mirror of
https://github.com/cc65/cc65.git
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55444b8337
After the removal of the redundant AND in commit
704c8df04f also the
subsequent LDA became redundant.
205 lines
7.2 KiB
ArmAsm
205 lines
7.2 KiB
ArmAsm
;
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; unsigned char kbhit (void);
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;
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; The method to detect a pressed key is based on the documentation in
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; "Section 3 Programmed Key Functions" in "The Challenger Character Graphics
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; Reference Manual"
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; We only want to return true for characters that can be returned by cgetc(),
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; but not for keys like <Shift> or <Ctrl>. Therefore a special handling is
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; needed for the first row. This is implemented by a bit mask that is stored
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; in tmp1 and that is set to zero after the first round.
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;
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.constructor initkbhit
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.export _kbhit
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.include "osic1p.inc"
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.include "extzp.inc"
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.include "zeropage.inc"
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; Internal state that needs to be preserved across calls.
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.segment "EXTZP" : zeropage
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LASTSCAN: .res 1 ; Result of previous keyboard scan
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DBNCCNT: .res 1 ; Debounce counter
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KBDTMP: .res 1 ; Temporary values
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CTRLSHIFT: .res 1 ; State of CTRL and SHIFT keys
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; Initialize one-character buffer that is filled by kbhit()
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.segment "ONCE"
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initkbhit:
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lda #$00
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sta CHARBUF ; No character in buffer initially
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sta LASTSCAN ; Initialize keyboard state
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sta DBNCCNT
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sta KBDTMP
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sta CTRLSHIFT
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rts
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; Routine to get character from keyboard and return it in A.
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; Based on the OSI ROM routine at $FD00 but uses different
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; storage locations to avoid corrupting CC65 run-time code.
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_kbhit: lda CHARBUF ; Check for previously saved character
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beq LFD05
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ldx #$00 ; High byte of return is always zero
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rts ; A contains non-zero character code meaning true
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LFD05: lda #$80 ; Bit mask for initial keyboard row
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LFD06: jsr LFCBE ; Write keyboard row
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jsr LFCC6 ; Read keyboard column
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bne LFD13 ; Branch if a key in this column was pressed
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lsr a ; Otherwise shift mask to next row
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bne LFD06 ; If not done yet, check next row
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beq LFD3A ; Branch if last row reached and no key pressed
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LFD13: lsr a ; Have a key press. Shift LSB into carry
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bcc LFD1F ; Branch if no key pressed in column 0
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txa ; Key pressed in row zero. Get the column data
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and #$20 ; Mask only the bit for <ESC> as it is the only key in row zero that returns key press
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beq LFD3A ; Branch if <ESC> was not the key
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lda #$1B ; Set character to <ESC>
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bne LFD50 ; Do more processing
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LFD1F: jsr LFE86 ; Shift to find bit that is set (in Y)
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tya ; Get bit
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sta KBDTMP ; Save it
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asl a ; Multiply by 7 by shifting left three times (X8)...
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asl a
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asl a
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sec ; ...then subtracting one
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sbc KBDTMP
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sta KBDTMP ; Save value*7 for later lookup in table
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txa ; Get the keyboard column
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lsr a ; Shift out bit zero (only key there is <SHIFT LOCK>)
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asl a ; And shift back
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jsr LFE86 ; Shift to find bit that is set (in Y)
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beq LFD47 ; Branch if no keys pressed
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lda #$00
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LFD3A: sta CTRLSHIFT ; Save state of <CTRL> and shift keys
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LFD3D: sta LASTSCAN
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lda #$02 ; Count used for key debouncing
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sta DBNCCNT
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ldx #$00 ; High byte of return is always zero
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lda #$00 ; Return false
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rts
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LFD47: clc
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tya ; Get bit number of pressed key
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adc KBDTMP ; Add previously calculated offset for keyboard row*7
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tay
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lda LFF3B,y ; Read ASCII code for key from table
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LFD50: cmp LASTSCAN ; Debounce - same as last key scan?
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bne LFD3D ; If not, try again
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dec DBNCCNT ; Decrement debounce counter
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beq LFD5F ; Branch if done debouncing
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jsr LFCDF ; Wait for short delay to debounce keyboard
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beq _kbhit ; Go back and scan keyboard.
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LFD5F: ldx #$64 ; Was <CONTROL> key down?
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cmp CTRLSHIFT
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bne LFD68 ; Branch if not
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ldx #$0F
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LFD68: stx DBNCCNT
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sta CTRLSHIFT
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cmp #$21
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bmi LFDD0 ; Done, return key
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cmp #$5F
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beq LFDD0 ; Done, return key
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lda #$01
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jsr LFCBE ; Write keyboard row
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jsr LFCCF ; Read keyboard column
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sta KBDTMP
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tax
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and #$06
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bne LFDA2
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bit LASTSCAN
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bvc LFDBB
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txa
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eor #$01
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and #$01
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beq LFDBB
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lda #$20
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bit KBDTMP
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bvc LFDC3
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lda #$C0
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bne LFDC3
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LFDA2: bit LASTSCAN
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bvc LFDAA
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txa
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beq LFDBB
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LFDAA: ldy LASTSCAN
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cpy #$31
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bcc LFDB9
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cpy #$3C
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bcs LFDB9
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lda #$F0
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bne LFDBB
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LFDB9: lda #$10
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LFDBB: bit KBDTMP
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bvc LFDC3
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clc
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adc #$C0
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LFDC3: clc
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adc LASTSCAN
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and #$7F
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bit KBDTMP
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bpl LFDD0
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ora #$80
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LFDD0: sta KBDTMP ; Save pressed key and return in A
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sta CHARBUF
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rts
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; Write keyboard row with value in A.
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; Invert the bits before writing.
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; Returns original value of A.
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LFCBE: eor #$FF
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sta KBD
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eor #$FF
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rts
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; Read keyboard column and return in X.
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; Sets Z flag if no keys were pressed.
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; Saves current value of A.
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LFCC6: pha ; Save A
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jsr LFCCF ; Read keyboard column
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tax ; Save in X
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pla ; Restore A
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dex ; Decrement and then increment to
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inx ; preserve value of X but set flags
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rts
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; Read keyboard column.
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; Invert the bits (pressed key(s) will show up as ones).
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LFCCF: lda KBD ; Read keyboard hardware
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eor #$FF ; Invert the bits
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rts
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; Short fixed delay routine.
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LFCDF: ldy #$10
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LFCE1: ldx #$40
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LFCE3: dex
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bne LFCE3
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dey
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bne LFCE1
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rts
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; Shift A left until we find a 1 in the most significant bit.
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; Return the bit number in Y.
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LFE86: ldy #$08
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LFE88: dey
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asl a
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bcc LFE88
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rts
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; Lookup table of keyboard keys for each scan row.
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LFF3B: .byte $BD
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.byte 'P', ';', '/', ' ', 'Z', 'A', 'Q'
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.byte ',', 'M', 'N', 'B', 'V', 'C', 'X'
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.byte 'K', 'J', 'H', 'G', 'F', 'D', 'S'
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.byte 'I', 'U', 'Y', 'T', 'R', 'E', 'W'
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.byte $00, $00, $0D, $0A, 'O', 'L', '.'
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.byte $00, '_', '-', ':', '0', '9', '8'
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.byte '7', '6', '5', '4', '3', '2', '1'
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