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collapseos/apps/zasm/avr.asm
Virgil Dupras 97dcad9b15 recipes/sms/kbd: use Collapse OS' AVR assembler
2020-02-26 23:10:43 -05:00

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19 KiB
NASM
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; Same thing as instr.asm, but for AVR instructions
; *** Instructions table ***
; List of mnemonic names separated by a null terminator. Their index in the
; list is their ID. Unlike in zasm, not all mnemonics have constant associated
; to it because it's generally not needed. This list is grouped by argument
; categories, and then alphabetically. Categories are ordered so that the 8bit
; opcodes come first, then the 16bit ones. 0xff ends the chain
instrNames:
; Branching instructions. They are all shortcuts to BRBC/BRBS. These are not in
; alphabetical order, but rather in "bit order". All "bit set" instructions
; first (10th bit clear), then all "bit clear" ones (10th bit set). Inside this
; order, they're then in "sss" order (bit number alias for BRBC/BRBS).
.db "BRCS", 0
.db "BREQ", 0
.db "BRMI", 0
.db "BRVS", 0
.db "BRLT", 0
.db "BRHS", 0
.db "BRTS", 0
.db "BRIE", 0
.db "BRCC", 0
.db "BRNE", 0
.db "BRPL", 0
.db "BRVC", 0
.db "BRGE", 0
.db "BRHC", 0
.db "BRTC", 0
.db "BRID", 0
.equ I_BRBS 16
.db "BRBS", 0
.db "BRBC", 0
.equ I_LD 18
.db "LD", 0
.db "ST", 0
; Rd(5) + Rr(5) (from here, instrTbl8)
.equ I_ADC 20
.db "ADC", 0
.db "ADD", 0
.db "AND", 0
.db "ASR", 0
.db "BCLR", 0
.db "BLD", 0
.db "BREAK", 0
.db "BSET", 0
.db "BST", 0
.db "CLC", 0
.db "CLH", 0
.db "CLI", 0
.db "CLN", 0
.db "CLR", 0
.db "CLS", 0
.db "CLT", 0
.db "CLV", 0
.db "CLZ", 0
.db "COM", 0
.db "CP", 0
.db "CPC", 0
.db "CPSE", 0
.db "DEC", 0
.db "EICALL", 0
.db "EIJMP", 0
.db "EOR", 0
.db "ICALL", 0
.db "IJMP", 0
.db "IN", 0
.db "INC", 0
.db "LAC", 0
.db "LAS", 0
.db "LAT", 0
.db "LSL", 0
.db "LSR", 0
.db "MOV", 0
.db "MUL", 0
.db "NEG", 0
.db "NOP", 0
.db "OR", 0
.db "OUT", 0
.db "POP", 0
.db "PUSH", 0
.db "RET", 0
.db "RETI", 0
.db "ROR", 0
.db "SBC", 0
.db "SBRC", 0
.db "SBRS", 0
.db "SEC", 0
.db "SEH", 0
.db "SEI", 0
.db "SEN", 0
.db "SER", 0
.db "SES", 0
.db "SET", 0
.db "SEV", 0
.db "SEZ", 0
.db "SLEEP", 0
.db "SUB", 0
.db "SWAP", 0
.db "TST", 0
.db "WDR", 0
.db "XCH", 0
.equ I_ANDI 84
.db "ANDI", 0
.db "CBR", 0
.db "CPI", 0
.db "LDI", 0
.db "ORI", 0
.db "SBCI", 0
.db "SBR", 0
.db "SUBI", 0
.equ I_RCALL 92
.db "RCALL", 0
.db "RJMP", 0
.equ I_CBI 94
.db "CBI", 0
.db "SBI", 0
.db "SBIC", 0
.db "SBIS", 0
; 32-bit
; ZASM limitation: CALL and JMP constants are 22-bit. In ZASM, we limit
; ourselves to 16-bit. Supporting 22-bit would incur a prohibitive complexity
; cost. As they say, 64K words ought to be enough for anybody.
.equ I_CALL 98
.db "CALL", 0
.db "JMP", 0
.db 0xff
; Instruction table
;
; A table row starts with the "argspecs+flags" byte, followed by two upcode
; bytes.
;
; The argspecs+flags byte is separated in two nibbles: Low nibble is a 4bit
; index (1-based, 0 means no arg) in the argSpecs table. High nibble is for
; flags. Meaning:
;
; Bit 7: Arguments swapped. For example, if we have this bit set on the argspec
; row 'A', 'R', then what will actually be read is 'R', 'A'. The
; arguments destination will be, hum, de-swapped, that is, 'A' is going
; in H and 'R' is going in L. This is used, for example, with IN and OUT.
