[Rxtx] RXTX and FTDI chips
Kustaa.Nyholm at planmeca.com
Thu Mar 11 23:42:19 MST 2010
> What your looking for is FT_GetLatencyTimer / FT_SetLatencyTimer, 0 - 255
> Quote : d2xx progamming pdf :
> "In the FT8U232AM and FT8U245AM devices, the receive buffer timeout that is
> used to flush
> remaining data from the receive buffer was fixed at 16 ms. In all other FTDI
> devices, this timeout is
> programmable and can be set at 1 ms intervals between 2ms and 255 ms. This
> allows the device
> to be better optimized for protocols requiring faster response times from
> short data packets."
thanks for posting, this is very interesting information, it appears that
the FTDI support engineer that I talked to was probably right, ie my
dongle has a chip where the flush timeout is fixed.
Good to know that there are devices where you can set the timeout,
although 2 ms can still degrade a protocol performance at high baudrates,
on the other hand, I suppose that a non-high speed USB serial port dongle
has an inherent limitation on how fast you can do a send/receive round trip
because of the inherent 1 ms polling period.
Using FT_SetLatencyTimer requires the use of JNA/JNI which has
some cross platform and installation/packaging implications where as
opening a serial port with Javacomm/RXTX, almost just works out of
I'm not sure if to be able to use FT_SetLatencyTimer needs the FTDI
drivers (I suppose so), whereas I would expect the some dongles
(maybe not the FTDI?) to work with the built in drivers of the OS?
All good information, thanks for sharing.
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