Method read_from_serial_port

src/utils/libftdi_serial.cpp:171–196

}

int LibFTDISerial::read_from_serial_port (void *bytes_to_read, int size)
{
    // the ftdi will send us data after its latency (max 255ms, default
    // 16ms) times out, even if its buffer is empty, despite the usb
    // timeout.  libftdi does not enforce waiting for the usb timeout if
    // the chip responds, even if the chip responds with an empty buffer.
    // so, the read is repeated until the timeout is reached.

    // this latency behavior is documented in
    // http://www.ftdichip.com/Support/Documents/AppNotes/AN232B-04_DataLatencyFlow.pdf

    auto deadline =
        std::chrono::steady_clock::now () + std::chrono::milliseconds (ftdi.usb_read_timeout);
    last_result = 0;
    while (last_result == 0 && size > 0 && std::chrono::steady_clock::now () < deadline)
    {
        last_result = ftdi_read_data (&ftdi, static_cast<unsigned char *> (bytes_to_read), size);
        // TODO: negative values are libusb error codes, -666 means usb device unavailable
        if (last_result < 0)
        {
            log_error ("read_from_serial_port");
        }
    }

    return last_result;
}

int LibFTDISerial::send_to_serial_port (const void *message, int length)
{