dos33fsprogs/games/lemm/pt3_lib_mockingboard_detect.s
2022-03-05 23:25:44 -05:00

223 lines
5.3 KiB
ArmAsm

;===================================================================
; code to detect mockingboard
;===================================================================
; this isn't always easy
; my inclination is to just assume slot #4 but that isn't always realistic
; code below based on "hw.mockingboard.a" from "Total Replay"
;license:MIT
; By Andrew Roughan
; in the style of 4am for Total Replay
;
; Mockingboard support functions
;
;------------------------------------------------------------------------------
; HasMockingboard
; detect Mockingboard card by searching for 6522 timers across all slots
; access 6522 timers with deterministic cycle counts
;
; based on prior art in Mockingboard Developers Toolkit
; with optimisation from deater/french touch
; also takes into account FastChip //e clock difference
;
; in: none
; accelerators should be off
; out: C set if Mockingboard found in any slot
; if card was found, X = #$Cn where n is the slot number of the card
; C clear if no Mockingboard found
; other flags clobbered
; A/Y clobbered
;------------------------------------------------------------------------------
mockingboard_detect:
; activate Mockingboard IIc
; + the Mockingboard has to take over Slot#4 (IIc has no slots)
; in theory any write to the firmware area in $C400 will
; activate it, but that might not be fast enough when detecting
; so writing $FF to $C403/$C404 is official way to enable
; + Note this disables permanently the mouse firmware in $C400
; so "normal" interrupts are broken :( The hack to fix things
; is to switch in RAM for $F000 and just replace the IRQ
; vectors at $FFFE/$FFFF instead of $3FE/$3FF but that makes
; it difficult if you actually wanted to use any
; Applesoft/Monitor ROM routines
.ifdef PT3_ENABLE_APPLE_IIC
lda APPLEII_MODEL
cmp #'C'
bne not_iic
lda #$ff
; don't bother patching these, IIc mockingboard always slot 4
sta MOCK_6522_DDRA1 ; $C403
sta MOCK_6522_T1CL ; $C404
.endif
not_iic:
lda #$00
sta MB_ADDR_L
ldx #$C7 ; start at slot #7
mb_slot_loop:
stx MB_ADDR_H
ldy #$04 ; 6522 #1 $Cx04
jsr mb_timer_check
bne mb_next_slot
ldy #$84 ; 6522 #2 $Cx84
jsr mb_timer_check
bne mb_next_slot
mb_found:
sec ; found
rts
mb_next_slot:
dex
cpx #$C0
bne mb_slot_loop
clc ; not found
rts
mb_timer_check:
lda (MB_ADDR_L),Y ; read 6522 timer low byte
sta MB_VALUE
lda (MB_ADDR_L),Y ; second time
sec
sbc MB_VALUE
cmp #$F8 ; looking for (-)8 cycles between reads
beq mb_timer_check_done
cmp #$F7 ; FastChip //e clock is different
mb_timer_check_done:
rts
.if 0
;=======================================
; Detect a Mockingboard card
;=======================================
; Based on code from the French Touch "Pure Noise" Demo
; Attempts to time an instruction sequence with a 6522
;
; If found, puts in bMB
; MB_ADDRL:MB_ADDRH has address of Mockingboard
; returns X=0 if not found, X=1 if found
mockingboard_detect:
lda #0
sta MB_ADDRL
mb_detect_loop: ; self-modifying
lda #$07 ; we start in slot 7 ($C7) and go down to 0 ($C0)
ora #$C0 ; make it start with C
sta MB_ADDRH
ldy #04 ; $CX04
ldx #02 ; 2 tries?
mb_check_cycle_loop:
lda (MB_ADDRL),Y ; timer 6522 (Low Order Counter)
; count down
sta PT3_TEMP ; 3 cycles
lda (MB_ADDRL),Y ; + 5 cycles = 8 cycles
; between the two accesses to the timer
sec
sbc PT3_TEMP ; subtract to see if we had 8 cycles
cmp #$f8 ; -8
bne mb_not_in_this_slot
dex ; decrement, try one more time
bne mb_check_cycle_loop ; loop detection
inx ; Mockingboard found (X=1)
done_mb_detect:
;stx bMB ; store result to bMB
rts ; return
mb_not_in_this_slot:
dec mb_detect_loop+1 ; decrement the "slot" (self_modify)
bne mb_detect_loop ; loop down to one
ldx #00
beq done_mb_detect
;alternative MB detection from Nox Archaist
; lda #$04
; sta MB_ADDRL
; ldx #$c7
;
;find_mb:
; stx MB_ADDRH
;
; ;detect sound I
;
; sec
; ldy #$00
; lda (MB_ADDRL), y
; sbc (MB_ADDRL), y
; cmp #$05
; beq found_mb
; dex
; cpx #$c0
; bne find_mb
; ldx #$00 ;no mockingboard found
; rts
;
;found_mb:
; ldx #$01 ;mockingboard found
; rts
;
; ;optionally detect sound II
;
; sec
; ldy #$80
; lda (MB_ADDRL), y
; sbc (MB_ADDRL), y
; cmp #$05
; beq found_mb
;=======================================
; Detect a Mockingboard card in Slot4
;=======================================
; Based on code from the French Touch "Pure Noise" Demo
; Attempts to time an instruction sequence with a 6522
;
; MB_ADDRL:MB_ADDRH has address of Mockingboard
; returns X=0 if not found, X=1 if found
mockingboard_detect_slot4:
lda #0
sta MB_ADDRL
mb4_detect_loop: ; self-modifying
lda #$04 ; we're only looking in Slot 4
ora #$C0 ; make it start with C
sta MB_ADDRH
ldy #04 ; $CX04
ldx #02 ; 2 tries?
mb4_check_cycle_loop:
lda (MB_ADDRL),Y ; timer 6522 (Low Order Counter)
; count down
sta PT3_TEMP ; 3 cycles
lda (MB_ADDRL),Y ; + 5 cycles = 8 cycles
; between the two accesses to the timer
sec
sbc PT3_TEMP ; subtract to see if we had 8 cycles
cmp #$f8 ; -8
bne mb4_not_in_this_slot
dex ; decrement, try one more time
bne mb4_check_cycle_loop ; loop detection
inx ; Mockingboard found (X=1)
done_mb4_detect:
rts ; return
mb4_not_in_this_slot:
ldx #00
beq done_mb4_detect
.endif