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64 lines
1.7 KiB
Plaintext
64 lines
1.7 KiB
Plaintext
* Boot executable file loader coded by Fox/Taquart
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* Reads file from ATR prepared with X-BOOT.
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* Professional version - can load file under ROM.
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* Interrupts and ROM are disabled when running loaded program.
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opt h-
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org $480
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bufr equ $400 128-byte buffer
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tp equ $43 Temporary byte
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vc equ $44 Start and end vectors (4 bytes)
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* Boot code
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boot dta b(0,1),a(boot,$e477) Boot header
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mva #0 $22f Make screen blank...
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mva #$52 $2c8 ... and pink ;)
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lda 20 Wait for VBLK
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cmp:req 20
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mwa #rts $2e0 Set default run vector
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dta b({lda a:0}) Skip two bytes
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secrts sec Return with error
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rts rts
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mva:pha >rts $2e3 Set init address...
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mva:pha <rts $2e2 ... and put return address on stack
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ldx #-5 Load header
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hput sta vc+4,x+ Store byte of header
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stx tp
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next inc bufx Increment buffer index
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bpl getx Branch if within buffer
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inw $30a Increment sector number
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mva #$ff ^31 Turn ROM on
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lsr ^4e Enable NMI interrupts
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cli Enable IRQ interrupts
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jsr $e453 Read sector
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bmi secrts Exit on error
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sei Disable IRQ interrupts
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inc ^4e Disable NMI interrupts
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dec ^31 Turn ROM off
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asl bufx Change $80 to $00
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getx lda bufr+$7f Get byte from buffer
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bufx equ *-2 Buffer index
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ldx tp Check if header or block data
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bne hput Branch to store header
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sta (vc,x) Store block data
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inw vc Increment vector
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lda vc+2 Check if end of block reached
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cmp vc
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lda vc+3
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sbc vc+1
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bcs next No: read next byte
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mva #3 ^2f Yes: Reset POKEY...
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init jmp ($2e2) ... and call init routine
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dta c'5.0p' Unused boot sector space
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ert *<>boot+$80 Exactly 128 bytes should be used
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* X-BOOT adds this block at the end of loaded file
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* It changes jmp ($2e2) to jmp ($2e0)
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opt h+
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org init+1
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dta l($2e0)
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end |