; IN has a Rd(5), A(6) signature. OUT could have the same signature, but
; AVR's mnemonics has those args reversed for more consistency
; (destination is always the first arg). The goal of this flag is to
; allow this kind of syntactic sugar with minimal complexity.
;
; Bit 6: Second arg is a copy of the first
; Bit 5: Second arg is inverted (complement)
; In the same order as in instrNames
instrTbl:
; Regular processing: Rd with second arg having its 4 low bits placed in C's
; 3:0 bits and the 4 high bits being place in B's 4:1 bits
; No args are also there.
.db 0x02, 0b00011100, 0x00 ; ADC Rd, Rr
.db 0x02, 0b00001100, 0x00 ; ADD Rd, Rr
.db 0x02, 0b00100000, 0x00 ; AND Rd, Rr
.db 0x01, 0b10010100, 0b00000101 ; ASR Rd
.db 0x0b, 0b10010100, 0b10001000 ; BCLR s, k
.db 0x05, 0b11111000, 0x00 ; BLD Rd, b
.db 0x00, 0b10010101, 0b10011000 ; BREAK
.db 0x0b, 0b10010100, 0b00001000 ; BSET s, k
.db 0x05, 0b11111010, 0x00 ; BST Rd, b
.db 0x00, 0b10010100, 0b10001000 ; CLC
.db 0x00, 0b10010100, 0b11011000 ; CLH
.db 0x00, 0b10010100, 0b11111000 ; CLI
.db 0x00, 0b10010100, 0b10101000 ; CLN
.db 0x41, 0b00100100, 0x00 ; CLR Rd (Bit 6)
.db 0x00, 0b10010100, 0b11001000 ; CLS
.db 0x00, 0b10010100, 0b11101000 ; CLT
.db 0x00, 0b10010100, 0b10111000 ; CLV
.db 0x00, 0b10010100, 0b10011000 ; CLZ
.db 0x01, 0b10010100, 0b00000000 ; COM Rd
.db 0x02, 0b00010100, 0x00 ; CP Rd, Rr
.db 0x02, 0b00000100, 0x00 ; CPC Rd, Rr
.db 0x02, 0b00010000, 0x00 ; CPSE Rd, Rr
.db 0x01, 0b10010100, 0b00001010 ; DEC Rd
.db 0x00, 0b10010101, 0b00011001 ; EICALL
.db 0x00, 0b10010100, 0b00011001 ; EIJMP
.db 0x02, 0b00100100, 0x00 ; EOR Rd, Rr
.db 0x00, 0b10010101, 0b00001001 ; ICALL
.db 0x00, 0b10010100, 0b00001001 ; IJMP
.db 0x07, 0b10110000, 0x00 ; IN Rd, A
.db 0x01, 0b10010100, 0b00000011 ; INC Rd
.db 0x01, 0b10010010, 0b00000110 ; LAC Rd
.db 0x01, 0b10010010, 0b00000101 ; LAS Rd
.db 0x01, 0b10010010, 0b00000111 ; LAT Rd
.db 0x41, 0b00001100, 0x00 ; LSL Rd
.db 0x01, 0b10010100, 0b00000110 ; LSR Rd
.db 0x02, 0b00101100, 0x00 ; MOV Rd, Rr
.db 0x02, 0b10011100, 0x00 ; MUL Rd, Rr
.db 0x01, 0b10010100, 0b00000001 ; NEG Rd
.db 0x00, 0b00000000, 0b00000000 ; NOP
.db 0x02, 0b00101000, 0x00 ; OR Rd, Rr
.db 0x87, 0b10111000, 0x00 ; OUT A, Rr (Bit 7)
.db 0x01, 0b10010000, 0b00001111 ; POP Rd
.db 0x01, 0b10010010, 0b00001111 ; PUSH Rd
.db 0x00, 0b10010101, 0b00001000 ; RET
.db 0x00, 0b10010101, 0b00011000 ; RETI
.db 0x01, 0b10010100, 0b00000111 ; ROR Rd
.db 0x02, 0b00001000, 0x00 ; SBC Rd, Rr
.db 0x05, 0b11111100, 0x00 ; SBRC Rd, b
.db 0x05, 0b11111110, 0x00 ; SBRS Rd, b
.db 0x00, 0b10010100, 0b00001000 ; SEC
.db 0x00, 0b10010100, 0b01011000 ; SEH
.db 0x00, 0b10010100, 0b01111000 ; SEI
.db 0x00, 0b10010100, 0b00101000 ; SEN
.db 0x0a, 0b11101111, 0b00001111 ; SER Rd
.db 0x00, 0b10010100, 0b01001000 ; SES
.db 0x00, 0b10010100, 0b01101000 ; SET
.db 0x00, 0b10010100, 0b00111000 ; SEV
.db 0x00, 0b10010100, 0b00011000 ; SEZ
