mirror of
https://github.com/peterferrie/standard-delivery.git
synced 2025-01-20 02:30:49 +00:00
107 lines
3.1 KiB
ArmAsm
107 lines
3.1 KiB
ArmAsm
;license:BSD-3-Clause
|
|
;fast boot-loader in one sector
|
|
;copyright (c) Peter Ferrie 2016
|
|
;thanks to 4am for inspiration and testing
|
|
;assemble using ACME
|
|
!cpu 6502
|
|
!to "fstbt",plain
|
|
*=$800
|
|
|
|
enable_banked = 0 ;set to bank number (1 or 2) to enable reading into banked RAM
|
|
|
|
!byte 1
|
|
|
|
tay ;A is last read sector+1 on entry
|
|
!if enable_banked > 0 {
|
|
lda $C081 ;bank in ROM
|
|
}
|
|
|
|
;check array before checking sector number
|
|
;allows us to avoid a redundant seek if all slots are full in a track,
|
|
;and then the list ends
|
|
|
|
incindex
|
|
inc adrindex + 1 ;select next address
|
|
|
|
adrindex
|
|
lda adrtable - 1 ;15 entries in first row, 16 entries thereafter
|
|
cmp #$C0
|
|
beq jmpoep ;#$C0 means end of data
|
|
sta $27 ;set high part of address
|
|
lda #1 ;preload in case we are finished with the first round
|
|
|
|
;2, 4, 6, 8, $0A, $0C, $0E
|
|
;because PROM increments by one itself
|
|
;and is too slow to read sectors in purely incremental order
|
|
;so we offer every other sector for read candidates
|
|
|
|
iny
|
|
cpy #$10
|
|
bcc setsector ;cases 1-$0F
|
|
beq sector1 ;finished with $0E
|
|
;next should be 1 for 1, 3, 5, 7... sequence
|
|
|
|
;finished with $0F, now we are $11, so 16 sectors done
|
|
|
|
jsr seek ;returns A=0
|
|
|
|
;back to 0
|
|
|
|
sector1
|
|
tay
|
|
|
|
setsector
|
|
sty $3D ;set sector
|
|
iny ;prepare to be next sector in case of unallocated sector
|
|
lda $27
|
|
beq incindex ;empty slot, back to the top
|
|
|
|
;convert slot to PROM address
|
|
|
|
txa
|
|
jsr $F87B ;4xlsr
|
|
ora #$C0
|
|
pha
|
|
lda #$5B ;read-1
|
|
pha
|
|
|
|
!if enable_banked > 0 {
|
|
writeenable
|
|
lda $C093-(enable_banked*8)
|
|
lda $C093-(enable_banked*8)
|
|
;write-enable RAM and bank it in so read can decode
|
|
}
|
|
rts ;return to PROM
|
|
|
|
seek
|
|
inc $41 ;next track
|
|
asl $40 ;carry clear, phase off
|
|
jsr seek1 ;returns carry set, not useful
|
|
clc ;carry clear, phase off
|
|
|
|
seek1
|
|
jsr delay ;returns with carry set, phase on
|
|
inc $40 ;next phase
|
|
|
|
delay
|
|
lda $40
|
|
and #3
|
|
rol
|
|
ora $2B ;merge in slot
|
|
tay
|
|
lda $C080, y
|
|
lda #$30
|
|
jmp $FCA8 ;common delay for all phases
|
|
|
|
jmpoep
|
|
!if enable_banked > 0 {
|
|
jsr writeenable ;bank in our RAM, write-enabled
|
|
}
|
|
jmp $1234 ;arbitrary entry-point to use after read completes
|
|
;set to the value that you need
|
|
|
|
adrtable
|
|
;15 slots for track 0 (track 0 sector 0 is not addressable)
|
|
;16 slots for all other tracks, fill with addresses, 0 to skip any sector
|
|
!byte $C0 ;end of list
|