Messages in this thread | | | Subject | Re: serial.c (race?) | Date | Sat, 16 Oct 1999 09:18:38 +0200 (MEST) | From | (Rogier Wolff) |
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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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