[Rxtx] noob trouble with rxtx, losing bytes somewhere
Steffen.DETTMER at ingenico.com
Mon Dec 14 11:49:29 MST 2009
* M.Dec-Gazeta wrote on Mon, Dec 14, 2009 at 13:25 +0100:
> The kind of solution is a big size of the OS buffer, which will not
> overflows when Java is busy.
> But there is a lot of another things as well - vendors drivers, USB /RS232
> hardware and buffers there, USB1.1 vs USB 2.0 etc, another devices in the
> same USB hub etc.
Yes, and different unknown buffer sizes and drivers not telling
whether they overflowed also can be a pain...
> From my experience with real time systems (small embedded
> systems as well), the best way is to prepare serial (or another
> incoming) buffer as big as possible and thinking about tuning
> rest of the application - to have a time to empty this buffer
> in the meantime.
Yes, and I think this also is a good way for non-RT systems: let
the OS handle the "single bytes" and let the own application read
block-wise. If a read(byte) call takes 10 ms, only 10k would be
possible, but with a read(byte) or event based block readers
larger blocks are returned when the application calls less
frequently; well, but IIRC rxtx also implements some buffer.
> Few months ago I have helped my friend, who had to change their old
> soft/hard system on RS232 from UART16550 to USB/RS232 dongle.
> Timing in this system is very important.
Yeah, and it can create issues with latency, which under some
circumstances are be seriously bigger than with UART. Well, and
many different USB chips/drivers with their specifics... hum...
> We will have a lot to do when standards UARTS will gone !!!!! :)
Yes, I'm afraid you're right :)
interestingly half of those problems seem to come from ancient
UART limitations coming to USB just when emulating it :)
[AFAIK USB block transfer itself is reliable, fast and
relatively easy to use]
Yes, we won't get bored :)
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