PAL_MODE | The alternate function mode for MOSI | 5 |
SPI_MISO_PIN | The pin to use for MISO | B14 |
SPI_MISO_PAL_MODE | The alternate function mode for MISO | 5 |
As per the AVR configuration, you may choose any other standard GPIO as a slave select pin, which should be supplied to spi_start().
If a complete SPI interface is not required, then the following can be done to disable certain SPI pins, so they don't occupy a GPIO unnecessarily:
config.h: #define SPI_MISO_PIN NO_PINconfig.h: #define SPI_MOSI_PIN NO_PINmcuconf.h: #define SPI_SELECT_MODE SPI_SELECT_MODE_NONE, in this case the slavePin argument passed to spi_start() may be NO_PIN if the slave select pin is not used.void spi_init(void) Initialize the SPI driver. This function must be called only once, before any of the below functions can be called.
bool spi_start(pin_t slavePin, bool lsbFirst, uint8_t mode, uint16_t divisor) Start an SPI transaction.
pin_t slavePin
The QMK pin to assert as the slave select pin, eg. B4.
bool lsbFirst
Determines the endianness of the transmission. If true, the least significant bit of each byte is sent first.
uint8_t mode
The SPI mode to use:
| Mode | Clock Polarity | Clock Phase |
|---|---|---|
0 | Leading edge rising | Sample on leading edge |
1 | Leading edge rising | Sample on trailing edge |
2 | Leading edge falling | Sample on leading edge |
3 | Leading edge falling | Sample on trailing edge |
uint16_t divisor
The SPI clock divisor, will be rounded up to the nearest power of two. This number can be calculated by dividing the MCU's clock speed by the desired SPI clock speed. For example, an MCU running at 8 MHz wanting to talk to an SPI device at 4 MHz would set the divisor to 2.
false if the supplied parameters are invalid or the SPI peripheral is already in use, or true.
spi_status_t spi_write(uint8_t data) Write a byte to the selected SPI device.
uint8_t dataSPI_STATUS_TIMEOUT if the timeout period elapses, or SPI_STATUS_SUCCESS.
spi_status_t spi_read(void) Read a byte from the selected SPI device.
SPI_STATUS_TIMEOUT if the timeout period elapses, or the byte read from the device.
spi_status_t spi_transmit(const uint8_t *data, uint16_t length) Send multiple bytes to the selected SPI device.
const uint8_t *datauint16_t lengthdata.SPI_STATUS_TIMEOUT if the timeout period elapses, SPI_STATUS_ERROR if some other error occurs, otherwise SPI_STATUS_SUCCESS.
spi_status_t spi_receive(uint8_t *data, uint16_t length) Receive multiple bytes from the selected SPI device.
uint8_t *datauint16_t lengthdata.SPI_STATUS_TIMEOUT if the timeout period elapses, SPI_STATUS_ERROR if some other error occurs, otherwise SPI_STATUS_SUCCESS.
void spi_stop(void) End the current SPI transaction. This will deassert the slave select pin and reset the endianness, mode and divisor configured by spi_start().