Hello,
If the event character is enabled and it is detected in the data stream, then the contents of the devices buffer is sent immediately. The event character is not stripped out of the data stream by the device or by the drivers, it is up to the application to remove it. Event characters may be turned on and off depending on whether large amounts of random data or small command sequences are to be sent. The event character will not work if it is the first character in the buffer. It needs to be the second or higher. The reason for this being applications that use the Internet for example, will program the event character as '$7E'. All the data is then sent and received in packets that have '$7E' at the start and at the end of the packet. In order to maximise throughput and to avoid a packet with only the starting '$7E' in it, the event character does not trigger on the first position.
You may also want to take a look at the latency timer.
The latency timer is a form of time-out mechanism for the read buffer of FTDI devices. When a FT_Read instruction is sent to the device, data will not be sent back to the host PC until the requested number of bytes has been read. If the requested number of bytes never comes, the device would not send data back.
The latency timer counts from the last time data was sent back to the PC. If the latency timer expires, the device will send what data it has available to the PC regardless of how many bytes it is waiting on. The latency timer will then reset and begin counting again.
The default value for the latency timer is 16ms. This value may be customised by adding or changing the following entries in the FTDIPORT.INF file of the driver before installation.
[FtdiPort232.NT.HW.AddReg]
HKR,,"LatencyTimer",0x00010001,50
This example will set the default latency timer value to 50ms. The valid range for the latency timer is 1ms - 255ms, although 1ms is not recommended as this is the same as the USB frame length.
The latency timer value is held in the registry under:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\FTDIBUS\{Device VID, PID and serial number}\0000\Device Parameters\LatencyTimer
Please see
AN232B-04 Data Throughput, Latency and Handshaking for additional information on the latency timer.
Best Regards,
FTDI Community
