[cctalk] IEEE Std 694-1985 Microprocessor Assembly Language - a precis

On 21/1/24 06:08, Paul Koning wrote: That was mentioned as a contentious issue. Fischer (December 1979) "Special Feature: Microprocessor Assembly Language Draft Standard" Computer 12(12) pp. 96–109 doi:10.1109/MC.1979.1658582. Baldwin, G. (August 1984) "Towards an Assembly Language Standard" IEEE Micro 4(4) pp. 81–85 doi:10.1109/MM.1984.291223 "IEEE Standard for Microprocessor Assembly Language" IEEE Std 694-1985 1985 doi:10.1109/IEEESTD.1985.81632 The standard was withdrawn in 2001. None of the articles are freely available. The standard is 19 pages in the PDF. If the effort started in 1976-7, and if it got a reasonable way, may be a samizdat copy in the late 70s might have made a difference. A precis of the standard, using brace expansion, with brackets for optional  & some C stuff. 3.12 Mnemonics: Begin with letter from a verb, no embedding of addressing modes or operand designations. Mnemonics & operands may have types indicated by a suffix ie I single bit I(\d+) ie I1, I18 bit field B: byte  == I8 S: short == I16 == B2 L: long  == I32 == B4 == S2 Q: quad  == I64 == B8 == S4 == I2 F for floating pt, FS, FL, FX, FP for the IEEE 754-1985 types D for decimal, so maybe DP for packed decimal Example: CVT.FS .D2.L => Convert int32_t in register D2 to short float As I read it, unless overriden by an assembler directive, the suffixes must be used only when needed. As a teaching tool or an Esparanto in a disassembler the redundancy could help. {ADD,SUB,MUL,DIV}[{U,S}] In general, the destination operand is the first operand. {ADD,SUB}C {INC,DEC} So the DG Eclipse WINC mnemonic would be INC .register.L {CMP,TEST{,SET},NEG,ADJ,CVT,AND,OR,XOR,NOT,{SET,CLR}[{C,V]},{SHL,SHR}{,A}} {ROL,ROR{,C},FILL,PUSH,POP,XCH,IN,OUT} {LD,ST} MOVE ; The destination operand is usually the first operand to match SUB A,B == A -= B ; The exceptions are the ST, MOVE and OUT instructions {,D,I}{BR,B{Z,NZ,E,NE,GT,GE,LT,LE,H,NH,L,NL,C,NC,P,NP,N,NN,V,NV,PE,PO,T,F}} {CALL,RET,RETI,RETSKIP,SKIP,BRK,CC,EI,DI,ENTER,EXIT,EXT,HALT,INS,NOP,TR,WAIT} 4.4.1 Operators, no surprises to a C programmer except for ~ as exclusive or instead of C's ^ 4.5.1 Numeric constants, default to decimal if the RADIX directive isn't used. Otherwise {B,D,H,Q}'digits, respectively Binary, Decimal, Hex and Octal So ASCII ESC has the value     B'11011' = Q'33 = D'27 = H'1B 4.7.1 Address space operators # prefix => literal / prefix => direct address . prefix => register $ prefix => PC relative Without a prefix, the implementor-defined default addressing mode ! prefix => direct page (base page) For segmented addresses the segment precedes the !  ie CODE!100 [] for indexing and indirect addressing. Like operand suffixes or size or type, scaling uses the suffix with a : separator. Size precedes scaling when both are needed, ie A[.3.S:L] => int16_t reg3; int32_t A[]; A[reg3]; 4.7.4 Autoincrement & autodecrement => prefixes or suffixes When a suffix the scaling suffix is last  ie .A2--:L     => post-decrement register A2 by 4 When a prefix the scaling suffix is prefixed first  ie :S++.B     => pre-increment register B by 2 --Aside there's a bit of a byte-addressed assumption there, in the examples. The HP 3000 had different pointer types for bytes and larger objects, essentially (char *)&an_int16 == (&an_int16) << 1; Though an assembler might be able to track the type of objects. I think the Motorola 88000 used IEEE Assembler, but don't remember other uptakes. No DG Aviion stuff on BitSavers that I can see. While I used a little assembler on MSDOS, DG AOS/VS, Vax VMS, mostly C was to the fore. So I saw assembler mainly in gdb or other debugger's disassembly. The HP 3000 could pack 2 stack-ops into 1 16-bit instruction & the RTX 20x0 ALU instruction format http://users.ece.cmu.edu/~koopman/stack_computers/sec4_5.html#453 Figure 4.9(c) gives a possible NOT, Shift & RET as part of the instruction. I'd guess the itanic would also be uncomfortable, I admit I've avoided even looking at it's disassembled code. Fig 1 1984 article. 6502 example -- LD   .X,/INDEX ; Load 8-bit index into register X.         ;; LDX  INDEX DEC  .X        ; Offsets start at 0, not 1.                ;; DEX MOVE .X, .A    ; Move value to accumulator.                ;; TXA SHL  .A        ; Double it to form offset,                 ;; ASL  A                ;  since table entries are 2 bytes long. MOVE .A, .X    ; Move offset into index register X.        ;; TAX LD   .A,/GOTO[.X]       ; Get first byte                   ;; LDA  GOTO,X                         ;  of destination address. ST   .A,/INDIRECT    ; Store it in target address holder.  ;; STA  INDIRECT LD   .A,(/GOTO + 1)[.X] ; Likewise for second              ;; LDA  GOTO + 1,X ST   .A,/INDIRECT + 1   ; byte.                            ;; STA  INDIRECT+ 1 BR   [/INDIRECT]        ; Branch indirectly.               ;; JMP  (INDIRECT) From L. Leventhal and W. Saville, 6502 Assembly Language Subroutines, C 1982 The Cygnus/Redhat cgen software generates simulators, assembler (GNU) and disassembles from a guile (scheme) description of the instruction set architecture. Perhaps it could have been enhanced to cope with multiple forms, so the assembler & disassembler could have chosen IEEE or manufacturer style.