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From: naddy@mips.inka.de (Christian Weisgerber)
Date: Sat, 4 Oct 2008 20:05:18 +0000 (UTC)
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Originator: naddy@mips.inka.de (Christian Weisgerber)
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Subject: Re: Jump in serial line latency?
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Ed Schouten <ed@80386.nl> wrote:

> > It looks like something has added a lot of latency to characters
> > coming in the serial port.  I have no idea when this happened.
> 
> Do you have time/interest to pinpoint the cause of the problem?

It looks like the problem crept in with the sio(4) to uart(4) switch.

More specifically, it's the Rx FIFO setting of the 16550 UART.
After adding 0x100 to hint.uart.0.flags and rebooting, I can confirm
that the ~800 ms offset is gone.

I seem to remember that sio(4) automatically set the FIFO threshold
to 1 for low bit rates.  uart(4) is not so clever.

-- 
Christian "naddy" Weisgerber                          naddy@mips.inka.de