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195 lines
3.9 KiB
ArmAsm
195 lines
3.9 KiB
ArmAsm
;
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; Karri Kaksonen, 2011
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;
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; This bootloader creates a signed binary so that the Lynx will accept it.
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;
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.include "lynx.inc"
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.include "extzp.inc"
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.import __BLOCKSIZE__
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.export __BOOTLDR__: absolute = 1
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; ------------------------------------------------------------------------
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; Bootloader
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.segment "BOOTLDR"
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;**********************************
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; Here is the bootloader in plaintext
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; The idea is to make the smalles possible encrypted loader as decryption
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; is very slow. The minimum size is 49 bytes plus a zero byte.
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;**********************************
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; EXE = $f000
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;
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; .org $0200
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;
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; ; 1. force Mikey to be in memory
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; stz MAPCTL
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;
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; ; 3. set ComLynx to open collector
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; lda #4 ; a = 00000100
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; sta SERCTL ; set the ComLynx to open collector
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;
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; ; 4. make sure the ROM is powered on
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; lda #8 ; a = 00001000
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; sta IODAT ; set the ROM power to on
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;
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; ; 5. read in secondary exe + 8 bytes from the cart and store it in $f000
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; ldx #0 ; x = 0
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; ldy #$AB ; y = secondary loader size (171 bytes)
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;rloop1: lda RCART0 ; read a byte from the cart
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; sta EXE,X ; EXE[X] = a
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; inx ; x++
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; dey ; y--
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; bne rloop1 ; loops until y wraps
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;
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; ; 6. jump to secondary loader
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; jmp EXE ; run the secondary loader
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;
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; .reloc
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;**********************************
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; After compilation, encryption and obfuscation it turns into this.
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;**********************************
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.byte $ff, $dc, $e3, $bd, $bc, $7f, $f8, $94
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.byte $b7, $dd, $68, $bb, $da, $5b, $50, $5c
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.byte $ea, $9f, $2b, $df, $96, $80, $3f, $7e
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.byte $ef, $15, $81, $ae, $ad, $e4, $6e, $b3
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.byte $46, $d7, $72, $58, $f7, $76, $8a, $4a
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.byte $c7, $99, $bd, $ff, $02, $3e, $5b, $3f
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.byte $0c, $49, $1b, $22
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;**********************************
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; Now we have the secondary loader
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;**********************************
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.org $f000
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; 1. Read in the 1st File-entry (main exe) in FileEntry
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ldx #$00
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ldy #8
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rloop: lda RCART0 ; read a byte from the cart
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sta _FileEntry,X ; EXE[X] = a
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inx
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dey
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bne rloop
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; 2. Set the block hardware to the main exe start
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lda _FileStartBlock
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sta _FileCurrBlock
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jsr seclynxblock
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; 3. Skip over the block offset
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lda _FileBlockOffset
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ldx _FileBlockOffset+1
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phx ; The BLL kit uses negative offsets
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plx ; while the basic Lynx uses positive
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bmi @1 ; Make all offsets negative
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eor #$FF
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pha
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txa
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eor #$FF
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bra @2
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@1: pha
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txa
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@2: tay
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plx
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jsr seclynxskip0
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; 4. Read in the main exe to RAM
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lda _FileDestAddr
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ldx _FileDestAddr+1
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sta _FileDestPtr
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stx _FileDestPtr+1
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lda _FileFileLen
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ldx _FileFileLen+1
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phx ; The BLL kit uses negative counts
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plx ; while the basic Lynx uses positive
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bmi @3 ; make all counts negative
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eor #$FF
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pha
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txa
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eor #$FF
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bra @4
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@3: pha
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txa
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@4: tay
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plx
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jsr seclynxread0
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; 5. Jump to start of the main exe code
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jmp (_FileDestAddr)
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;**********************************
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; Skip bytes on bank 0
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; X:Y count (EOR $FFFF)
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;**********************************
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seclynxskip0:
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inx
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bne @0
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iny
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beq exit
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@0: jsr secreadbyte0
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bra seclynxskip0
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;**********************************
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; Read bytes from bank 0
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; X:Y count (EOR $ffff)
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;**********************************
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seclynxread0:
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inx
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bne @1
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iny
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beq exit
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@1: jsr secreadbyte0
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sta (_FileDestPtr)
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inc _FileDestPtr
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bne seclynxread0
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inc _FileDestPtr+1
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bra seclynxread0
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;**********************************
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; Read one byte from cartridge
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;**********************************
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secreadbyte0:
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lda RCART0
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inc _FileBlockByte
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bne exit
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inc _FileBlockByte+1
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bne exit
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;**********************************
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; Select a block
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;**********************************
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seclynxblock:
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pha
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phx
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phy
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lda __iodat
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and #$fc
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tay
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ora #2
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tax
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lda _FileCurrBlock
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inc _FileCurrBlock
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sec
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bra @2
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@0: bcc @1
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stx IODAT
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clc
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@1: inx
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stx SYSCTL1
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dex
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@2: stx SYSCTL1
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rol
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sty IODAT
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bne @0
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lda __iodat
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sta IODAT
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stz _FileBlockByte
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lda #<($100-(>__BLOCKSIZE__))
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sta _FileBlockByte+1
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ply
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plx
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pla
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exit: rts
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.reloc
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