spi-loopback

SPI master TX + RX loopback. Demonstrates the open / transfer / close pattern from <alp/peripheral.h>. Wire MOSI to MISO on the carrier and run.

Source: examples/spi-loopback/.

board.yaml

schema_version: 2

som:
  sku: E1M-AEN701

carrier:
  name: E1M-EVK

cores:
  m55_hp:
    os: zephyr
    app: ./src
    peripherals: [spi]

diagnostics:
  log_level: info

Source (abbreviated)

#include <alp/peripheral.h>
#include <alp/e1m_pinout.h>

int main(void) {
    alp_spi_t *spi = alp_spi_open(&(alp_spi_config_t){
        .bus_id        = E1M_SPI0,
        .freq_hz       = 1000000u,
        .mode          = ALP_SPI_MODE_0,
        .bits_per_word = 8,
        .cs_pin_id     = E1M_GPIO_IO5,
    });
    if (spi == NULL) return -1;

    uint8_t tx[4] = { 0xAA, 0x55, 0xC3, 0x3C };
    uint8_t rx[4] = { 0 };
    alp_spi_transfer(spi, tx, rx, sizeof(tx));

    for (size_t i = 0; i < sizeof(tx); i++) {
        printk("[spi] tx=0x%02x  rx=0x%02x  %s\n",
               tx[i], rx[i], tx[i] == rx[i] ? "OK" : "MISMATCH");
    }

    alp_spi_close(spi);
    return 0;
}

Hardware

Short MOSI to MISO with a jumper. The chip-select line toggles around the transfer; the rest of the transaction reads back what was sent.

See also

• <alp/peripheral.h> reference — SPI
• Examples overview