SplitBit assembles SplitBit: M1, a single file with no includes
Programs/CosmOS/Assembler/ is an assembler written in SplitBit assembly. It
runs under CosmOS, reads source off a SplitBit disk, and writes a binary back
to it with no host involved anywhere:
> run Asm.sbx hello.asm
wrote hello.bin: program 17, data 14, labels 2
THE ACCEPTANCE TEST IS THE BYTES. Tests/native.sh assembles Programs/hello.asm
both ways and compares the two files byte for byte, then runs the one the
machine built. "It ran" and "the sizes look right" both pass for a binary with
a label one byte out, which is a program that jumps into the middle of an
instruction - so the only honest test is the one SplitDisk and sbfs.asm
already work under: two implementations of one written specification, each
checking the other. The files are identical and the result prints Hello,
World! in 70 cycles.
hello.asm is the target because it is the oldest program in the repository.
The first thing this machine ever ran is now the first thing it assembles for
itself.
TWO PASSES OVER STREAMED SOURCE. The C assembler reads every token of every
file into one array; that cannot port, because cosmos.asm alone is 56,047
bytes against 64K of Data Memory. The native one streams through a 256 byte
window, twice, and keeps only the label table between the passes. Two passes
suffice because every length is known without resolving anything - an
instruction's from its shape, a value's is one, a string's is its characters
and a zero - so the first pass fixes every address and the second never needs
a fixup list. A forward reference stops being a special case and becomes the
reason there are two passes at all.
The parts, each checked before anything was built on it:
source.asm characters out of a file of any size, with a line number
token.asm tokens out of characters, one character of lookahead
classify.asm what a token is, in the C assembler's order, which IS the
language: keyword, instruction, value, string, label
labels.asm names packed in an arena, four bytes of index each
numbers.asm sixteen bit arithmetic, since sbfs.asm's cannot be reached
table.asm the instruction set, generated by the same script the
monitor's copy is, and now BOTH are checked by docs.sh
readTest.asm and tokenTest.asm check the reader and the tokenizer on their
own, recorded as cosmosSource and cosmosTokens. A wrong classification does
not produce a wrong byte somewhere obvious; it produces a right looking
program of the wrong length, so it is worth catching where it happens.
WHAT IT REFUSES: #Include, #Base, #Align, #Reserve and #Vectors are refused
by name rather than ignored. Skipping a directive would produce a file that
looked right and was the wrong length, which is the worst thing an assembler
can do.
Two traps worth recording, both already known to this project and both hit
again: CALL restores A, B and DP0-DP2, so three routines returning an answer
in A had it undone by their own return; and numStep works on DP0, so three
sites that set DP1 left a pointer that never advanced.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
co-authored by
Claude Opus 5
Claude Opus 5
parent
a131a90c67
commit
dcb331c151
@@ -0,0 +1,178 @@
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; The assembler's front end on its own, one line per token.
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;
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; Prints the line each token started on, what the token turned out to be, how many bytes
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; it will come to, and the token itself between brackets so that whitespace at either end
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; would show if any ever leaked in.
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;
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; WHAT A TOKEN IS is the part worth checking here rather than at the far end. A wrong
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; classification does not produce a wrong byte in an obvious place - it produces a right
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; looking program of the wrong length, with everything after it shifted, and by then the
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; only symptom is that a label points at the middle of an instruction.
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;
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; Written by Anachronaut
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#Include services.asm
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#Program
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#Base 0x2000
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start:
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SETD.0 Wanted
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INIB 0d23
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SWI osArgument
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SETD.0 Wanted
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LDA.0
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BRA nothingAsked
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SETD.0 Wanted
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CALL srcOpen
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BNQ noFile
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tokenLoop:
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CALL tokNext
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BNQ tokensDone
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SETD.0 TokLine
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LDA.0
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INCD.0
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LDB.0
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SWI osPrintNumber
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CALL clsToken
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BNQ badToken
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; Which of the six it turned out to be. The names are four characters and a space, so
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; the columns line up without any counting.
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SETD.0 TypeNames
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SETD.2 ClsType
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LDA.2
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CALL nameOfType
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SETD.1 NamePointer
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LDD.0.1
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SWI osPrintString
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SETD.0 ClsLength
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LDA.0
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RSTB
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PSHA
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POPB
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RSTA
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SWI osPrintNumber
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SETD.0 OpenMark
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SWI osPrintString
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SETD.0 TokText
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SWI osPrintString
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SETD.0 CloseMark
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SWI osPrintString
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BRI tokenLoop
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badToken:
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SETD.0 StoppedText
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SWI osPrintString
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SWI osExit
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; The name of type A, out of a table of fixed width entries so that no pointer arithmetic
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; is needed beyond a multiply by the width.
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nameOfType:
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SETD.0 TypeWidth
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LDB.0
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RSTA
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SETD.0 NameLeft
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STA.0
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SETD.2 ClsType
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LDA.2
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SETD.0 NameOffset
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CALL numZero
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nameLoop:
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SETD.2 ClsType
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LDA.2
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SETD.0 NameLeft
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LDB.0
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CCF
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SUB
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BRQ nameFound
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SETD.0 TypeWidth
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LDA.0
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SETD.0 NameOffset
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CALL numAddByte
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SETD.0 NameLeft
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LDA.0
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INCA
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STA.0
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BRI nameLoop
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nameFound:
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; The answer is left in NamePointer rather than in DP0, because a RET puts Data Pointers
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; 0 to 2 back as they were: a routine cannot hand back a pointer, only write one down.
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SETD.0 TypeNames
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SETD.1 NamePointer
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STD.0.1
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SETD.0 NamePointer
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SETD.2 NameOffset
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CALL numAdd
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RET
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tokensDone:
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SETD.0 DoneText
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SWI osPrintString
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SWI osExit
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nothingAsked:
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SETD.0 AskText
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SWI osPrintString
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SWI osExit
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noFile:
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SETD.0 NoFileText
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SWI osPrintString
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SWI osExit
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#Data
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#Base 0x1000
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Wanted:
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#Reserve 0d23
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OpenMark:
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" ["
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CloseMark:
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"]
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"
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; Six names of eleven characters each, counting the zero the assembler puts on the end of
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; every string. Written one to a line so that adding a type is adding a line.
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TypeNames:
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" keyword "
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" instr "
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" value "
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" string "
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" label: "
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" label "
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TypeWidth:
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0d11
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NameLeft:
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0x00
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NameOffset:
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0x00 0x00
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NamePointer:
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0x00 0x00
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StoppedText:
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"---- stopped: the assembler does not understand that
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"
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DoneText:
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"---- no more tokens
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"
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AskText:
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"say which file
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"
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NoFileText:
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"no such file
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"
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#Include numbers.asm
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#Include source.asm
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#Include token.asm
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#Include classify.asm
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#Include table.asm
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