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The Tuesday 2007-04-10 at 13:12 +0200, Roger Oberholtzer wrote:
> Perhaps this is related to an issue I am starting to look in to. I have
> a system with a number of PCI I/O cards (firewire, video, SCSI, network)
> as well as the good old serial ports (16550-based - not PCI). In some
> system loads (not excessive) I see that the serial port driver starts to
> report data overruns. I also see missing characters in GPS data read
> over the serial port at this time.
Surprising... :-O
> I am trying to see why these overruns
> are happening. The serial port is operating at 38400. The 16550 can only
> buffer 16 characters in hardware. So the device driver must service the
> hardware within that time or data will be lost (handshake issues aside -
> eventually some buffer can get full).
Hum.
This should not happen. The hardware should be able to signal the other
side that it is not ready to receive data - that's what hardware handshake
is for. Even an old 8086 was able to service the serial port at maximum
speed, and if it couldn't, the other end would pause. The same should
happen now with modern hardware.
I would look at the hardware handshake lines first.
> Could it be that some device
> driver has a higher priority and is blocking the serial port driver from
> servicing the hardware? I am running whatever default priorities are in
> SUSE 10.0. Am I looking in the right direction?.
Maybe.
Interrupts are interrupts, should be attended regardless of conditions,
although maybe later. If there is an unwanted delay, and there can be
unless you have on a real time system (warrantied maximum response time),
the system (hardware) should be able to inform the sending side to slow
down and wait.
If hardware handshaking is impossible, revert to software handshake (much
slower, chars have to be sent back)
- --
Cheers,
Carlos E. R.
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