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added config switch to disable decimal mode tests
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decimal mode tests can be disabled for the ADC & SBC instructions or
also including the decimal mode bit of the processor status register.
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@Klaus2m5
Klaus2m5 committed Oct 21, 2015
1 parent d0cd6d0 commit 54768c6
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; Verify decimal mode behavior
; Written by Bruce Clark. This code is public domain.
; see http://www.6502.org/tutorials/decimal_mode.html
;
; Returns:
; ERROR = 0 if the test passed
; ERROR = 1 if the test failed
; modify the code at the DONE label for desired program end
;
; This routine requires 17 bytes of RAM -- 1 byte each for:
; AR, CF, DA, DNVZC, ERROR, HA, HNVZC, N1, N1H, N1L, N2, N2L, NF, VF, and ZF
; and 2 bytes for N2H
;
; Variables:
; N1 and N2 are the two numbers to be added or subtracted
; N1H, N1L, N2H, and N2L are the upper 4 bits and lower 4 bits of N1 and N2
; DA and DNVZC are the actual accumulator and flag results in decimal mode
; HA and HNVZC are the accumulator and flag results when N1 and N2 are
; added or subtracted using binary arithmetic
; AR, NF, VF, ZF, and CF are the predicted decimal mode accumulator and
; flag results, calculated using binary arithmetic
;
; This program takes approximately 1 minute at 1 MHz (a few seconds more on
; a 65C02 than a 6502 or 65816)
;

; Configuration:
cputype = 0 ; 0 = 6502, 1 = 65C02, 2 = 65C816
vld_bcd = 0 ; 0 = allow invalid bcd, 1 = valid bcd only
chk_a = 1 ; check accumulator
chk_n = 0 ; check sign (negative) flag
chk_v = 0 ; check overflow flag
chk_z = 0 ; check zero flag
chk_c = 1 ; check carry flag

end_of_test macro
db $db ;execute 65C02 stop instruction
endm

bss
org 0
; operands - register Y = carry in
N1 ds 1
N2 ds 1
; binary result
HA ds 1
HNVZC ds 1
;04
; decimal result
DA ds 1
DNVZC ds 1
; predicted results
AR ds 1
NF ds 1
;08
VF ds 1
ZF ds 1
CF ds 1
ERROR ds 1
;0C
; workspace
N1L ds 1
N1H ds 1
N2L ds 1
N2H ds 2

code
org $200
TEST ldy #1 ; initialize Y (used to loop through carry flag values)
sty ERROR ; store 1 in ERROR until the test passes
lda #0 ; initialize N1 and N2
sta N1
sta N2
LOOP1 lda N2 ; N2L = N2 & $0F
and #$0F ; [1] see text
if vld_bcd = 1
cmp #$0a
bcs NEXT2
endif
sta N2L
lda N2 ; N2H = N2 & $F0
and #$F0 ; [2] see text
if vld_bcd = 1
cmp #$a0
bcs NEXT2
endif
sta N2H
ora #$0F ; N2H+1 = (N2 & $F0) + $0F
sta N2H+1
LOOP2 lda N1 ; N1L = N1 & $0F
and #$0F ; [3] see text
if vld_bcd = 1
cmp #$0a
bcs NEXT1
endif
sta N1L
lda N1 ; N1H = N1 & $F0
and #$F0 ; [4] see text
if vld_bcd = 1
cmp #$a0
bcs NEXT1
endif
sta N1H
jsr ADD
jsr A6502
jsr COMPARE
bne DONE
jsr SUB
jsr S6502
jsr COMPARE
bne DONE
NEXT1 inc N1 ; [5] see text
bne LOOP2 ; loop through all 256 values of N1
NEXT2 inc N2 ; [6] see text
bne LOOP1 ; loop through all 256 values of N2
dey
bpl LOOP1 ; loop through both values of the carry flag
lda #0 ; test passed, so store 0 in ERROR
sta ERROR
DONE
end_of_test