.db 0x00, 0b10010101, 0b10001000 ; SLEEP
.db 0x02, 0b00011000, 0x00 ; SUB Rd, Rr
.db 0x01, 0b10010100, 0b00000010 ; SWAP Rd
.db 0x41, 0b00100000, 0x00 ; TST Rd (Bit 6)
.db 0x00, 0b10010101, 0b10101000 ; WDR
.db 0x01, 0b10010010, 0b00000100 ; XCH Rd
; Rd(4) + K(8): XXXXKKKK ddddKKKK
.db 0x04, 0b01110000, 0x00 ; ANDI Rd, K
.db 0x24, 0b01110000, 0x00 ; CBR Rd, K (Bit 5)
.db 0x04, 0b00110000, 0x00 ; CPI Rd, K
.db 0x04, 0b11100000, 0x00 ; LDI Rd, K
.db 0x04, 0b01100000, 0x00 ; ORI Rd, K
.db 0x04, 0b01000000, 0x00 ; SBCI Rd, K
.db 0x04, 0b01100000, 0x00 ; SBR Rd, K
.db 0x04, 0b01010000, 0x00 ; SUBI Rd, K
; k(12): XXXXkkkk kkkkkkkk
.db 0x08, 0b11010000, 0x00 ; RCALL k
.db 0x08, 0b11000000, 0x00 ; RJMP k
; A(5) + bit: XXXXXXXX AAAAAbbb
.db 0x09, 0b10011000, 0x00 ; CBI A, b
.db 0x09, 0b10011010, 0x00 ; SBI A, b
.db 0x09, 0b10011001, 0x00 ; SBIC A, b
.db 0x09, 0b10011011, 0x00 ; SBIS A, b
; k(16) (well, k(22)...)
.db 0x08, 0b10010100, 0b00001110 ; CALL k
.db 0x08, 0b10010100, 0b00001100 ; JMP k
; Same signature as getInstID in instr.asm
; Reads string in (HL) and returns the corresponding ID (I_*) in A. Sets Z if
; there's a match.
getInstID:
push bc
push hl
push de
ex de, hl ; DE makes a better needle
; haystack. -1 because we inc HL at the beginning of the loop
ld hl, instrNames-1
ld b, 0xff ; index counter
.loop:
inc b
inc hl
ld a, (hl)
inc a ; check if 0xff
jr z, .notFound
call strcmpIN
jr nz, .loop
; found!
ld a, b ; index
cp a ; ensure Z
.end:
pop de
pop hl
pop bc
ret
.notFound:
dec a ; unset Z
jr .end
; Same signature as parseInstruction in instr.asm
; Parse instruction specified in A (I_* const) with args in I/O and write
; resulting opcode(s) in I/O.
; Sets Z on success. On error, A contains an error code (ERR_*)
parseInstruction:
; *** Step 1: initialization
; Except setting up our registers, we also check if our index < I_ADC.
; If we are, we skip regular processing for the .BR processing, which
; is a bit special.
; During this processing, BC is used as the "upcode WIP" register. It's
; there that we send our partial values until they're ready to spit to
; I/O.
ld bc, 0
ld e, a ; Let's keep that instrID somewhere safe
; First, let's fetch our table row
cp I_LD
jp c, .BR ; BR is special, no table row
jp z, .LD ; LD is special
cp I_ADC
jp c, .ST ; ST is special
; *** Step 2: parse arguments
sub I_ADC ; Adjust index for table
; Our row is at instrTbl + (A * 3)
ld hl, instrTbl
call addHL
sla a ; A * 2
call addHL ; (HL) is our row
ld a, (hl)
push hl \ pop ix ; IX is now our tblrow
ld hl, 0
or a
jp z, .spit ; No arg? spit right away
and 0xf ; lower nibble
dec a ; argspec index is 1-based
ld hl, argSpecs
sla a ; A * 2
call addHL ; (HL) is argspec row
ld d, (hl)
inc hl
ld a, (hl)
ld h, d
ld l, a ; H and L contain specs now
bit 7, (ix)
call nz, .swapHL ; Bit 7 set, swap H and L
call _parseArgs
ret nz
; *** Step 3: place arguments in binary upcode and spit.
