236 lines
3.9 KiB
ArmAsm
236 lines
3.9 KiB
ArmAsm
; fast seek/multi-read
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; copyright (c) Peter Ferrie 2015-16
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sectors = 12 ; user-defined
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firsttrk = 1 ; user-defined, first track to read
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firstsec = 0 ; user-defined, first sector to read
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address = $12 ; user-defined
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entry = $1200 ; user-defined
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version = 1
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;memory usage:
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;256 bytes ($200-2ff) static table
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grouped = $200
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; stay aware from interrupt vectors at $3fe !!!
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;106 bytes ($300-369) static table
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preshift = $300
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zvalue = $fd ; only during init
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znibble = $fe ; only during init
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zmask = $ff ; only during init
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; $26/$27 sector read location (ROM)
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; $3D sector number (ROM)
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; at entry (at least on AppleWin) A=1, X=60 (slot<<4), Y=0
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; qkumba says cffa cards leave Y at $10
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; 26/27 = 00/09
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; 3D = 1
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; For Disk II booting, the firmware loads track0/sector0
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; to $800 and then jumps to $801
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.org $800
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.byte 1 ; number of sectors for ROM to load
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boot_entry:
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; this code loads two sectors up to $10/$11
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lsr ; check sector number
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tay
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adc #$0f
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sta $27 ; set or update address as needed
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cmp #$12
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; 10 11 12 (1 1 1)
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; be, bf, c0 (1011 1011 1100)
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; so if hit $c000 we are done
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beq done_load_2 ; branch if loaded 2
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inc $3d ; increment sector (faster to find)
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; call to the read routine in proper slot
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; using rts to jump indirect to
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; $CX5C
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; this routine reads sector in $3D on track in $41
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; to address in $26/$27
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; when it's done it jumps back to $801
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txa ; x is slot# << 4
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lsr
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lsr
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lsr
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lsr
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ora #$c0 ; slot to PROM base
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pha
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lda #$5b ;read-1
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pha
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rts
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done_load_2:
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; patch self modifying code for Q6L read
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txa
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ora #$8c ; slot to Q6L
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; Q6L?
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; if slot 6, after this A is $EC
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patch_loop:
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iny
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ldx patchtbl-3, Y
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sta code_begin, X ; replace placeholders with Q6L
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; BE02 = EC? lda c0ec
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; so sets to c08c (Q6L)
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bne patch_loop
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; patch self-modifying code for turning motor off
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and #$f8 ; MOTOROFF (c088) -> c0e8
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sta slotpatch7+1
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; patch self-modifying code for turning motor on
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clc
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adc #1 ; MOTOROFF (c088) -> c0e9
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sta slotpatch9+1
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; patch self-modifying code for phase off
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eor #9 ; PHASEOFF (c080)
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sta slotpatch8+1
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ldx #$3f
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stx zmask
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inx
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ldy #$7f
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bne skip_ahead ; branch always
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; pad with zeros until $839
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; $839 is the entry point
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; adjusts address at $8FE to be entry point
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; jumps to boot 2
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;.res $839-*
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; lda #>(entry-1)
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; pha
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; lda #<(entry-1)
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; pha
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; jsr preread
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; jmp $1000 ; stage2 entry point
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patchtbl:
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.byte <(slotpatch1+1), <(slotpatch2+1), <(slotpatch3+1)
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.byte <(slotpatch4+1), <(slotpatch5+1), <(slotpatch6+1)
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indextbl: ;the 0 also terminates the patchtbl list!
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.byte 0, 2, 1, 3
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;construct denibbilisation table
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;pre-shifted for interleave read
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skip_ahead:
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loopaa:
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sty znibble
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tya
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asl
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bit znibble
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beq loopz
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ora znibble
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eor #$ff
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and #$7e
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loopa:
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bcs loopz
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lsr
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bne loopa
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dex
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txa
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asl
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asl
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sta preshift-$16, Y
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loopz:
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dey
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bne loopaa
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;construct 2-bit group table
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sty zvalue
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loopbb:
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lsr zmask
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lsr zmask
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loopb:
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lda indextbl, X
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sta grouped, Y
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inc zvalue
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lda zvalue
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and zmask
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bne loopy
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inx
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txa
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and #3
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tax
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loopy:
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iny
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iny
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iny
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iny
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cpy #3
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bcs loopb
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iny
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cpy #3
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bcc loopbb
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lda #>(entry-1)
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pha
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lda #<(entry-1)
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pha
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jsr preread
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; seek backward support
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; sty startsec+1
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; sta tmpadr+1
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; stx total+1
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jmp seekread
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preread:
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;copy post-read if necessary
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;push post-read address here
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; pla
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; tax
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; pla
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; tay
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; lda #>(postread-1)
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; pha
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; lda #<(postread-1)
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; pha
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; tya
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; pha
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; txa
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; pha
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lda #<(firsttrk*2)
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sta phase+1
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ldx #sectors
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lda #address
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ldy #firstsec
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rts
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end_code:
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.res $8fe-*
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; traditionally, entry point to jump to at end of loading
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; $1000 in this case
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;*=$8fe
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.byte $10, $00
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.include "qboot_stage2.s"
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