; Calculate the actual decimal mode accumulator and flags, the accumulator
; and flag results when N1 is added to N2 using binary arithmetic, the
; predicted accumulator result, the predicted carry flag, and the predicted
; V flag
;
ADD sed ; decimal mode
cpy #1 ; set carry if Y = 1, clear carry if Y = 0
lda N1
adc N2
sta DA ; actual accumulator result in decimal mode
php
pla
sta DNVZC ; actual flags result in decimal mode
cld ; binary mode
cpy #1 ; set carry if Y = 1, clear carry if Y = 0
lda N1
adc N2
sta HA ; accumulator result of N1+N2 using binary arithmetic

php
pla
sta HNVZC ; flags result of N1+N2 using binary arithmetic
cpy #1
lda N1L
adc N2L
cmp #$0A
ldx #0
bcc A1
inx
adc #5 ; add 6 (carry is set)
and #$0F
sec
A1 ora N1H
;
; if N1L + N2L < $0A, then add N2 & $F0
; if N1L + N2L >= $0A, then add (N2 & $F0) + $0F + 1 (carry is set)
;
adc N2H,x
php
bcs A2
cmp #$A0
bcc A3
A2 adc #$5F ; add $60 (carry is set)
sec
A3 sta AR ; predicted accumulator result
php
pla
sta CF ; predicted carry result
pla
;
; note that all 8 bits of the P register are stored in VF
;
sta VF ; predicted V flags
rts

; Calculate the actual decimal mode accumulator and flags, and the
; accumulator and flag results when N2 is subtracted from N1 using binary
; arithmetic
;
SUB sed ; decimal mode
cpy #1 ; set carry if Y = 1, clear carry if Y = 0
lda N1
sbc N2
sta DA ; actual accumulator result in decimal mode
php
pla
sta DNVZC ; actual flags result in decimal mode
cld ; binary mode
cpy #1 ; set carry if Y = 1, clear carry if Y = 0
lda N1
sbc N2
sta HA ; accumulator result of N1-N2 using binary arithmetic

php
pla
sta HNVZC ; flags result of N1-N2 using binary arithmetic
rts

if cputype != 1
; Calculate the predicted SBC accumulator result for the 6502 and 65816
;
SUB1 cpy #1 ; set carry if Y = 1, clear carry if Y = 0
lda N1L
sbc N2L
ldx #0
bcs S11
inx
sbc #5 ; subtract 6 (carry is clear)
and #$0F
clc
S11 ora N1H
;
; if N1L - N2L >= 0, then subtract N2 & $F0
; if N1L - N2L < 0, then subtract (N2 & $F0) + $0F + 1 (carry is clear)
;
sbc N2H,x
bcs S12
sbc #$5F ; subtract $60 (carry is clear)
S12 sta AR
rts
endif

if cputype = 1
; Calculate the predicted SBC accumulator result for the 6502 and 65C02
;
SUB2 cpy #1 ; set carry if Y = 1, clear carry if Y = 0
lda N1L
sbc N2L
ldx #0
bcs S21
inx
and #$0F
clc
S21 ora N1H
;
; if N1L - N2L >= 0, then subtract N2 & $F0
; if N1L - N2L < 0, then subtract (N2 & $F0) + $0F + 1 (carry is clear)
;
sbc N2H,x
bcs S22
sbc #$5F ; subtract $60 (carry is clear)
S22 cpx #0
beq S23
sbc #6
S23 sta AR ; predicted accumulator result
rts
endif

; Compare accumulator actual results to predicted results
;
; Return:
; Z flag = 1 (BEQ branch) if same
; Z flag = 0 (BNE branch) if different
;
COMPARE
if chk_a = 1
lda DA
cmp AR
bne C1
endif
if chk_n = 1
lda DNVZC ; [7] see text
eor NF
and #$80 ; mask off N flag
bne C1
endif
if chk_v = 1
lda DNVZC ; [8] see text
eor VF
and #$40 ; mask off V flag
bne C1 ; [9] see text
endif
if chk_z = 1
lda DNVZC
eor ZF ; mask off Z flag
and #2
bne C1 ; [10] see text
endif
if chk_c = 1
lda DNVZC
eor CF
and #1 ; mask off C flag
endif
C1 rts

; These routines store the predicted values for ADC and SBC for the 6502,
; 65C02, and 65816 in AR, CF, NF, VF, and ZF

if cputype = 0

A6502 lda VF ; 6502
;
; since all 8 bits of the P register were stored in VF, bit 7 of VF contains
; the N flag for NF
;
sta NF
lda HNVZC
sta ZF
rts

S6502 jsr SUB1
lda HNVZC
sta NF
sta VF
sta ZF
sta CF
rts

endif
if cputype = 1

A6502 lda AR ; 65C02
php
pla
sta NF
sta ZF
rts

S6502 jsr SUB2
lda AR
php
pla
sta NF
sta ZF
lda HNVZC
sta VF
sta CF
rts

endif
if cputype = 2

A6502 lda AR ; 65C816
php
pla
sta NF
sta ZF
rts

S6502 jsr SUB1
lda AR
php
pla
sta NF
sta ZF
lda HNVZC
sta VF
sta CF
rts

endif

end TEST

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