add documentation
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1 changed files with 33 additions and 7 deletions
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;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
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;;This program reads a data stream from the joystick port and saves it in memory.
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;;The datastream format is as sutch:
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;;
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;;############################################
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;; 16-bit byte-length (big endian) | data
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;;############################################
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;; The data comes from CTRL2 bit 0 and the clock is at bit 1
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;; The stream starts when the clock is pulled high, after that comes a
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;; 16-bit big endian number that matches the byte-lenght of the data that will get sent.
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;; When the hole stream has ended the clock is pulled low until the next stream!
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;; The data is then stored in ram with the first byte in progdest and the last in progdest + byte-length
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;; At the end the program run the code stored at progdest with a jmp!
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;; More documentation on the Joystick port can be found here: https://www.c64-wiki.com/wiki/Joystick
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CLKMASK = %00000010
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CTRL2 = $DC00
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.org $80d
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coldstart:
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coldstart: ;; Draw a dollar sign on screen to show that program has loaded
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lda #$0
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sta $400
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waitstart:
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waitstart: ;; Wait until joystick 1 has been pulled forwards to start this program
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lda $dc01
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and #$01
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bne waitstart
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;; Change boarder colour for debuging
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lda #$00
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sta $d020
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teststart:
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jsr check_for_load_start
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bcs @error
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jsr check_for_load_start ; Check if start_bit is correct
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bcs @error ; Idk why C=1 ask john
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beq teststart
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jmp $c000
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jmp $c000 ; starts the program?
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jmp $c000
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@error:
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lda #1
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sta $0400
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sta $0400 ;lets store 1 att this address for debuging purposes
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rts
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check_for_load_start:
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lda #CLKMASK
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bit CTRL2
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bne start
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bne start ; branch if Z ==0 <--> CTRL2 and CLKMASK ==0 <---> CTRL2 bit 2 == 0
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lda #$00
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rts
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start:
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sei
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;; change boarder collor for debuging purposes
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ldx #$02
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stx $d020
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ldy #$00
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@ -85,6 +109,8 @@ wait_for_bit_start:
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jmp done
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@notdone:
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new_byte:
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;; BYTE is the byte beaing read from the stream. The bits are shifted from the left
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;; When we shift out this 1 in BYTE bellow we save the BYTE to memory.
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lda #%10000000
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sta BYTE
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wait_for_bit_end:
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