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180 lines
4.5 KiB
ArmAsm
180 lines
4.5 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 __BANK0BLOCKSIZE__
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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 = $fb68
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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 #$97 ; y = secondary loader size (151 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, $81, $ca, $33, $be, $80, $a2, $c4
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.byte $6d, $98, $fe, $8d, $bc, $66, $c0, $7a
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.byte $09, $50, $23, $28, $18, $c8, $06, $70
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.byte $58, $4f, $1b, $e1, $c7, $90, $08, $cd
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.byte $1a, $6e, $5a, $45, $32, $d7, $6d, $c6
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.byte $8a, $e5, $d8, $5c, $a0, $e8, $4f, $7a
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.byte $5f, $73, $8d, $22
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;**********************************
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; Now we have the secondary loader
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;**********************************
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.org $fb68
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; 1. Read in the 1st File-entry (main exe) in FileEntry
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ldx #$00
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ldy #8
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rloop: lda RCART0 ; read a byte from the cart
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sta _FileEntry,X ; EXE[X] = a
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inx
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dey
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bne rloop
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; 2. Set the block hardware to the main exe start
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lda _FileStartBlock
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sta _FileCurrBlock
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jsr seclynxblock
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; 3. Skip over the block offset
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lda _FileBlockOffset+1
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eor #$FF
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tay
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lda _FileBlockOffset
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eor #$FF
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tax
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jsr seclynxskip0
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; 4. Read in the main exe to RAM
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lda _FileDestAddr
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ldx _FileDestAddr+1
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sta _FileDestPtr
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stx _FileDestPtr+1
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lda _FileFileLen+1
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eor #$FF
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tay
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lda _FileFileLen
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eor #$FF
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tax
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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-(>__BANK0BLOCKSIZE__))
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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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