void ssd1306_data(uint8_t c)
{
    if (use_i2c) {
        static uint8_t control = 0x40;
        I2C_TransferSeq_TypeDef seq;
        seq.addr = (0x3C << 1);
        seq.flags = I2C_FLAG_WRITE_WRITE;

        seq.buf[0].data = &control;
        seq.buf[0].len = 1;
        seq.buf[1].data = &c;
        seq.buf[1].len = 1;

        /* Do a polled transfer */
        I2C_Status = I2C_TransferInit(I2C0, &seq);

        while (I2C_Status == i2cTransferInProgress) {
            I2C_Status = I2C_Transfer(I2C0);
        }
        UNUSED_VARIABLE(I2C_Status);
    }
}