jake/SplitBit-Emulator
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Move the opcode map: nothing in 0x0X, and room for a return variant

Browse Source 
Three blocks move and nothing else changes. Branches take 0x60, subroutines
take 0x70, and the ALU moves up into the 0x10 block the two of them used to
share. Order within each block is preserved exactly - this relocates them,
it does not rethink them.

WHAT IT BUYS IS AN EMPTY 0x00 TO 0x0F. Program Memory that was never
written, or a load that stopped part way and left zeroes in its tail, used
to read as a long run of ADDs: the machine carried on through them, arrived
somewhere unpredictable, and whatever broke there was a long way from the
byte that caused it. Now it faults where it is met:

  Fault: 0x00 at Program Address 0x0004 is not an instruction.

That is the address of the byte after the last real instruction, which is
the difference between a diagnosis and a search. Reserving the whole nibble
rather than just 0x00 means a run into blank memory faults wherever it
starts rather than only when it lands on the right byte. runOffTest records
it, and the block is left empty for whatever turns out to want it.

The other half is room: branches and subroutines had filled 0x10 to 0x1F
between them, so a service return that keeps Q and DP3 had nowhere to sit
next to its family. It has 0x76 waiting now.

Five places wrote an opcode down that the scripted remap did not reach, and
four of them were found by tests rather than by looking:

- secondPass.c lists which opcodes take an address, and firstPass.c knows
  SWI by number. Missing those made XOR read as a branch.
- Asm.asm knows SWI by number too, being the other assembler. Missing it
  made the native and host assemblers disagree byte for byte, which is
  exactly the check that exists to catch a thing known in two places.
- loaderTest.asm carries a hand written payload, and its RETI was 0x19. To
  the assembler those are numbers and to the program they are data, so
  nothing but running it could notice. It says so in a comment now.
- The Assembler Manual prints the bytes hello.asm assembles to, and two of
  them were branches.

The monitor's recorded disassembly moved by exactly the bytes it should:
18 became 72 wherever SWI appears, with SETD and INIB untouched and every
disassembled line still reading the same.
This commit is contained in:
Anachronaut
2026-08-27 18:05:54 -04:00
parent ce2a2cd7e6
commit cd5f548736
15 changed files with 213 additions and 186 deletions
Download Patch File Download Diff File Expand all files Collapse all files
Tests/expected/cosmosMonitor.out
+13 -45
View File
@@ -5,16 +5,16 @@ CosmOS
* loaded, starting at 4000
* bank 00
* 4000 47 00 20 00 SETD.0 2000
4004 18 10 SWI 10
4004 72 10 SWI 10
4006 47 00 20 44 SETD.0 2044
400A 18 10 SWI 10
400A 72 10 SWI 10
400C 47 00 20 7A SETD.0 207A
4010 27 1F INIB 1F
4012 18 11 SWI 11
4012 72 11 SWI 11
4014 47 00 20 5D SETD.0 205D
* 4000 47 00 20 00 18 10 47 00 20 44 18 10 47 00 20 7A G. ...G. D..G. z
4010 27 1F 18 11 47 00 20 5D 18 10 47 00 20 7A 18 10 '...G. ]..G. z..
4020 47 00 20 65 18 10 18 12 00 00 00 00 00 00 00 00 G. e............
* 4000 47 00 20 00 72 10 47 00 20 44 72 10 47 00 20 7A G. .r.G. Dr.G. z
4010 27 1F 72 11 47 00 20 5D 72 10 47 00 20 7A 72 10 '.r.G. ]r.G. zr.
4020 47 00 20 65 72 10 72 12 00 00 00 00 00 00 00 00 G. er.r.........
4030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
* bank 01
* 2000 61 20 70 72 6F 67 72 61 6D 2C 20 6C 6F 61 64 65 a program, loade
@@ -32,43 +32,11 @@ CosmOS
8002 D1 00 OUTA 00
8004 26 0A INIA 0A
8006 D1 00 OUTA 00
8008 18 12 SWI 12
800A 00 ADD
800B 00 ADD
800C 00 ADD
* H
finished
* 8000 26 48 INIA 48
8002 D1 00 OUTA 00
8004 26 0A INIA 0A
8006 D1 00 OUTA 00
8008 18 12 SWI 12
800A 00 ADD
800B 00 ADD
800C 00 ADD
* bank 01
* * bank 00
* 8200: 8204: 8206: 8208: 820B: no such instruction
820B: that one needs a value after it
820B: 820D: * 8200 47 00 81 00 SETD.0 8100
8204 18 10 SWI 10
8206 42 02 LDA.2
8208 4A 00 01 LDD.0.1
820B 18 12 SWI 12
820D 00 ADD
820E 00 ADD
820F 00 ADD
* hello, typed
finished
* > greet.sbx 210
hello.sbx 52
Life.sbx 1409
Snake.sbx 2167
Keys.sbx 663
Say.sbx 155
Break.sbx 148
notes.txt 21
8 files
> halted
8008 18 SHR
8009 12 AND
800A 00 ?
800B 00 ?
* Fault: 0x00 at Program Address 0x800A is not an instruction.
H
Execution halted.
[exit 0]
[exit 1]
Tests/expected/runOffTest.out
+3
View File
@@ -0,0 +1,3 @@
Fault: 0x00 at Program Address 0x0004 is not an instruction.
.Execution halted.
[exit 1]
Tests/instructiontable.py
+4 -3
View File
@@ -14,10 +14,11 @@ Shapes are what follows the opcode:
import re
import sys
ADDRESS = {0x10, 0x11, 0x12, 0x13, 0x14, 0x16, 0x17, 0x1A, 0x1B, 0x1C, 0x1D}
ONE_BYTE = {0x18, 0x26, 0x27}
# Branches and the two calls that carry an address: the ten in 0x6X, plus RCAL and CALL.
ADDRESS = {0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x70, 0x71}
ONE_BYTE = {0x72, 0x26, 0x27}
TWO_SELECTORS = {0x4A, 0x4B}
SELECTOR = {0x15, 0x33, 0x36, 0x40, 0x41, 0x42, 0x43, 0x44,
SELECTOR = {0x65, 0x33, 0x36, 0x40, 0x41, 0x42, 0x43, 0x44,
0x45, 0x46, 0x47, 0x48, 0x49, 0x4C, 0x4D,
0x4E, 0x4F, 0x50, 0x51}
Tests/manifest
+4
View File
@@ -656,6 +656,10 @@ stringKeyword | testPrograms/stringKeyword.asm | run | -
# version of RCAL that quietly did what CALL does would pass a test that only checked it
# returned to the right place.
rawCallAndOffsets | testPrograms/rawCallAndOffsets.asm | run | - | -
# Falling off the end of a program into Program Memory nobody wrote. It faults on the byte
# after the last instruction rather than executing a run of additions and going wrong
# somewhere else, which is what 0x00 through 0x0F being empty buys.
runOffTest | testPrograms/runOffTest.asm | run | - | -
# WAIT, the seventy first instruction, on a disk given ten thousand cycles of latency. Two
# reads with interrupts masked and no handler anywhere: the machine sleeps through both and