Date: Sat, 02 Sep 2000 17:51:49 -0600 From: Allen Campbell <allenc@verinet.com> To: Ian Smith <smithi@nimnet.asn.au> Cc: freebsd-stable@FreeBSD.ORG Subject: Re: bad 16550A maybe? Message-ID: <39B19295.3D66E41@verinet.com> References: <Pine.BSF.3.96.1000902074531.8872A-100000@gaia.nimnet.asn.au>
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Ian Smith wrote: > > On Fri, 1 Sep 2000, Warner Losh wrote: > > > In message <200009010501.WAA54972@tao.thought.org> Gary Kline writes: > > : This just showed up on my console (and dmesg) from my new 4.1 system: > > : sio0: 1 more silo overflow (total 1) > > : Could this be why moused is having trouble with recognizing my > > : COM1 mouse? Bad 16550A? > > > > Maybe. silo overflows happen because the machine is too slow to > > service the interrupt before the buffer overflows (but unless it is a > > 386SX25 you should have enough CPU power). It can also be caused by > > baud rate mismatches, but that's fairly rare and unusual (you usually > > get framing errors from a 16550A in this case). This can also be > > caused by other hardware misbehaving and blocking interrupts. > > Regarding later messages on this also: > > I ran a 386SX16 under DOS 5 / DESQView (~10 tasks in 6Mb) using David > Nugent's BNU FOSSIL driver as a Fidonet mailer/BBS for almost 9 years, > hardly ever seeing 16550A overflows at 14 byte thresholds, albeit 14.4k. > > Unless a slower FreeBSD system is running with extraordinarily high > interrupt latencies, it seems to me that setting a _default_ 8 byte > threshold would do little more than nearly double sio interrupt > frequency needlessly - even on a 386SX25! A knob, ok, sure ,, > > Cheers, Ian > You actually run a 386SX25? I have a 486/133 that has always experienced intense SILO overflows (yes, it is a true 16550, bought specifically to address this,) under FreeBSD. I suspect the problem is exasperated by PIO mode IDE and an ISA NE2000. Anyhow, the threshold most definitely MUST be lowered when communicating at >50Kbps with my USR modem. I would kill for a kernel option that makes patching unnecessary but the attitude, as expressed above, that anything faster than a 386SX25 can not possibly be too slow seems to preclude this. I believe there is a shortage of under powered hardware among the developers. Maybe that is a good thing. :) As evidenced by this thread where multiple respondents have pointed out similar experiences, the default threshold is too high for some hardware. This is despite the fact that the maintainers all seem to be convinced that it can't possibly be. A simple "knob" to get from FIFO_RX_HIGH to FIFO_RX_MEDH without patching would be very useful. -- Allen Campbell | Lurking at the bottom of the allenc@verinet.com | gravity well, getting old. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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