; (IX) is table row
; Parse arg values now in H and L
; InstrID is E
bit 7, (ix)
call nz, .swapHL ; Bit 7 set, swap H and L again!
bit 6, (ix)
call nz, .cpHintoL ; Bit 6 set, copy H into L
bit 5, (ix)
call nz, .invL ; Bit 5 set, invert L
ld a, e ; InstrID
cp I_ANDI
jr c, .spitRegular
cp I_RCALL
jr c, .spitRdK8
cp I_CBI
jr c, .spitk12
cp I_CALL
jr c, .spitA5Bit
; Spit k(16)
call .spit ; spit 16-bit const upcode
; divide HL by 2 (PC deals with words, not bytes)
srl h \ rr l
; spit 16-bit K, LSB first
ld a, l
call ioPutB
ld a, h
jp ioPutB
.spitRegular:
; Regular process which places H and L, ORring it with upcode. Works
; in most cases.
call .placeRd
call .placeRr
jr .spit
.spitRdK8:
call .placeRd
call .placeRr
rr b ; K(8) start at B's 1st bit, not 2nd
jr .spit
.spitk12:
; k(12) in HL
; We're doing the same dance as in _readk7. See comments there.
call zasmIsFirstPass
jr z, .spit
ld de, 0xfff
add hl, de
jp c, unsetZ ; Carry? number is way too high.
ex de, hl
call zasmGetPC ; --> HL
inc hl \ inc hl
ex de, hl
sbc hl, de
jp c, unsetZ ; Carry? error
ld de, 0xfff
sbc hl, de
; We're within bounds! Now, divide by 2
ld a, l
rr h \ rra
; LSB in A
ld c, a
ld a, h
and 0xf
ld b, a
jr .spit
.spitA5Bit:
ld a, h
sla a \ rla \ rla
or l
ld c, a
jr .spit
.spit:
; LSB is spit *before* MSB
ld a, (ix+2)
or c
call ioPutB
.spitMSB:
ld a, (ix+1)
or b
call ioPutB
xor a ; ensure Z, set success
ret
; Spit a branching mnemonic.
.BR:
; While we have our index in A, let's settle B straight: Our base
; upcode is 0b11110000 for "bit set" types and 0b11110100 for "bit
; clear" types. However, we'll have 2 left shift operation done on B
; later on, so we need those bits shifted right.
ld b, 0b111100
cp I_BRBS
jr z, .rdBRBS
jr nc, .rdBRBC
; We have an alias. Our "sss" value is index & 0b111
; Before we get rid of that 3rd bit, let's see, is it set? if yes, we'll
; want to increase B
bit 3, a
jr z, .skip1 ; 3rd bit unset
inc b
.skip1:
and 0b111
ld c, a ; can't store in H now, (HL) is used
ld h, 7
ld l, 0
call _parseArgs
ret nz
; ok, now we can
ld l, h ; k in L
ld h, c ; bit in H
.spitBR2:
; bit in H, k in L.
; Our value in L is the number of relative *bytes*. The value we put
; there is the number of words. Therefore, relevant bits are 7:1
ld a, l
sla a \ rl b
sla a \ rl b
and 0b11111000
; k is now shifted by 3, two of those bits being in B. Let's OR A and
; H and we have our LSB ready to go.
or h
call ioPutB
; Good! MSB now. B is already good to go.
ld a, b
jp ioPutB
.rdBRBC:
; In addition to reading "sss", we also need to inc B so that our base
; upcode becomes 0b111101
inc b
.rdBRBS:
ld h, 'b'
ld l, 7
call _parseArgs
ret nz
; bit in H, k in L.
jr .spitBR2
.LD:
ld h, 'R'
ld l, 'z'
call _parseArgs
ret nz
ld d, 0b10000000
jr .LDST
.ST:
ld h, 'z'
ld l, 'R'
call _parseArgs
ret nz
ld d, 0b10000010
call .swapHL
; continue to .LDST
.LDST:
; Rd in H, Z in L, base upcode in D
call .placeRd
; We're spitting LSB first, so let's compose it.
ld a, l
and 0b00001111
or c
call ioPutB
; Now, MSB's bit 4 is L's bit 4. How convenient!
ld a, l
and 0b00010000
or d
or b
; MSB composed!
call ioPutB
cp a ; ensure Z
ret
; local routines
; place number in H in BC at position .......d dddd....
