Twenty four places moved Q into A or B by pushing it and popping it back.
That is four bus cycles and two bytes to do what MVQA does in one of each,
and several of them are inside loops - Life, the calculator, int8. Nineteen
more loaded zero with INIA 0d0 where RSTA says the same thing in one byte.
Both are equivalent at the CPU rather than by assertion: RSTA and INIA both
leave Status alone, and PSHQ followed by POPA nets to A = Q with the Stack
Pointer where it started. The one difference is that the pair leaves a copy
of Q in memory just below the Stack Pointer and MVQA does not, which
nothing here reads.
Five recorded outputs moved and every one of them says the change worked:
- 16x16Life fits five more generations into the same cycle budget, the
first 457 lines identical, because the loop got cheaper.
- Life.sbx is 1409 bytes rather than 1411, in three tests that list it.
- Edit.sbx is 1995 rather than 1996.
That last one broke a check I added this morning, and the hole is worth
recording: the CosmOS README's claim about Edit's size did not have the
word "Edit" on the same line as the number, because the subject was in the
sentence before, so the check that measures quoted sizes skipped it
silently. The sentence now names what it is talking about, which makes it
both checkable and clearer, and the check fails on a wrong number there.
Comments on either half of a replaced pair are carried onto the
instruction that replaces them, so nothing anybody wrote was lost.
SplitLint reports valid assembly that has a shorter direct expression:
zero loads that could be RSTA or RSTB, Q moved through the stack where MVQA
would do, self-cancelling push and pop pairs, assignments overwritten
before use, unreachable fallthrough, one-byte pointer moves that could be
INCD or DECD, a branch to the label directly below it, a SETD reloading an
address the pointer already holds, and branches whose carry is known.
Its model is deliberately local and conservative: every label and every
directive forgets all known state, so a claim only ever lives inside a
straight-line region. It knows the calling convention - CALL forgets DP3
and keeps the rest, RCAL and SWI forget everything - and it shares
assembly.o with the assembler, so an added opcode cannot leave it holding a
private copy of the instruction table.
260 warnings across the corpus, of which three were wrong in the way that
matters: branchTest.asm and interruptFlagTest.asm exist to check that a
branch whose carry is known behaves correctly, so a diagnostic saying the
outcome is known is exactly right and exactly unwanted.
A line whose comment says "splitlint: <reason>" is now not reported on. THE
REASON IS REQUIRED and a bare marker is refused, because a suppression
nobody explained outlives whatever made it necessary. Suppressed warnings
are not counted, so --fatal-warnings does not fail on one, and the number
of them is printed at the end so the claim is visible rather than silent.
Tests/lint.sh checked a TOTAL: twenty three warnings expected, twenty three
found. That number stays right while the thing behind it goes wrong - a
rule that stopped firing while another fired twice would pass, and so would
a rule reporting at the wrong line. It now checks which warning came out
and at which line, that nothing else came out, and that the four lines
meant to stay quiet did. Confirmed by breaking one rule's message and
watching it name that rule: the old assertion passed the same sabotage,
because the warning still fired and the count never moved.
Written with the user while I was away; my part is the suppression
mechanism, the harness rewrite, and the three marks in the test programs.
HALT is terminal - stepCPU returns at once when the Halt Flag is up, so a
halted machine does not execute, service devices, or take an interrupt -
and that has to stay true, because every test ends with a halt and "halted"
is how a program says it has finished. The consequence was that SplitBit
had no way to wait at all. Every wait was a spin, and a spin is bus
traffic: 11.5% of Type over a 14K file on a disk of ten thousand cycles,
after read-ahead had already hidden three quarters of the latency.
WAIT is 0xFE, one byte, no operands, sitting under HALT where the
instruction that almost stops the machine belongs. Three decisions in it:
- A line already standing means there is nothing to wait for, so WAIT does
nothing. That is what makes test-then-wait race-free.
- Any line ends the wait, masked or not, so a program can sleep on a device
it has no handler for and read its status afterwards. Masking says who
answers a request, not whether it happened.
- A line that wakes the CPU without being dispatched is taken down by the
WAIT. Left standing it would be found by the next WAIT, which would
return at once - the program would spin exactly as before while looking
as though it slept.
Waiting is NOT a Status bit, and that is the trap avoided rather than a
gap: Status rides into the interrupt frame and comes back out, so a machine
interrupted mid-wait would return from its handler still waiting, and wait
again for what it had already been given. An internal field instead.
Idle cycles are counted apart from bus cycles and the halt line says so
when there are any, which is what makes the difference observable at all -
with the line-clearing removed the total moves by ONE cycle, 20,100 against
20,099, and only the idle half changes, halving to 9,976. A test on
totals could never have seen it. Tests/terminal.sh asks that question,
being the file for things a recorded output cannot see, and fails with the
clear removed while "both reads finished" still passes.
Three collisions, all found by building it:
- 0xFE was the assembler's "not an instruction" sentinel. getOpcode now
answers a negative NOT_AN_OPCODE, which is outside the range of every
possible answer instead of inside the unused part of it.
- 0xFE was also what faultTest and faultResumeTest executed to provoke a
fault. They now use 0xFD and say why, because they did not fail when it
became an instruction - they HUNG, having started sleeping instead.
