Re: 11/40 misbehaviour

From: Rich Alderson (news_at_alderson.users.panix.com)
Date: 08/11/04

  • Next message: RHB: "Re: 11/40 misbehaviour" 
    Date: 10 Aug 2004 20:43:41 -0400

    John Santos <JOHN@egh.com> writes:

    > Are you sure it is a PSW bit 4 (T bit, indicates trace trap), and not a
    > trap through the vector at 4? <snip>

    Yes, I was quite sure. I was, however, confusing two occurrences. Error code
    TBT is "T-bit trap"--and I did get it on the other box, quite often.

    > Trap through 4 could be anything... T4 is Timeout and other errors,
    > according to my PDP 11/40 Processor Handbook. A Unibus timeout could
    > be caused by incorrect device configuration, but I think the device
    > setup code at boot time should try to protect you against this. (It
    > does on RSTS, by disabling non-existent devices, but I'm not nearly
    > as familiar with RSX.) Memory could be going out to lunch, and failing
    > to respond to reads or writes. Or the bus cable(s), jumper(s) or
    > terminators could be bad, and randomly changing an address bit causing
    > a memory or device address to be wrong.

    Error code T04 is precisely this, bus timeouts or odd-address word references.

    > Have you tried all the standard things, i.e. reseating boards, checking
    > PS voltages, etc.?

    Yes.

    > If that doesn't help, try paring down the system to the minimal
    > working configuration (CPU, console terminal, enough memory to run,
    > and the system disk) and then add things back one at a time until
    > the problem recurs.

    This is a minimal system: 28KW memory, console, RH11, RX01.

    > I haven't seen PDP-11/40 diags in years. We used to have a tape
    > (9-track, 800 bpi) of them, but it is long gone.

    Just on general principles, and not my own need, that's too bad. 

    -- 
Rich Alderson                                       | /"\ ASCII ribbon     |
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