Method do_transfer

libraries/AP_HAL_ChibiOS/SPIDevice.cpp:174–223

low level transfer function */

  low level transfer function
 */
bool SPIDevice::do_transfer(const uint8_t *send, uint8_t *recv, uint32_t len)
{
    bool old_cs_forced = cs_forced;

    if (!set_chip_select(true)) {
        return false;
    }

    bool ret = true;

#if defined(HAL_SPI_USE_POLLED)
    for (uint32_t i=0; i<len; i++) {
        const uint8_t b = spiPolledExchange(spi_devices[device_desc.bus].driver, send?send[i]:0);
        if (recv) {
            recv[i] = b;
        }
    }
#else
    if (!bus.bouncebuffer_setup(send, len, recv, len)) {
        set_chip_select(old_cs_forced);
        return false;
    }
    osalSysLock();
    hal.util->persistent_data.spi_count++;
    if (send == nullptr) {
        spiStartReceiveI(spi_devices[device_desc.bus].driver, len, recv);
    } else if (recv == nullptr) {
        spiStartSendI(spi_devices[device_desc.bus].driver, len, send);
    } else {
        spiStartExchangeI(spi_devices[device_desc.bus].driver, len, send, recv);
    }
    // we allow SPI transfers to take a maximum of 20ms plus 32us per
    // byte. This covers all use cases in ArduPilot. We don't ever
    // expect this timeout to trigger unless there is a severe MCU
    // error
    const uint32_t timeout_us = 20000U + len * 32U;
    msg_t msg = osalThreadSuspendTimeoutS(&spi_devices[device_desc.bus].driver->thread, TIME_US2I(timeout_us));
    osalSysUnlock();
    if (msg == MSG_TIMEOUT) {
        ret = false;
        if (!hal.scheduler->in_expected_delay()) {
            INTERNAL_ERROR(AP_InternalError::error_t::spi_fail);
        }
        spiAbort(spi_devices[device_desc.bus].driver);
    }
    bus.bouncebuffer_finish(send, recv, len);
#endif
    set_chip_select(old_cs_forced);
    return ret;
}

/*
  this pulses the clock for n bytes. The data is ignored.