# SPI

HAL struct `SPI_HandleTypeDef*` used for handling SPI info.

For transmit/receive data use `spi_xfer` function:

```C
bool spi_xfer(
    SPI_HandleTypeDef* spi,
    uint8_t* tx_data, uint8_t* rx_data, size_t len,
    PubSubCallback cb, void* ctx);
```

* `tx_data` and `rx_data` size must be equal (and equal `len`)
* `cb` called after spi operation is completed, `(NULL, ctx)` passed to callback.

Blocking verison:

```C
inline static bool spi_xfer_block(SPI_HandleTypeDef* spi, uint8_t* tx_data, uint8_t* rx_data, size_t len) {
    semaphoreInfo s;
    osSemaphore block = createSemaphoreStatic(s);
    if(!spi_xfer(spi, tx_data, rx_data, len, RELEASE_SEMAPHORE, (void*)block)) {
        osReleaseSemaphore(block);
        return false;
    }
    osWaitSemaphore(block);
    return false;
}
```

## SPI Bus

Common implementation of SPI bus: serial interface + CS pin

```C
typedef struct {
    GpioPin* cs; ///< CS pin
    ValueMutex* spi; ///< <SPI_HandleTypeDef*>
} SpiBus;
```

## SPI device

For dedicated work with one device there is `SpiDevice` entity. It contains ValueMutex around SpiBus: after you acquire device you can acquire spi to work with it (don't forget SPI bus is shared around many device, release it after every transaction as quick as possible).

```C
typedef struct {
    ValueMutex* bus; ///< <SpiBus*>
} SpiDevice;
```

## SPI IRQ device

Many devices (like CC1101 and NFC) present as SPI bus and IRQ line. For work with it there is special entity `SpiIrqDevice`. Use `subscribe_pubsub` for subscribinq to irq events.

```C
typedef struct {
    ValueMutex* bus; ///< <SpiBus*>
    PubSub* irq;
} SpiIrqDevice;
```

## Display device

Special implementation of SPI bus: serial interface + CS, Res, D/I lines.

```C
typedef struct {
    GpioPin* cs; ///< CS pin
    GpioPin* res; ///< reset pin
    GpioPin* di; ///< D/I pin
    ValueMutex* spi; ///< <SPI_HandleTypeDef*>
} DisplayBus;

```C
typedef struct {
    ValueMutex* bus; ///< <DisplayBus*>
} DisplayDevice;
```

# SPI devices (F2)

* `/dev/sdcard` - SD card SPI, `SpiDevice`
* `/dev/cc1101_bus` - Sub-GHz radio (CC1101), `SpiIrqDevice`
* `/dev/nfc` - NFC (ST25R3916), `SpiIrqDevice`
* `/dev/display` - `DisplayDevice`
* `/dev/spiext` - External SPI (warning! Lock PA4, PA5, PA6, PA7)

### Application example

```C
// Be careful, this function called from IRQ context
void handle_irq(void* _arg, void* _ctx) {
}

void cc1101_example() {
    SpiIrqDevice* cc1101_device = open_input("/dev/cc1101_bus");
    if(cc1101_device == NULL) return; // bus not available, critical error

    subscribe_pubsub(cc1101_device->irq, handle_irq, NULL);

    {
        // acquire device as device bus
        SpiBus* spi_bus = acquire_mutex(cc1101_device->bus, 0);
        if(spi_bus == NULL) {
            printf("Device busy\n");
            // wait for device
            spi_bus = acquire_mutex_block(cc1101_device->bus);
        }
        
        // make transaction
        uint8_t request[4] = {0xDE, 0xAD, 0xBE, 0xEF};
        uint8_t response[4];

        {
            SPI_HandleTypeDef* spi = acquire_mutex_block(spi_bus->spi);

            gpio_write(spi_bus->cs, false);
            spi_xfer_block(spi, request, response, 4);
            gpio_write(spi_bus->cs, true);

            release_mutex(cc1101_device->spi, spi);
        }

        // release device (device bus)
        release_mutex(cc1101_device->bus, spi_bus);
    }
}
```