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SubjectRe: serial.c (race?)
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kees wrote:
>
> BTW: should it be possible to downgrade the port with setserial?
> I tried to use setserial to set uart to 16450 on a real 16550A
> but then nothing worked...

Yes, it should be possible. However Linux-2.2.x has a bug that it uses
the OLD FIFO depth instead of the new one. I submitted a patch for
that.

The transmit routine is kind of brain-dead. It waits for the FIFO to
drain completely, and then shoves complete FIFO depth of data into the
transmitter. This means that when the system has an IRQ latency larger
than a byte transmit time, (I.e. when you actually need the input
FIFO), then you will generate gaps in the output stream.

Stuffing 16 bytes into a 1 byte 16450 FIFO doesn't work. If the port
is set as a 16450, the FIFO won't be enabled, and the chip will discard
bytes that come in after the 1-byte-fifo fills up.

The workaround should be to use setserial to set the device to a 8250
(or 16550, without the A)) and then change it to 16450.

Then the "old" FIFO depth will also be "1".

Roger.

--
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2137555 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
------ Microsoft SELLS you Windows, Linux GIVES you the whole house ------


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