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| -rw-r--r-- | source/blog/yax/arch/rx.md | 36 |
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diff --git a/source/blog/yax/arch/rx.md b/source/blog/yax/arch/rx.md index 237d4de..1195981 100644 --- a/source/blog/yax/arch/rx.md +++ b/source/blog/yax/arch/rx.md @@ -51,6 +51,42 @@ meticulously? instruction encodings are listed in alphabetic order of instruction mnemonics. this is not amenable to writing a disassembler.. so i went through all three versions of the manual and transcribed encodings *from* the manual into a text file i could easily reorder. and so [notes/encoding_table](https://github.com/iximeow/yaxpeax-rx/blob/no-gods-no-/notes/encoding_table) was born. reorder that to be approximately by bits, and [notes/reordered_encodings](https://github.com/iximeow/yaxpeax-rx/blob/no-gods-no-/notes/reordered_encodings). finally, i tried finding patterns across encodings and simplifying the total number of encodings across all instructions, and that left me with [notes/grouped_encodings](https://github.com/iximeow/yaxpeax-rx/blob/no-gods-no-/notes/grouped_encodings). +vendors! please do not make me write things like this!! i'm not good at it!!! +``` +0 0 0 0 0 1 1 0 | mi [ opc ] ld | [ rs ] [ rd ] SUB src, dest (v1, v2, v3) + 0 0 => B 0 0 => [Rs] + 0 1 => W 0 1 => dsp:8[Rs] + 1 0 => L 1 0 => dsp:16[Rs] + 1 1 => UW 1 1 => Rs + opc={sub, cmp, add, mul, and, or, X, X, see below} + +0 0 0 0 0 1 1 0 | mi 1 0 0 0 ld | 0 0 0 [ opc ] | [ rs ] [ rd ] SBB src, dest (v1, v2, v3) + 1 0 => L + _ _ => invalid + 00 => [Rs] + 01 => dsp:8[Rs] + 10 => dsp:16[Rs] + opc={ + sbb(mi=10,ld!=11), X, adc(mi=10,ld!=11), X, + max, min, emul, emulu, + div, divu, X, X + tst, xor, X, X, + xchg, itof, X, X, + X, utof(v2, v3), X, X, + X, X, X, X, + X, X, X, X, + } + +0 0 0 0 1 [dsp] BRA.S src (v1, v2, v3) + +0 0 0 1 c [dsp] BCnd.S src (v1, v2, v3) + 0 => beq/bz (src = if dsp > 2 { dsp } else { dsp + 8 }) + 1 => bne/bnz + +0 0 1 0 [ cnd ] | [ pcdsp ] BCnd.B src (v1, v2, v3) + cnd => {eq, ne, geu, ltu, gtu, leu, pz, n, ge, lt, gt, le, o, no, bra.b, Reserved} +``` + the disassembler itself is largely transcription of this table into source code. including, unfortunately, a massive chain of if/else from `0b00000000` stopping at dozens of points on the way to `0b11111111`. :') # encoding notes |