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.
-S writes every label and the address it was given, in address order.
Nothing else knows that. A program on the disk is bytes; the monitor can
disassemble it but has no idea what any of it is called. So counting which
addresses a program calls says a great deal and names nothing - the answer
arrives as a column of numbers and somebody works out by hand which routine
each one is inside.
It was deferred when the native assembler was planned, as a listing and symbol
dump nobody needed yet. Finding out where the assembler spends its time is what
needed it: the top six call targets were addresses until this existed and are
numStep, numCompare, tokGet, srcNext, numAddByte and clsSameName with it.
Sorted by address rather than by name, because the question asked of it is
always "what is at this address".
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
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
It always wrote .bin, whatever it had built. So assembling a loadable
program without -o produced Say.bin containing SBEX - a boot image name on a
file the machine cannot boot, in a repository whose whole convention is that
a .bin is started from and a .sbx is loaded.
Successfully wrote SplitBit boot image to "hello.bin".
Successfully wrote SplitBit loadable program to "Say.sbx".
programIsLoadable() already existed and is already what decides which
writer runs; the name now asks it too. Nothing in the build depended on the
old behaviour, because everything that assembles anything passes -o.
THE ASSEMBLER THAT RUNS ON SPLITBIT ALREADY DID IT THIS WAY. Two assemblers
naming their output differently from the same source is exactly the kind of
difference that wastes an afternoon, and the newer one was right.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
"Binary" was doing three jobs. It meant an SPBT file that the machine starts
from; it meant whatever the assembler happened to produce, which is now
either that or a loadable program; and it meant a compiled host tool. A word
that means three things means none of them, and the first of the three has a
name already - this project has been calling them boot images for a while
and the manuals had not caught up.
Where it means an SPBT file -> boot image
Where it means either output -> output
Where it means a host executable -> left alone
Where it means base two -> left alone
The user facing messages move with it:
Error: No boot image specified.
Usage: ./SplitBit [OPTIONS] <boot image>
Error: This is not a SplitBit boot image.
Error: This boot image is in format version 2, and this emulator reads 1.
Successfully wrote SplitBit boot image to "hello.bin".
The assembler's own help was the interesting case. Its -o writes either
format, so "the binary" there was never right - it is "the output" now, and
the message that names the format is the one that says which it wrote.
No recorded output contained the word, so nothing needed re-blessing.
Checked before starting rather than after.
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>
The loadable program format's header has been in the working tree since
the loader was written and has never been in the repository: the gitignore
rules matched Source/Assembler as a directory, so it was silently
untracked. Anything cloning this repository could not build it, because
secondPass.c includes this file.
This is the failure the previous commit describes, having already happened
once without being noticed.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Added DPUP and DPDN, which take a one byte operand specifying how far up or down to offset the Data Pointer.
Three Fibonacci generators using the print.asm library.
- 8 bit values printing in decimal representation.
- 16 bit values printing in hexadecimal representation.
- 32 bit values printing in hexadecimal representation.
Anachronaut
Anachronaut