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cc65/libsrc/lynx/bootldr.s
2022-04-16 18:16:14 +02:00

196 lines
5.1 KiB
ArmAsm

;
; Karri Kaksonen, 2011
;
; This bootloader creates a signed binary so that the Lynx will accept it.
;
.include "lynx.inc"
.include "extzp.inc"
.import __BANK0BLOCKSIZE__
.export __BOOTLDR__: absolute = 1
; ------------------------------------------------------------------------
; Bootloader
.segment "BOOTLDR"
;**********************************
; Here is the bootloader in plaintext
; The idea is to make the smalles possible encrypted loader as decryption
; is very slow. The minimum size is 49 bytes plus a zero byte.
;**********************************
; EXE = $fb68
;
; .org $0200
;
; ; 1. force Mikey to be in memory
; 9C F9 FF stz MAPCTL
;
; ; 2. clear palette
; A0 1F ldy #31
; A9 00 lda #0
; 99 A0 FD nextc: sta GCOLMAP, y
; 88 dey
; 10 FA bpl nextc
;
; ; 3. set ComLynx to open collector
; A9 04 lda #4 ; a = 00000100
; 8D 8C FD sta SERCTL ; set the ComLynx to open collector
;
; ; 4. set AUDIN to output
; A9 1A lda #$1a ; audin = out, rest = out,
; ; noexp = in, cart addr = out, ext pwd = in
; 8D 8A FD sta IODIR
;
; ; 5. set AUDIN to LOW
; A9 0B lda #$0B ; Set AUDIN low
; 85 1A sta $1a ; Save local copy to ZP
; 8D 8B FD sta IODAT
;
; ; 6. read in secondary exe + 8 bytes from the cart
; ; and store it in $f000
; A2 00 ldx #0 ; x = 0
; A0 97 ldy #$97 ; y = secondary loader size (151 bytes)
; AD B2 FC rloop1: lda RCART0 ; read a byte from the cart
; 9D 68 FB sta EXE,X ; EXE[X] = a
; E8 inx ; x++
; 88 dey ; y--
; D0 F6 bne rloop1 ; loops until y wraps
;
; ; 7. jump to secondary loader
; 4C 68 FB jmp EXE
; 00 00 00 00 ; spares
; 00 ; End of encrypted header mark
;
; .reloc
;**********************************
; After compilation, encryption and obfuscation it turns into this.
;**********************************
.byte $ff, $b6, $bb, $82, $d5, $9f, $48, $cf
.byte $23, $37, $8e, $07, $38, $f5, $b6, $30
.byte $d6, $2f, $12, $29, $9f, $43, $5b, $2e
.byte $f5, $66, $5c, $db, $93, $1a, $78, $55
.byte $5e, $c9, $0d, $72, $1b, $e9, $d8, $4d
.byte $2f, $e4, $95, $c0, $4f, $7f, $1b, $66
.byte $8b, $a7, $fc, $21
;**********************************
; Now we have the secondary loader
;**********************************
.org $fb68
; 1. Read in the 1st File-entry (main exe) in FileEntry
ldx #$00
ldy #8
rloop: lda RCART0 ; read a byte from the cart
sta _FileEntry,X ; EXE[X] = a
inx
dey
bne rloop
; 2. Set the block hardware to the main exe start
lda _FileStartBlock
sta _FileCurrBlock
jsr seclynxblock
; 3. Skip over the block offset
lda _FileBlockOffset+1
eor #$FF
tay
lda _FileBlockOffset
eor #$FF
tax
jsr seclynxskip0
; 4. Read in the main exe to RAM
lda _FileDestAddr
ldx _FileDestAddr+1
sta _FileDestPtr
stx _FileDestPtr+1
lda _FileFileLen+1
eor #$FF
tay
lda _FileFileLen
eor #$FF
tax
jsr seclynxread0
; 5. Jump to start of the main exe code
jmp (_FileDestAddr)
;**********************************
; Skip bytes on bank 0
; X:Y count (EOR $FFFF)
;**********************************
seclynxskip0:
inx
bne @0
iny
beq exit
@0: jsr secreadbyte0
bra seclynxskip0
;**********************************
; Read bytes from bank 0
; X:Y count (EOR $ffff)
;**********************************
seclynxread0:
inx
bne @1
iny
beq exit
@1: jsr secreadbyte0
sta (_FileDestPtr)
inc _FileDestPtr
bne seclynxread0
inc _FileDestPtr+1
bra seclynxread0
;**********************************
; Read one byte from cartridge
;**********************************
secreadbyte0:
lda RCART0
inc _FileBlockByte
bne exit
inc _FileBlockByte+1
bne exit
;**********************************
; Select a block
;**********************************
seclynxblock:
pha
phx
phy
lda __iodat
and #$fc
tay
ora #2
tax
lda _FileCurrBlock
inc _FileCurrBlock
sec
bra @2
@0: bcc @1
stx IODAT
clc
@1: inx
stx SYSCTL1
dex
@2: stx SYSCTL1
rol
sty IODAT
bne @0
lda __iodat
sta IODAT
stz _FileBlockByte
lda #<($100-(>__BANK0BLOCKSIZE__))
sta _FileBlockByte+1
ply
plx
pla
exit: rts
.reloc