RESTORE key now acts as very soft reset, and for startup
This reverts commit 69d9f49b5c.
This commit is contained in:
parent
24b2374d3e
commit
cf56f3c11c
2 changed files with 43 additions and 102 deletions
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@ -1,6 +1,6 @@
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;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
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.scope STARTUP
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.proc STARTUP
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;; Settings positions
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CR1 = $d011; Graphic settings
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VIC_bank_settings = $DD00 ; Vic position
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@ -69,8 +69,7 @@
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;; Disable maskeble interups (not all)
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SEI
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;; Set up bank switching.
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;; Disable BASIC and KERNAL(sic) ROM, keep I/O
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;; Disable BASIC ROM mohahaha
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;; https://www.c64-wiki.com/wiki/Bank_Switching
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LDA #%11111000
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AND $01
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@ -81,29 +80,36 @@
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;;Disable non maskable interupts
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;;https://codebase64.org/doku.php?id=base:nmi_lock_without_kernal
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;; write to $FFFA/$FFFB possible (and needed) if KERNAL ROM is disabled
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;; write to $FFFA/$FFFB possible (and needed) if BASIC ROM is disabled
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LDA #<NMI_routine
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STA $FFFA
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LDA #>NMI_routine
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STA $FFFB
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LDA #$00 ;; stop Timer A
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STA $DD0E
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STA $DD04 ;; set Timer A to 0, after starting
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STA $DD05 ;; NMI will occur immediately
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LDA #$81
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STA $DD0D ;; set Timer A as source for NMI
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LDA #$01
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STA $DD0E ;; start Timer A -> NMI
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;; from here on NMI is disabled
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;; Set up IRQ for userprog transfer timer
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LDA #<IRQ_routine
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STA $FFFE
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LDA #>IRQ_routine
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STA $FFFF
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LDA #%00101000 ;; stop Timer A
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STA $DD0E
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STA $DD04 ;; set Timer A to 0, after starting
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STA $DD05 ;; NMI will occur immediately
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LDA #$80
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STA $DD0D ;; set Timer A as source for NMI
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LDA #%00101000
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STA $DD0E ;; start Timer A -> NMI
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;; from here on NMI is disabled
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JMP mainsetup
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NMI_routine:
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RTI ;; exit interrupt not acknowledged
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.endscope
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BIT $DD0D
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LDA #%11111110
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STA $DD0D
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JMP STARTUP
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IRQ_routine:
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PHA
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BIT $DC0D
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LDA #$00
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STA $DC0D
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PLA
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RTI
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.endproc
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@ -1,6 +1,5 @@
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;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
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mainsetup:
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.scope mainsetup
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.proc mainsetup
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USERPROG = $C000
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.repeat 4, I
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ldy #$00
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@ -10,60 +9,20 @@ mainsetup:
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dey
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bne :-
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.endrep
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.endproc
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@waitstart: ;; Wait until joystick 2 has been pulled down to start the program
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dec $d020
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lda #%11111111
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sta $dc02
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lda #%00000000
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sta $dc03
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lda #%01111111
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sta $dc00
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lda $dc01
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eor #$ff
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beq @waitstart
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lda #%00000000
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sta $dc02
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endsetup:
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DOWNLOAD_TIMER = $FFFF
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mainstart:
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lda #$0d
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sta $d020
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;; Turn on CIA 1's Timer A as IRQ source Summary: Timer A counts down
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;; for 0xFFFF cycles. When it finishes, an IRQ is sent to the
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;; CPU. Once it's ready to receive it, the IRQ routine is called,
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;; which checks if a userprog download is beginning. If it is, we
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;; download and reset the unwind the stack. The transfer hardware has
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;; a certain delay between the transfer command being sent and the
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;; start of bits being sent. This duration must be some amount longer
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;; than the timer's duration to account for variable execution time of
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;; interrupt-free routines.
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sei ; let's be extra sure interrupts are disabled
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lda #<DOWNLOAD_TIMER
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sta $dc04 ; Timer A's counter low byte
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lda #>DOWNLOAD_TIMER
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sta $dc05 ; Likewise for high byte
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lda #%10000001 ; Send IRQ to CPU when Timer A is done
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sta $dc0d
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lda #%00011001 ; Start Timer A, one-shot mode, cycle counting mode
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sta $dc0e
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.scope mainloop
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ldx #$00
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stx FRAMECOUNT
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inx
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sta FIRSTTIME
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.endscope
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.proc mainloop
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ml:
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USERPROG = $C000
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RASTER = $D012
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@ -72,9 +31,19 @@ endsetup:
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ora $01
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sta $01
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cli
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jsr maybe_download_userprog
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beq @nochange
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ldx #$00
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stx FRAMECOUNT
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inx
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sta FIRSTTIME
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@nochange:
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jsr USERPROG
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;; Bank out character ROM, I/O in
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lda #%00000100
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ora $01
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sta $01
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@framewait:
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ldy RASTER
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cpy #$66
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@ -82,8 +51,8 @@ endsetup:
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inc FRAMECOUNT
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lda #$00
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sta FIRSTTIME
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jmp mainloop
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.endproc
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jmp ml
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.endscope
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.proc time ; user-procedure
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lda FRAMECOUNT
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@ -107,41 +76,7 @@ endsetup:
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rts
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.endproc
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.proc reset_userprog
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ldx #$00
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stx FRAMECOUNT
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inx
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sta FIRSTTIME
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.endproc
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FRAMECOUNT: .byte 0
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FIRSTTIME: .byte 1
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IRQ_routine:
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lda $dc0d ; Check CIA 1's status
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beq @somethingelse
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jsr maybe_download_userprog
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beq @done
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jsr reset_userprog
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;; Reconstruct the stack to exit to toplevel
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ldx #$00
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txs
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lda #<mainloop
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pha
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lda #>mainloop
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pha
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txa
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pha
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lda #%00011001 ; Start Timer A, one-shot mode, cycle counting
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sta $dc0e
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rti
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@somethingelse:
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;; TODO: Ack potential VIC-II IRQ
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@done:
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lda #%00011001 ; Start Timer A, one-shot mode, cycle counting
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sta $dc0e
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rti
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RESTORE_DEST: .word mainsetup
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