On 30-Jul-18 11:45, Johnny Billquist wrote: > On 2018-07-30 15:51, Timothe Litt wrote: >> On 30-Jul-18 09:30, Paul Koning wrote: >>> Yes, that is the standard way to do this. I have never seen the >>> code you quoted before and I can't imagine any reason for doing that. >> A memory address test's verification pass. Check that memory >> contains address of self. Of course, you need a >> >> bne fail >> following the compare :-) > > Not to mention that it will succeed or fail depending on which PDP-11 > model you run the code on? :-) Oddly enough, we did have quality control, and it usually worked.
Diagnostics are often CPU-specific. This was fixed after the 11/20. I might have done this - it represents a 40% savings in instructions for the loop: ;11/20 safe Many other 11s Some other 11s 10$: movr3, r0 10$: cmp r3,(r3)+ 10$: cmp r3,(r3)+ cmp r0, (r3)+ bne fail bne fail bne fail sob r1, 10$ dec r1 dec r1 bne 10$ bne 10$ 20-40% reduction in instructions of an inner loop at boot time is worth a runtime check for the 11/20 - if I cared (e.g. a BIST is probably in processor-specific ROM, so no need to check).
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