; BC is assumed to be 0
.placeRd:
sla h \ rl h \ rl h \ rl h ; last RL H might set carry
rl b
ld c, h
ret
; place number in L in BC at position ...rrrr. ....rrrr
; BC is assumed to be either 0 or to be set by .placeRd, that is, that the
; high 4 bits of C and lowest bit of B will be preserved.
.placeRr:
; let's start with the 4 lower bits
ld a, l
and 0x0f
or c
ld c, a
ld a, l
; and now those high 4 bits which go in B.
and 0xf0
rra \ rra \ rra
or b
ld b, a
ret
.swapHL:
ld a, h
ld h, l
ld l, a
ret
.cpHintoL:
ld l, h
ret
.invL:
ld a, l
cpl
ld l, a
ret
; Argspecs: two bytes describing the arguments that are accepted. Possible
; values:
;
; 0 - None
; 7 - a k(7) address, relative to PC, *in bytes* (divide by 2 before writing)
; 8 - a K(8) value
; 'a' - A 5-bit I/O port value
; 'A' - A 6-bit I/O port value
; 'b' - a 0-7 bit value
; 'D' - A double-length number which will fill whole HL.
; 'R' - an r5 value: r0-r31
; 'r' - an r4 value: r16-r31
; 'z' - an indirect register (X, Y or Z), with our without post-inc/pre-dec
; indicator. This will result in a 5-bit number, from which we can place
; bits 3:0 to upcode's 3:0 and bit 4 at upcode's 12 in LD and ST.
;
; All arguments accept expressions, even 'r' ones: in 'r' args, we start by
; looking if the arg starts with 'r' or 'R'. If yes, it's a simple 'rXX' value,
; if not, we try parsing it as an expression and validate that it falls in the
; correct 0-31 or 16-31 range
argSpecs:
.db 'R', 0 ; Rd(5)
.db 'R', 'R' ; Rd(5) + Rr(5)
.db 7, 0 ; k(7)
.db 'r', 8 ; Rd(4) + K(8)
.db 'R', 'b' ; Rd(5) + bit
.db 'b', 7 ; bit + k(7)
.db 'R', 'A' ; Rd(5) + A(6)
.db 'D', 0 ; K(12)
.db 'a', 'b' ; A(5) + bit
.db 'r', 0 ; Rd(4)
.db 'b', 0 ; bit
; Parse arguments from I/O according to specs in HL
; H for first spec, L for second spec
; Puts the results in HL
; First arg in H, second in L.
; This routine is not used in all cases, some ops don't fit this pattern well
; and thus parse their args themselves.
; Z for success.
_parseArgs:
; For the duration of the routine, argspec is in DE and final MSB is
; in BC. We place result in HL at the end.
push de
push bc
ld bc, 0
ex de, hl ; argspecs now in DE
call readWord
jr nz, .end
ld a, d
call .parse
jr nz, .end
ld b, a
ld a, e
or a
jr z, .end ; no arg
call readComma
jr nz, .end
call readWord
jr nz, .end
ld a, e
call .parse
jr nz, .end
; we're done with (HL) now
ld c, a
cp a ; ensure Z
.end:
ld h, b
ld l, c
pop bc
pop de
ret
; Parse a single arg specified in A and returns its value in A
; Z for success
.parse:
cp 'R'
jr z, _readR5
cp 'r'
jr z, _readR4
cp 'b'
jr z, _readBit
cp 'A'
jr z, _readA6
cp 'a'
jr z, _readA5
cp 7
jr z, _readk7
cp 8
jr z, _readK8
cp 'D'
jr z, _readDouble
cp 'z'
jp z, _readz
ret ; something's wrong
_readBit:
ld a, 7
jp _readExpr
_readA6:
ld a, 0x3f
jp _readExpr
_readA5:
ld a, 0x1f
jp _readExpr
_readK8:
ld a, 0xff
jp _readExpr
_readDouble:
push de
call parseExpr
jr nz, .end
ld b, d
ld c, e
; BC is already set. For good measure, let's set A to BC's MSB
ld a, b
.end:
pop de
ret
_readk7:
push hl
push de
call parseExpr
jr nz, .end
; If we're in first pass, stop now. The value of HL doesn't matter and
; truncation checks might falsely fail.
