Kinetis SPI driver. More...

Kinetis SPI driver.

The SPI baud rate and other timings are generated from the bus clock via prescalers, the hardware module allows for very detailed timing configuration, but a tool exists to generate a standard timing configuration for any given module clock frequency. The timing configuration tool is found in cpu/kinetis/dist/calc_spi_scalers

Finer tuning of timings than the RIOT SPI API is capable of is supported by modifying the generated configuration. See the reference manual for your Kinetis CPU (Chapter: "SPI module, Functional description, Module baud rate and clock delay generation") for a description of each delay.

The SPI driver supports using GPIO pins for chip select, as an alternative to using hardware chip select. The pins specified in spi_config[x].pin_cs[y] are the hardware chip select pins, designated SPIx_PCSy in the hardware reference documentation. These pins can not be chosen arbitrarily but must be selected from the pins which support the SPIx_PCSy function in the pin multiplexing table found in the reference manual.

To use a hardware controlled chip select pin, use the SPI_HWCS macro instead of GPIO_PIN when calling spi_acquire() in the device driver. Software managed CS signals can use any GPIO pin, at the cost of extra delays in the transfer because of the additional overhead of calling gpio_set/clear at every transfer.

SPI configuration example (for periph_conf.h):

static const uint32_t spi_clk_config[] = {
- Use cpu/kinetis/dist/calc_spi_scalers to generate the timing configuration -
};

static const spi_conf_t spi_config[] = {
    {
        .dev      = SPI0,
        .pin_miso = GPIO_PIN(PORT_D, 3),
        .pin_mosi = GPIO_PIN(PORT_D, 2),
        .pin_clk  = GPIO_PIN(PORT_D, 1),
        .pin_cs   = {
            GPIO_PIN(PORT_D, 0),
            GPIO_PIN(PORT_D, 4),
            GPIO_PIN(PORT_D, 5),
            GPIO_PIN(PORT_D, 6),
            GPIO_UNDEF
        },
        .pcr      = GPIO_AF_2,
        .simmask  = SIM_SCGC6_SPI0_MASK
    },
    {
        .dev      = SPI1,
        .pin_miso = GPIO_PIN(PORT_E, 3),
        .pin_mosi = GPIO_PIN(PORT_E, 1),
        .pin_clk  = GPIO_PIN(PORT_E, 2),
        .pin_cs   = {
            GPIO_PIN(PORT_E, 4),
            GPIO_UNDEF,
            GPIO_UNDEF,
            GPIO_UNDEF,
            GPIO_UNDEF
        },
        .pcr      = GPIO_AF_2,
        .simmask  = SIM_SCGC6_SPI1_MASK
    }
};
#define SPI_NUMOF           ARRAYSIZE(spi_config)