Date: Sun, 03 Sep 2000 15:04:24 -0600 From: Allen Campbell <allenc@verinet.com> To: freebsd-stable@FreeBSD.ORG Subject: Re: bad 16550A maybe? Message-ID: <39B2BCD8.CCFF9655@verinet.com> References: <Pine.BSF.3.96.1000902074531.8872A-100000@gaia.nimnet.asn.au> <39B19295.3D66E41@verinet.com> <200009030158.TAA01926@nomad.yogotech.com>
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Nate Williams wrote:
>
> > > > 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.
> > >
> > > 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.
> >
> > 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.
>
> Which version of FreeBSD? I've been running (well, I quit the company,
> but the box is still up) a 486/66 with 4 16550A's running full-blast @
> 115K on the modems with nary a problem.
4.0-STABLE at the moment. The problem began somewhere in the 3.X
series. Prior to 3.X, I never saw a SILO overflow from this machine.
> The box is a firewall, DNS, email, and modem server for a small office,
> and is working great.
>
> The only modifications were to continually upgrade the software such as
> BIND and SENDMAIL where remote root exploits were possible, but
> otherwise it's a stock FreeBSD 2.2.8 system. (No X, of course.)
>
> > 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.
>
> We're running the same setup (PIO IDE and a NE2000), and I've ran all 4
> modems (2 USR Sportsters and 2 USR V.Everythings) full-blast one day to
> see how well it would handle it. Not once did it even hiccup or lose
> packets.
Try loading the IDE drive and the NE2000 at the same time. I don't see
SILO overflows while the box is simply driving the serial port, but let
some other host on my network make the NFS exported drives busy while
the modem is working and the SILO overflows erupt.
Nate, I don't know what to say to this except you only need to search
-questions or usenet to find countless examples of the same problem with
the same symptoms being reported. These people have no agenda other
than fixing the problem. Perhaps the PIC/chipset implementation makes
this less cut and dry and, in your case, you got lucky. Maybe it's the
early version of FreeBSD you are running. Sun spots perhaps? I don't
know.
> > 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'm with Rod Grimes in stating that something happened in later releases
> of FreeBSD that makes this difficult or impossible.
Huh?
Jim King posted the patch that does the trick earlier in this thread. I
know for fact this works. I've been applying something similar to sio.c
since 3.1-RELEASE. It basically makes a one line change that lowers the
16550A threshold to 8 bytes. How is it difficult or impossible to
accommodate this with an #ifdef based on a kernel option, i.e. option
16550_LOW_THRESHOLD... ?
And here it is again:
--- sio.c.orig Wed Aug 16 09:29:34 2000
+++ sio.c Fri Sep 1 14:53:47 2000
@@ -2345,7 +2345,7 @@
* latencies are larger.
*/
com->fifo_image = t->c_ospeed <= 4800
- ? FIFO_ENABLE : FIFO_ENABLE |
FIFO_RX_HIGH;
+ ? FIFO_ENABLE : FIFO_ENABLE |
FIFO_RX_MEDH;
#ifdef COM_ESP
/*
* The Hayes ESP card needs the fifo DMA mode bit set
--
Allen Campbell | Lurking at the bottom of the
allenc@verinet.com | gravity well, getting old.
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