11/34 failing trap test

Don North ak6dn at mindspring.com
Sun Aug 20 01:09:57 CDT 2006


Pete Turnbull wrote:
> On Aug 19 2006, 9:38, Wolfe, Julian wrote:
>
>> I got the 11/34 up and running, and I loaded XXDP. It fails the trap
>> test. The instructions state you should examine the stack pointer
>> (777706) which shows it to be a value of 000470. This is supposed to
>> tell you the address of the Program Counter, right? So I load address
>> 470, and the value is 000330. What instruction is failing? Am I
>> reading this right?
>
> Yes, the stack pointer points to the last address used on the stack,
> and that will be the value of the PC when it called the error
> subroutine, or to put it another way, the address of the next
> instruction to be executed had the JSR not been taken. It's failing at
> whatever test was just before location 330 -- which is surprisingly
> low. You'd need to look at the listing to see what the test was.
>
The trap test typically does a halt-on-failure, so at what address does
your CPU halt? After knowing the halt address (and the failed test) the
SP and what is on the stack may or may not be useful data.

BTW the listing of this diagnostic is online at:
http://www.bitsavers.org/pdf/dec/pdp11/xxdp/listings/AC-8045D-MC_CFKABD0-1134-Traps-Tst_Apr77.pdf
in case you already didn't know this.

If indeed the CPU did halt at 330 this is in the vector space which is
typically populated with .+2/halt word pairs (a 'trapcatcher' in DEC terms).

Don North





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