- Keys.asm has had a label called "wait" for a year, and mnemonics are
matched uppercased. What that reported was "Branch without label" at the
BRQ thirty lines away. The assembler now refuses a label that is already
an instruction, at the label, by name; every instruction added takes a
word out of the space of label names, so this will happen again.
The six settled back on the twenty fourth, built now.
RCAL and RRET are a call that puts nothing back. CALL restores A, B and Data
Pointers 0 through 2, which costs ten bytes of Stack and is why a subroutine
here can only hand anything back through Q, DP3 or memory. RCAL costs two and
restores nothing, which is what a short leaf routine wants and is unsafe in
exactly the way the name says.
They are a pair because the frames are different sizes: returning from one
through the other walks the Stack to somewhere that was never a return address.
That was the user's correction to the original proposal, which had a raw call
and no raw return.
DPUA and DPDA offset a Data Pointer by A; DPUW and DPDW by A and B together,
most significant first. DPUP and DPDN take a byte written into the program, so
moving a pointer by something just worked out meant storing it and loading it
back. Down as well as up on symmetry grounds, which was also the user's call -
the argument against it came from counting uses in a corpus written under the
constraint.
The opcodes sit where they belong: 0x16 and 0x1E immediately below CALL and RET,
and 0x4E through 0x51 at the end of the Data Pointer family. All six fit shapes
that already existed, so instructiontable.py needed only set membership and both
machine side copies of the table regenerated from it unchanged.
Checked at every level it exists at: the emulator runs them, the host assembler
encodes them, the monitor disassembles all six with the right lengths, and the
assembler that runs on the machine builds a program using them byte for byte
identically to the host - and that program runs.
The recorded test measures what the two calls COST as well as what they put
back, because an RCAL that quietly did what CALL does would still return to the
right place. It does not survive that: returned through RRET, it hangs.
docs.sh can read a two word number now. The count of instructions taking a Data
Pointer went past twenty, and the pattern only allowed one word, so the check
would have reported that the manual had stopped saying it rather than that the
number was wrong.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
DPUP takes an immediate, so an offset of one is legal and does exactly the
right thing. It is also three bytes where INCD is two, and reads as "offset
the pointer up by one" where INCD reads as "step the pointer".
56 of them across 15 files: the system, the assembler, the editor, and eight
test programs. CosmOS is 9,564 bytes to 9,537, the native assembler 11,648
to 11,635, and every program in the repository together 49 bytes lighter.
The worst offender was numbers.asm, written this week, where every sixteen
bit helper reaches the low byte and comes back the long way round. It is the
file every other part of the assembler includes, so it is the first thing
anybody reads when they go looking - and it was teaching them the long way.
Pattern matched off sbfs.asm rather than off the instruction table I had
just embedded in two programs.
THIS IS NOT TWO WAYS TO DO ONE THING. DPUP takes an arbitrary number, so one
is inevitably among them; INCD earns its place by making the common case a
byte cheaper. The overlap is structural and the choice is a usage question,
which is a linter's job rather than an ISA's - "DPUP.n 0d01: INCD.n does
this in a byte less" is a mechanical rule with no judgement in it.
Nothing needed re-recording, which was not a foregone conclusion: cosmosBreak
prints the system addresses the registers happened to hold, and they did not
move. Both assemblers still produce identical bytes and CosmOS still builds
itself to a fixed point.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
The quotes are gone by the time a token is classified, so checkIfKeyword's
test of token[0] == '#' matched the STRING "#Program" sitting in a program's
Data Segment. It was read as the directive: the segment silently changed in
the middle of the data, the string's nine bytes were charged to the Program
cursor instead of the Data one, and every label defined after it came out
nine bytes wrong - in a file that still had a valid header, a plausible
length, and nothing to say about any of it. The only symptom was a program
that jumped into the middle of an instruction.
This is the FOURTH of the family. A string spelling a mnemonic assembled as
that instruction; a string beginning with a zero was rejected as a malformed
literal; a string in the Program Segment was discarded in silence. The
instruction check and the literal check both carry a "not a STRING" guard
already. This one did not, so it has one now, and it lives inside
checkIfKeyword rather than at the call site so it cannot be left off again.
Nothing had ever triggered it, because nothing had ever needed a directive's
name as data. An assembler written FOR this machine necessarily does: it has
to compare tokens against "#Program" and "#Data". It was found by building
one and watching it fault on its second instruction.
Test stringKeyword puts every directive name in a program's data and prints
a label defined after them. Verified that it bites: without the fix the
assembler refuses the file outright.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
A token is classified after its quotes have been stripped, so a string
literal reading "ADD" looked exactly like the ADD instruction and was
assembled as one. It failed with "attempting to assemble outside the
Program Segment", a message about a mistake nobody had made.
The literal and label checks were already guarded against strings and the
instruction check was not. Mnemonics match without regard to case, so
"or" and "and" were caught by this too, and those are ordinary enough
words to want in a message.
Third of its family, after a string beginning with '0' being read as a
malformed number and a string in the Program Segment being silently
discarded. All three have the same root.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Anachronaut
Anachronaut