傳送字串

static int spi_write_bytes(struct spi_device *spi, unsigned char *txbuf, int txlen)
{
    int ret = 0;
    struct spi_message msg;
    struct spi_transfer xfer = {
        .len  = txlen,
        .tx_buf  = txbuf,
        .delay_usecs = 5,
        .bits_per_word = 8,
    };
    spi_message_init(&msg);
    spi_message_add_tail(&xfer, &msg);
    ret = spi_sync(spi, &msg);
    if
 
 (ret < 0)
        printk(KERN_ERR "spi send error\n");
}

傳送單個字元

static int spi_write_byte(struct spi_device *spi, unsigned char data)
{
    int ret = 0;
    char buf[1];
    struct spi_message msg;
    struct spi_transfer xfer = {
        .len  = 1,
        .tx_buf  = buf,
        .bits_per_word
 
 = 8,
    };
    buf[0] = data;
    spi_message_init(&msg);
    spi_message_add_tail(&xfer, &msg);
    ret = spi_sync(spi, &msg);
    if (ret < 0)
        printk(KERN_ERR "spi send error\n");
}

讀取函式

static int spi_read(struct spi_device *spi, unsigned char addr,\
        unsigned
 
 int length, unsigned char *data)
{
    int ret = 0;
    unsigned char buf[1];
    struct spi_message  msg;
    struct spi_transfer     xfer[] = { 
        {
            .tx_buf     = buf,
            .bits_per_word  = 8,
            .len        = sizeof(buf),
        },
        {
            .rx_buf     = data,
            .bits_per_word  = 8,
            .len        = length,
        }
    };  

    buf[0] = (addr | 0x80); 

    if (!spi || !data) {
        ret = -EINVAL;
        return ret;
    }   

    spi_message_init(&msg);

    spi_message_add_tail(&xfer[0], &msg);
    spi_message_add_tail(&xfer[1], &msg);

    return spi_sync(spi, &msg);
}