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Jeff 2017-03-27 14:34:23 -07:00 • committed by Jeff Parsons
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_posts/2017-03-24-stepping-through-pdp-10-diagnostics.md
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@ -12,9 +12,10 @@ 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 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" %}
@ -91,8 +92,9 @@ Next, I tried [KA10 Basic Instruction Diagnostic #4 (MAINDEC-10-DAKAD-B-D)](/app
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 instruction should have
"skipped if equal." There was a bug in the [cpuops.js](/modules/pdp10/lib/cpuops.js) *CMP()* function:
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:
```javascript
/**
@ -116,7 +118,7 @@ And here's the correction:
return (dst < PDP10.INT_LIMIT? dst : dst - PDP10.WORD_LIMIT) - (src < PDP10.INT_LIMIT? src : src - PDP10.WORD_LIMIT);
```
Just a stupid typo. After fixing that and trying again, the diagnostic got a bit farther:
After fixing that and trying again, the diagnostic got a bit farther:
>> g
running
@ -139,8 +141,9 @@ Just a stupid typo. After fixing that and trying again, the diagnostic got a bi
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 AOBJN added 000001000001 to it, the result
should have been 000001000000, but because other another typo, this time in the *opAOBJN()* function:
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
because other another typo, this time in the *opAOBJN()* function:
```javascript
/**
@ -174,5 +177,8 @@ not WORD_MASK, to truncate the value to 36 bits. Here's the corrected line:
var dst = (this.readWord(acc) + 0o000001000001) % PDP10.WORD_LIMIT;
```
There are more PDPjs emulation failures in these [Basic Instruction Diagnostics](/apps/pdp10/diags/klad/) from DEC,
but I've run out of time today. To be continued....
*[@jeffpar](http://twitter.com/jeffpar)*
*Mar 24, 2017*