如何在汇编程序中反转秒表代码以进行倒计时？

Question

我在汇编器中为秒表写了这段代码。如果你按下button1，它将开始计数。如果您再次按同一按钮，它将暂停，再按一次将恢复秒表。按下数字2按钮可重置秒表。

这是相当长的一段时间，因为我是在PicoBlaze汇编器中编程，这是几年前的代码，因为我有几年没有编程，我忘记了很多。但现在我需要稍微修改一下，我需要你的帮助。

所以我现在想要的是有倒计时的功能。所以当我按下button1时，它会开始计数，再按一次就会暂停，再按一次就会恢复。但按下button2将开始倒计时，与暂停和恢复相同的按钮，并将重置从button2移动到新的button3。

有人能帮我吗？谢谢。

VHDL    "ROM_blank.vhd", "ProgMem.vhd", "ProgMem"
BUTTON      DSIN        $00
SWITCH      DSIN        $01
LED         DSOUT       $02
SEG0        DSOUT       $03
SEG1        DSOUT       $04
SEG2        DSOUT       $05
SEG3        DSOUT       $06

wait0 equ s0
wait1 equ s1
wait2 equ s2
cnt0 equ s3
cnt1 equ s4
cnt2 equ s5
cnt3 equ s6
state equ s7
segsel equ s8
temp equ sf

state_r0 equ 0
state_r1 equ 1
state_s0 equ 2
state_s1 equ 3

decoded_dp equ 254
decoded_0 equ 3
decoded_1 equ 159
decoded_2 equ 37
decoded_3 equ 13
decoded_4 equ 153
decoded_5 equ 73
decoded_6 equ 65
decoded_7 equ 27
decoded_8 equ 1
decoded_9 equ 25
decoded_A equ 5
decoded_B equ 193
decoded_C equ 229
decoded_D equ 133
decoded_E equ 97
decoded_F equ 113


init:
     load cnt0, 0
     load cnt1, 0
     load cnt2, 0
     load cnt3, 0
     load state, state_s0
start:

; read buttons
    in temp, BUTTON
; reset check
    and temp, 2
    jump z, startstop_check
    load cnt0, 0
    load cnt1, 0
    load cnt2, 0
    load cnt3, 0

startstop_check:
    in temp, BUTTON
    and temp, 1

; state machine
    comp state, state_r0
    jump z,run0
    comp state, state_r1
    jump z,run1
    comp state, state_s0
    jump z, stop0
    comp state, state_s1
    jump z, stop1
    load state, state_s0

stop0:
    comp temp, 1
    jump nz, fsm_end
    load state, state_r0
    jump fsm_end
run0:
    comp temp, 0
    jump nz, fsm_end
    load state, state_r1
    jump fsm_end
run1:
    comp temp, 1
    jump nz, fsm_end
    load state, state_s1
    jump fsm_end
stop1:
    comp temp, 0
    jump nz, fsm_end
    load state, state_s0

fsm_end:

;wait 0.01s     
    call waitfcn

    comp state, state_s0
    jump z, decode
    comp state, state_s1
    jump z, decode

    add cnt0, 1
    comp cnt0, 10
    jump nz, decode
    load cnt0, 0
    add cnt1, 1
    comp cnt1, 10
    jump nz, decode
    load cnt1, 0
    add cnt2, 1
    comp cnt2, 10
    jump nz, decode
    load cnt2, 0
    add cnt3, 1
    comp cnt3, 10
    jump nz, decode
    load cnt3, 0

decode:
;decode for output
    load temp, cnt0
    call decodefcn
    out temp, SEG0

    load temp, cnt1
    call decodefcn
    out temp, SEG1

    load temp, cnt2
    call decodefcn
;add decimal point
    and temp, 254
    out temp, SEG2

    load temp, cnt3
    call decodefcn
    out temp, SEG3

    jump start

decodefcn:
    comp temp, 0
    jump nz, dec1
    load temp, decoded_0
    ret
dec1:
    comp temp, 1
    jump nz, dec2
    load temp, decoded_1
    ret
dec2:
    comp temp, 2
    jump nz, dec3
    load temp, decoded_2
    ret
dec3:
    comp temp, 3
    jump nz, dec4
    load temp, decoded_3
    ret
dec4:
    comp temp, 4
    jump nz, dec5
    load temp, decoded_4
    ret
dec5:
    comp temp, 5
    jump nz, dec6
    load temp, decoded_5
    ret
dec6:
    comp temp, 6
    jump nz, dec7
    load temp, decoded_6
    ret
dec7:
    comp temp, 7
    jump nz, dec8
    load temp, decoded_7
    ret
dec8:
    comp temp, 8
    jump nz, dec9
    load temp, decoded_8
    ret
dec9:
    load temp, decoded_9
    ret

waitfcn:
    load wait2, 25
wt0:
    load wait1, 25
wt1 :   
    load wait0, 200
wt2 :
    sub wait0, 1
    jump nz, wt2
    sub wait1, 1
    jump nz, wt1
    sub wait2, 1
    jump nz, wt0
    ret
END

Answer 1

基本上可以通过添加状态和复制编辑第二个按钮的代码+将第二个按钮的内容移动到第三个按钮来完成。然后是将递增计数编辑为递减计数：

;wait 0.01s     
    call waitfcn

    comp state, state_s0
    jump z, decode
    comp state, state_s1
    jump z, decode

    sub  cnt0, 1
    comp cnt0, 255 ; -1
    jump nz, decode
    load cnt0, 9
    sub  cnt1, 1
    comp cnt1, 255
    ...