call zasmIsFirstPass
jr z, .end
; DE contains an absolute value. Turn this into a -64/+63 relative
; value by subtracting PC from it. However, before we do that, let's
; add 0x7f to it, which we'll remove later. This will simplify bounds
; checks. (we use 7f instead of 3f because we deal in bytes here, not
; in words)
ld hl, 0x7f
add hl, de ; Carry cleared
ex de, hl
call zasmGetPC ; --> HL
; The relative value is actually not relative to current PC, but to
; PC after the execution of this branching op. Increase HL by 2.
inc hl \ inc hl
ex de, hl
sbc hl, de
jr c, .err ; Carry? error
ld de, 0x7f
sbc hl, de
; We're within bounds! However, our value in L is the number of
; relative *bytes*.
ld a, l
cp a ; ensure Z
.end:
pop de
pop hl
ret
.err:
call unsetZ
jr .end
_readR4:
call _readR5
ret nz
; has to be in the 16-31 range
sub 0x10
jp c, unsetZ
cp a ; ensure Z
ret
; read a rXX argument and return register number in A.
; Set Z for success.
_readR5:
push de
ld a, (hl)
call upcase
cp 'X'
jr z, .rdXYZ
cp 'Y'
jr z, .rdXYZ
cp 'Z'
jr z, .rdXYZ
cp 'R'
jr nz, .end ; not a register
inc hl
call parseDecimal
jr nz, .end
ld a, 31
call _DE2A
.end:
pop de
ret
.rdXYZ:
; First, let's get a base value, that is, (A-'X'+26)*2, because XL, our
; lowest register, is equivalent to r26.
sub 'X'
rla ; no carry from sub
add a, 26
ld d, a ; store that
inc hl
ld a, (hl)
call upcase
cp 'H'
jr nz, .skip1
; second char is 'H'? our value is +1
inc d
jr .skip2
.skip1:
cp 'L'
jr nz, .end ; not L either? then it's not good
.skip2:
; Good, we have our final value in D and we're almost sure it's a valid
; register. Our only check left is that the 3rd char is a null.
inc hl
ld a, (hl)
or a
jr nz, .end
; we're good
ld a, d
jr .end
; Put DE's LSB into A and, additionally, ensure that the new value is <=
; than what was previously in A.
; Z for success.
_DE2A:
cp e
jp c, unsetZ ; A < E
ld a, d
or a
ret nz ; should be zero
ld a, e
; Z set from "or a"
ret
; Read expr and return success only if result in under number given in A
; Z for success
_readExpr:
push de
push bc
ld b, a
call parseExpr
jr nz, .end
ld a, b
call _DE2A
jr nz, .end
or c
ld c, a
cp a ; ensure Z
.end:
pop bc
pop de
ret
; Parse one of the following: X, Y, Z, X+, Y+, Z+, -X, -Y, -Z.
; For each of those values, return a 5-bit value than can then be interleaved
; with LD or ST upcodes.
_readz:
call strlen
cp 3
jp nc, unsetZ ; string too long
; Let's load first char in A and second in A'. This will free HL
ld a, (hl)
ex af, af'
inc hl
ld a, (hl) ; Good, HL is now free
ld hl, .tblStraight
or a
jr z, .parseXYZ ; Second char null? We have a single char
; Maybe +
cp '+'
jr nz, .skip
; We have a +
ld hl, .tblInc
jr .parseXYZ
.skip:
; Maybe a -
ex af, af'
cp '-'
ret nz ; we have nothing
; We have a -
ld hl, .tblDec
; continue to .parseXYZ
.parseXYZ:
; We have X, Y or Z in A'
ex af, af'
call upcase
; Now, let's place HL
cp 'X'
jr z, .fetch
inc hl
cp 'Y'
jr z, .fetch
inc hl
cp 'Z'
ret nz ; error
.fetch:
ld a, (hl)
; Z already set from earlier cp
ret
.tblStraight:
.db 0b11100 ; X
.db 0b01000 ; Y
.db 0b00000 ; Z
.tblInc:
.db 0b11101 ; X+
.db 0b11001 ; Y+
.db 0b10001 ; Z+
.tblDec:
.db 0b11110 ; -X
.db 0b11010 ; -Y
.db 0b10010 ; -Z
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