AnachronautandClaude Opus 5
af0360128b
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
113 lines
3.2 KiB
NASM
113 lines
3.2 KiB
NASM
; The instruction set, as the assembler needs to see it.
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;
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; A SECOND COPY, and it is worth saying why rather than hoping nobody notices. The monitor
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; has one of these in cosmos.asm, and the assembler cannot use it: the monitor's copy lives
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; in the system's data at an address that moves every time CosmOS is rebuilt, and there is
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; no linker to reach it by name. So the assembler carries its own 448 bytes. That is the
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; cost of having no libraries, paid where it is cheapest to pay.
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;
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; Both copies are generated by Tests/instructiontable.py from the C assembler's own list,
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; and Tests/docs.sh checks both against it. Neither can drift without the suite saying so.
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;
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; Seven bytes an entry: the opcode, the shape, and four characters of name with the zero
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; the assembler puts after a string. Every mnemonic is four characters or fewer, so a name
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; padded to four is an exact match rather than a prefix.
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;
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; It goes in the DATA Segment, because the assembler has to read it and an instruction can
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; only read Data Memory. A table in Program Memory could not be reached by the program
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; holding it, except through the memory controller.
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#Data
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; How many bytes an instruction of each shape runs to, the opcode included. The assembler
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; does not use this to size a token - the operand that follows is a token of its own and
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; carries its own length - but it is what says an instruction is well formed.
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AsmShapeLength:
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0d1 0d3 0d2 0d2 0d3 0d4 0d3
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; How many Data Pointer selectors an instruction of each shape names. This is what the
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; assembler needs: a selector is part of the mnemonic rather than a token after it, so it
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; is the one thing about an instruction's length that is not settled by the opcode alone.
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;
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; 0 no operand 4 a selector and a byte
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; 1 an address 5 a selector and an address, which is SETD
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; 2 a byte 6 two selectors, which is LDD and STD
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; 3 a selector
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AsmShapeSelectors:
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0d0 0d0 0d0 0d1 0d1 0d1 0d2
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AsmInstructionCount:
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0d70
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AsmInstructions:
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0x00 0d0 "ADD "
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0x01 0d0 "SUB "
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0x02 0d0 "AND "
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0x03 0d0 "OR "
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0x04 0d0 "XOR "
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0x05 0d0 "NOTA"
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0x06 0d0 "NOTB"
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0x07 0d0 "SHL "
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0x08 0d0 "SHR "
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0x10 0d1 "BRI "
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0x11 0d1 "BRQ "
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0x12 0d1 "BRA "
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0x13 0d1 "BRB "
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0x14 0d1 "BRC "
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0x15 0d3 "BRD "
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0x1A 0d1 "BNQ "
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0x1B 0d1 "BNA "
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0x1C 0d1 "BNB "
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0x1D 0d1 "BNC "
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0x16 0d1 "RCAL"
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0x17 0d1 "CALL"
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0x18 0d2 "SWI "
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0x19 0d0 "RETI"
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0x1E 0d0 "RRET"
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0x1F 0d0 "RET "
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0x20 0d0 "RSTA"
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0x21 0d0 "RSTB"
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0x22 0d0 "INCA"
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0x23 0d0 "INCB"
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0x24 0d0 "DECA"
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0x25 0d0 "DECB"
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0x26 0d2 "INIA"
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0x27 0d2 "INIB"
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0x28 0d0 "CCF "
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0x29 0d0 "MVQA"
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0x2A 0d0 "MVQB"
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0x2B 0d0 "SIF "
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0x2C 0d0 "CIF "
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0x30 0d0 "PSHQ"
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0x31 0d0 "PSHA"
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0x32 0d0 "PSHB"
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0x33 0d3 "PSHD"
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0x34 0d0 "POPA"
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0x35 0d0 "POPB"
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0x36 0d3 "POPD"
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0x40 0d3 "INCD"
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0x41 0d3 "DECD"
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0x42 0d3 "LDA "
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0x43 0d3 "LDB "
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0x44 0d3 "STQ "
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0x45 0d3 "STA "
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0x46 0d3 "STB "
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0x47 0d5 "SETD"
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0x48 0d4 "DPUP"
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0x49 0d4 "DPDN"
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0x4A 0d6 "LDD "
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0x4B 0d6 "STD "
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0x4C 0d3 "MVSD"
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0x4D 0d3 "MVDS"
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0x4E 0d3 "DPUA"
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0x4F 0d3 "DPDA"
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0x50 0d3 "DPUW"
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0x51 0d3 "DPDW"
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0xD0 0d2 "OUTQ"
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0xD1 0d2 "OUTA"
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0xD2 0d2 "OUTB"
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0xE0 0d2 "INA "
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0xE1 0d2 "INB "
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0xF0 0d0 "NOP "
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0xFF 0d0 "HALT"
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