Anachronaut
cd5f548736
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.
114 lines
3.2 KiB
NASM
114 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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0d71
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AsmInstructions:
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0x10 0d0 "ADD "
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0x11 0d0 "SUB "
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0x12 0d0 "AND "
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0x13 0d0 "OR "
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0x14 0d0 "XOR "
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0x15 0d0 "NOTA"
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0x16 0d0 "NOTB"
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0x17 0d0 "SHL "
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0x18 0d0 "SHR "
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0x60 0d1 "BRI "
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0x61 0d1 "BRQ "
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0x62 0d1 "BRA "
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0x63 0d1 "BRB "
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0x64 0d1 "BRC "
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0x65 0d3 "BRD "
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0x66 0d1 "BNQ "
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0x67 0d1 "BNA "
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0x68 0d1 "BNB "
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0x69 0d1 "BNC "
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0x70 0d1 "RCAL"
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0x71 0d1 "CALL"
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0x72 0d2 "SWI "
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0x73 0d0 "RETI"
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0x74 0d0 "RRET"
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0x75 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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0xFE 0d0 "WAIT"
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0xFF 0d0 "HALT"
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