usbserial: pl2303 tx xon/xoff flow control
Quoted 5 lines · Florian Zumbiehl
Before I investigated how to implement this patch I just saw that s/w flow control "didn't work", but my assumption was that that was due to buffering latencies, not because the kernel just ignored the request. But then, chances are a software implementation indeed wouldn't work very well anyway for exactly that reason?!
Indeed, the deep queues might prevent a software implementation from being very useful.
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The line discipline implementation kicks in whenever IXON is set, and can be used as a fallback for devices where automatic hardware and software flow control cannot be enabled concurrently in hardware for example.
Well, yeah, my guess would be that to actually make it work (well), one would need more than that? Like, implement rate control in software to keep the hardware buffers empty in order to achieve short reaction times? Which one would probably want to disable though when it's not needed in order to take advantage of the buffers?
Maybe, but chances are none of this is worth the added complexity. If you need XON/XOFF you should get a device which supports it in hardware.
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While non-hardware assisted usb serial XON/XOFF is currently broken in that transmission would not be halted, the line discipline would still swallow any escape characters.
Actually, that is required even for the pl2303, as it does not swallow the control characters itself.
Yeah, I noticed that too.
Thanks,
Johan
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