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Jeff 2017-03-27 19:18:05 -07:00 • committed by Jeff Parsons
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_posts/2017-03-24-stepping-through-pdp-10-diagnostics.md
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@ -12,10 +12,9 @@ machines:
---
Now that the PDPjs MACRO-10 Mini-Assembler is [limping along](/blog/2017/03/21/), it's time to start assembling some
of DEC's PDP-10 "Basic Instruction" diagnostics and loading them into a test machine.
The first diagnostic I tried was [KA10 Basic Instruction Diagnostic #1 (MAINDEC-10-DAKAA-B-D)](/apps/pdp10/diags/klad/dakaa/),
which has been loaded into the machine below.
of DEC's PDP-10 "Basic Instruction" diagnostics and loading them into a test machine. The first diagnostic I tried was
[KA10 Basic Instruction Diagnostic #1 (MAINDEC-10-DAKAA-B-D)](/apps/pdp10/diags/klad/dakaa/), which has been loaded into
the machine below.
{% include machine.html id="testka10" %}
@ -59,9 +58,17 @@ Happily, this was a good outcome, because 035057 is the end of the test. If you
035057 254 00 0 00 030057 ENDXX: JRST BEGEND ;LOOP PROGRAM
I had similar success with Basic Instruction Diagnostics #2 (MAINDEC-10-DAKAB-B-D) and #3 (MAINDEC-10-DAKAC-B-D).
I had similar success with [Diagnostic #2 (MAINDEC-10-DAKAB-B-D)](/apps/pdp10/diags/klad/dakab/).
However, when I tried [KA10 Basic Instruction Diagnostic #4 (MAINDEC-10-DAKAD-B-D)](/apps/pdp10/diags/klad/dakad/):
Problems started to crop up in [Diagnostic #3 (MAINDEC-10-DAKAC-B-D)](/apps/pdp10/diags/klad/dakac/):
CAME [0,-1] ;PASS TEST IF C(AC)=0,,-1
Based on the comment, it's clear what they really meant was either "[0,,-1]" or "[XWD 0,-1]". However, they still got the
desired result, which means that even when the assembler parses an mnemonic-less instruction like "0,-1", it must still truncate
the second (address) operand. Once I generated the appropriate value (000000,777777), the test passed.
And I had several failures running [Diagnostic #4 (MAINDEC-10-DAKAD-B-D)](/apps/pdp10/diags/klad/dakad/):
>> a 30724 /apps/pdp10/diags/klad/dakad/DAKAD.MAC
starting PCjs MACRO-10 Mini-Assembler...
@ -94,9 +101,10 @@ However, when I tried [KA10 Basic Instruction Diagnostic #4 (MAINDEC-10-DAKAD-B-
032005: 312140 034462 CAME 3,34462 ;history=2
032006: 254200 032007 HALT 32007 ;history=1
This looked less good. Both AC3 and memory location 34462 contained 400000000000, so the CAME ("Compare AC with Memory
and Skip if Equal") instruction should have "skipped" the HALT, but it didn't. Thus was due to a bug in the
[cpuops.js](/modules/pdp10/lib/cpuops.js) *CMP()* function:
In this case, both AC3 and memory location 34462 contained 400000000000, so the CAME ("Compare AC with Memory
and Skip if Equal") instruction should have "skipped" the HALT, but it didn't.
Thus was due to a bug in the [cpuops.js](/modules/pdp10/lib/cpuops.js) *CMP()* function:
```javascript
/**
@ -114,7 +122,7 @@ PDP10.CMP = function(dst, src)
};
```
And here's the correction:
Basically, there was a typo. Here's the correction:
```javascript
return (dst < PDP10.INT_LIMIT? dst : dst - PDP10.WORD_LIMIT) - (src < PDP10.INT_LIMIT? src : src - PDP10.WORD_LIMIT);
@ -143,8 +151,8 @@ After fixing that and trying again, the diagnostic got a bit farther:
033444: 312000 034574 CAME 0,34574 ;history=2
033445: 254200 033446 HALT 33446 ;history=1
The problem here was that after `SETO 0,0`, AC0 contained 777777777777, so when the AOBJN ("Add One to Both Halves
of AC and Jump if Negative") instruction added 000001000001 to it, the result should have been 000001000000, but
The problem here was that after `SETO 0,0`, AC0 contained 777777,777777, so when the AOBJN ("Add One to Both Halves
of AC and Jump if Negative") instruction added 000001,000001 to it, the result should have been 000001,000000, but
because other another typo, this time in the *opAOBJN()* function:
```javascript
@ -179,18 +187,9 @@ not WORD_MASK, to truncate the value to 36 bits. Here's the corrected line:
var dst = (this.readWord(acc) + 0o000001000001) % PDP10.WORD_LIMIT;
```
The next problem I encountered involved this instruction in DEC's "DAKAC" diagnostic:
CAME [0,-1] ;PASS TEST IF C(AC)=0,,-1
Based on the comment, it's clear what they really meant was either "[0,,-1]" or "[XWD 0,-1]". However, they still got the
desired result, which means that even when the assembler parses an mnemonic-less instruction like "0,-1", it must still truncate
the second (address) operand.
The last few problems I ran into during my initial testing were in DEC's "DAKAD" diagnostic. When it tests the `SOJ` and `SOS`
instructions, it expects the carry and overflow flags to be set consistently with an *addition* of negative 1 (777777,777777)
rather than a *subtraction* of positive 1. That was an easy fix, but I'm not convinced that all flag-related issues are resolved,
so more arithmetic operation testing will be performed at a later date.
The last few problems involved the `SOJ` and `SOS` instructions, which expected the carry and overflow flags to be set
consistently with an *addition* of negative 1 (777777,777777) rather than a *subtraction* of positive 1. That was an easy fix,
but I'm not convinced that all flag-related issues are resolved, so more arithmetic operation testing is required.
Finally, when the "DAKAD" diagnostic generated an indirect word reference: