SPI.cpp

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/**
 * @file spi.cpp
 *
 * Base class for devices connected via SPI.
 *
 * @todo Work out if caching the mode/frequency would save any time.
 *
 * @todo A separate bus/device abstraction would allow for mixed interrupt-mode
 * and non-interrupt-mode clients to arbitrate for the bus.  As things stand,
 * a bus shared between clients of both kinds is vulnerable to races between
 * the two, where an interrupt-mode client will ignore the lock held by the
 * non-interrupt-mode client.
 */

#include "SPI.hpp"

#include <px4_platform_common/px4_config.h>
#include <nuttx/arch.h>

#ifndef CONFIG_SPI_EXCHANGE
# error This driver requires CONFIG_SPI_EXCHANGE
#endif

namespace device
{

SPI::SPI(const char *name, const char *devname, int bus, uint32_t device, enum spi_mode_e mode, uint32_t frequency) :
    CDev(name, devname),
    _device(device),
    _mode(mode),
    _frequency(frequency),
    _dev(nullptr)
{
    // fill in _device_id fields for a SPI device
    _device_id.devid_s.bus_type = DeviceBusType_SPI;
    _device_id.devid_s.bus = bus;
    _device_id.devid_s.address = (uint8_t)device;
    // devtype needs to be filled in by the driver
    _device_id.devid_s.devtype = 0;
}

SPI::~SPI()
{
    // XXX no way to let go of the bus...
}

int
SPI::init()
{
    /* attach to the spi bus */
    if (_dev == nullptr) {
        int bus = get_device_bus();

        if (!board_has_bus(BOARD_SPI_BUS, bus)) {
            return -ENOENT;
        }

        _dev = px4_spibus_initialize(bus);
    }

    if (_dev == nullptr) {
        DEVICE_DEBUG("failed to init SPI");
        return -ENOENT;
    }

    /* deselect device to ensure high to low transition of pin select */
    SPI_SELECT(_dev, _device, false);

    /* call the probe function to check whether the device is present */
    int ret = probe();

    if (ret != OK) {
        DEVICE_DEBUG("probe failed");
        return ret;
    }

    /* do base class init, which will create the device node, etc. */
    ret = CDev::init();

    if (ret != OK) {
        DEVICE_DEBUG("cdev init failed");
        return ret;
    }

    /* tell the workd where we are */
    DEVICE_LOG("on SPI bus %d at %d (%u KHz)", get_device_bus(), PX4_SPI_DEV_ID(_device), _frequency / 1000);

    return PX4_OK;
}

int
SPI::transfer(uint8_t *send, uint8_t *recv, unsigned len)
{
    int result;

    if ((send == nullptr) && (recv == nullptr)) {
        return -EINVAL;
    }

    LockMode mode = up_interrupt_context() ? LOCK_NONE : _locking_mode;

    /* lock the bus as required */
    switch (mode) {
    default:
    case LOCK_PREEMPTION: {
            irqstate_t state = px4_enter_critical_section();
            result = _transfer(send, recv, len);
            px4_leave_critical_section(state);
        }
        break;

    case LOCK_THREADS:
        SPI_LOCK(_dev, true);
        result = _transfer(send, recv, len);
        SPI_LOCK(_dev, false);
        break;

    case LOCK_NONE:
        result = _transfer(send, recv, len);
        break;
    }

    return result;
}

int
SPI::_transfer(uint8_t *send, uint8_t *recv, unsigned len)
{
    SPI_SETFREQUENCY(_dev, _frequency);
    SPI_SETMODE(_dev, _mode);
    SPI_SETBITS(_dev, 8);
    SPI_SELECT(_dev, _device, true);

    /* do the transfer */
    SPI_EXCHANGE(_dev, send, recv, len);

    /* and clean up */
    SPI_SELECT(_dev, _device, false);

    return PX4_OK;
}

int
SPI::transferhword(uint16_t *send, uint16_t *recv, unsigned len)
{
    int result;

    if ((send == nullptr) && (recv == nullptr)) {
        return -EINVAL;
    }

    LockMode mode = up_interrupt_context() ? LOCK_NONE : _locking_mode;

    /* lock the bus as required */
    switch (mode) {
    default:
    case LOCK_PREEMPTION: {
            irqstate_t state = px4_enter_critical_section();
            result = _transferhword(send, recv, len);
            px4_leave_critical_section(state);
        }
        break;

    case LOCK_THREADS:
        SPI_LOCK(_dev, true);
        result = _transferhword(send, recv, len);
        SPI_LOCK(_dev, false);
        break;

    case LOCK_NONE:
        result = _transferhword(send, recv, len);
        break;
    }

    return result;
}

int
SPI::_transferhword(uint16_t *send, uint16_t *recv, unsigned len)
{
    SPI_SETFREQUENCY(_dev, _frequency);
    SPI_SETMODE(_dev, _mode);
    SPI_SETBITS(_dev, 16);          /* 16 bit transfer */
    SPI_SELECT(_dev, _device, true);

    /* do the transfer */
    SPI_EXCHANGE(_dev, send, recv, len);

    /* and clean up */
    SPI_SELECT(_dev, _device, false);

    return PX4_OK;
}

} // namespace device