SUMMARY:many zs0: silo overflow messages

From: Loki Jorgenson (
Date: Fri Jun 14 1991 - 08:29:16 CDT

        Summary: Observing a "flood" of the well-known

                "zs0: silo overflow"

messages along with slowing machine, tty sessions missing key strokes,
etc. on a SUN3/50 running SUN OSv3.5.

        Thanks to: (Brent Chivers) (Dennis Morse) (Thomas Kilday)

        Everyone who every had a SUN3 knows this message. Causing
consternation and confusion, it is normally a harmless message. The
device "zs0" is a serial line driver; it controls the serial ports
on the motherboard. SUN Microsystems usually advises that you ignore
this message.

        However, in our case, we were seeing several dozen per minute.
This was just after I changed a couple of Ether buffer chips on the
machine. It turned out that our modems connected to the serial ports
were in a funny state because the RS232 connectors were making
intermittent contact; they were flooding the serial ports with garbage.
And, of course, the serial circuit was probably unbalanced due to bad

        Alternately, some other helpful users mentioned these potential
sources (apologies to a couple of others whose replies got trashed):

From: (Brent Chivers)

This suggests a lot of activity on one or more serial ports.
Do you have a modem attached that's echoing back login prompts?
Or an unhappy printer?

We often get this when we reboot. Various terminals have
been queueing up keystrokes on port servers, and when the
machines wake up again a lot of garbage comes flooding in
on the serial ports.

From: (Thomas Kilday)
        This error indicates a bad keyboard. Try replacing it
        and see if that fixes it.

From: (Dennis Morse)

The "zs0" is a Zilog 8530 SCC serial communications driver. See the man
page for zs(4s). This is most likely not a hardware problem by a kernel
configuration issue. It sounds like the kernel buffers are too small.
The easiest way to fix this is to increase the "maxusers" parameter in the
kernel config file "/sys/sun3/conf/<YOUR_CUSTOM_KERNEL_NAME>".

I sure hope you are already building custom kernels, since the 3/50 is so
slow and has such limited memory that it needs all the help it can get. We
typically set our "maxusers" parameter to 10-14 for our SPARCstation
clients, depending on the amount of RAM installed. When we had Sun 3/50s
we set "maxusers" to 6 or 8. The value of 4 in GENERIC_SMALL is too low.

                             _ _ _ _
Loki Jorgenson / / _ _ _ _ _ \ \ node: loki@Physics.McGill.CA
Grad/Systems Manager /_/_/_/_/ \_\_\_\_\ BITNET: PY29@MCGILLA
Physics, McGill University \ \ \_\_\_/_/_/ / / fax: (514) 398-3733
Montreal Quebec CANADA \_\_ _/_/ phone: (514) 398-7027

                      -* Anatomically correct *-

This archive was generated by hypermail 2.1.2 : Fri Sep 28 2001 - 23:06:15 CDT