SPI RTIO loopback

Overview

This sample demonstrates how to perform SPI transfers using RTIO. It uses two SPI controllers, acting as SPI controller and peripheral/target respectively.

Requirements

This sample requires two SPI controllers, one supporting the SPI controller role, one supporting the SPI peripheral/target role, connected to the same SPI bus.

Note

Remember to connect the relevant SPI controllers to the bus physically.

Board support

Any board which meets the requirements must use an overlay to specify which SPI controller will act as the controller, and which as the peripheral/target. This is done using the devicetree by adding SPI device nodes to the relevant SPI controllers, adding the nodelabel spi_controller to the SPI device SPI controller acting as controller, and spi_target to the SPI device SPI controller acting as peripheral/target. These two SPI device nodes describe the same SPI device, from the perspective of the SPI controller and SPI peripheral/target respectively.

&spi22 {
        status = "okay";
        cs-gpios = <&gpio2 10 GPIO_ACTIVE_LOW>;

        spi_controller: spi-device@0 {
                   compatible = "vnd,spi-device";
                   reg = <0>;
                   spi-max-frequency = <DT_FREQ_M(8)>;
        };
};

&spi21 {
        status = "okay";

        spi_target: spi-device@0 {
                   compatible = "vnd,spi-device";
                   reg = <0>;
                   spi-max-frequency = <DT_FREQ_M(8)>;
        };
};

If necessary, add any board specific configs to the board specific conf fragment:

CONFIG_SPI_STM32_INTERRUPT=y

Transferred data sizes

One can tune the number of data bytes exchanged during the tests using the sample specific configuration options:

CONFIG_SAMPLE_DATA_WRITE_SIZE
CONFIG_SAMPLE_DATA_READ_SIZE
CONFIG_SAMPLE_SPI_MODE_0
CONFIG_SAMPLE_SPI_MODE_1
CONFIG_SAMPLE_SPI_MODE_2
CONFIG_SAMPLE_SPI_MODE_3
CONFIG_SAMPLE_SPI_BIT_ORDER_MSB
CONFIG_SAMPLE_SPI_BIT_ORDER_LSB