/
ChSubs.asm
114 lines (102 loc) · 2.29 KB
/
ChSubs.asm
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BANKATMEMORY = $C000 ; where the bank memory is loaded
BANKVALUE = $5b5c ; the last value of bank selected
BANKPORT = $7FFD
;=========================================================
; To switch bank and do something, then return
; A-bank to 1..7, 0=default (2,5 are screen banks)
; HL-address of call-back sub to call
; (data reading when switched)
;
; Stack pointer should be set before 0xC000.
; Memory 0xC000-0xFFFF will contain bank data.
; Read data in sub, then restore bank.
; Do not call inside again, then create other.
;
; Sample:
; ld a,1
; ld hl,myproc_data_read_at_C000
; call BankCall
; ld a,2
; ld hl,myproc_data_read_at_C000
; call BankCall
; ...
;myproc_data_read_at_C000:
; ...
; ret
BankCall:
ld (BankClb),hl ; Save to memory
ld (BankStackSave),sp ; Save stack pointer
; ld sp, $BFFF ; Set stack before bank memory
push af
ld a,(BANKVALUE)
ld (BankValSave),a
pop af
call SETBANK ; set new bank
ld hl,BankRst
push hl ; push return address
ld hl,(BankClb)
jp (hl) ; call my callback sub
BankRst:
ld a,(BankValSave)
call SETBANK ; restore bank
ld sp,(BankStackSave) ; restore stack pointer
ret
BankClb:
.word 0 ; subroutine to call
BankStackSave:
.word 0 ; to save stack pointer
BankValSave:
.byte 0 ; to save bank selected
; This sets bank, A=bank 0..7
SETBANK:
di ; disable the interrupts.
push bc ; Remember BC.
ld bc, BANKPORT
or $10 ; Install ROM 48.
ld (BANKVALUE),a ; Change lane. BANK
out (c), a ; Output to port $7FFD values
pop bc
ei ; Enable interrupts.
ret
;=========================================================
; RANDOMIZER
; Sets A and returns value
;
Random0:
push bc
ld b,a
ld a,(Rnd0)
adc a,b
ld b,a
ld a,(RndI)
inc a
ld (RndI),a
adc a,b
rlc a
ld (Rnd0),a
pop bc
ret
Rnd0: .byte 0
RndI: .byte 0
Random1:
push bc
ld b,a
ld a,(Rnd1)
add b
rlc a
xor $ff
rlc a
ld (Rnd1),a
pop bc
ret
Rnd1: .byte 0
Random2:
push bc
ld b,a
ld a,(RndA)
inc a
ld (RndA),a
add b
pop bc
ret
RndA: .byte 0