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kbd: squeeze out a few bytes
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@ -17,9 +17,10 @@
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; *** Variables ***
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; Set to previously received scan code
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.equ KBD_PREV_KC KBD_RAMSTART
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; Whether Shift key is pressed
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.equ KBD_SHIFT_ON KBD_PREV_KC+1
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.equ KBD_RAMEND KBD_SHIFT_ON+1
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; Whether Shift key is pressed. When not pressed, holds 0. When pressed, holds
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; 0x80. This allows for quick shifting in the glyph table.
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.equ KBD_SHIFT_ON @+1
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.equ KBD_RAMEND @+1
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kbdInit:
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xor a
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@ -45,58 +46,49 @@ kbdGetC:
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cp KBD_KC_BREAK
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jr z, .break
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cp KBD_KC_EXT
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jr z, .ignore
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jr z, .nothing
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ex af, af' ; restore saved KC
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; A scan code over 0x80 is out of bounds or prev KC tell us we should
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; skip. Ignore.
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cp 0x80
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jr nc, .ignore
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jr nc, .nothing
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; No need to skip, code within bounds, we have something!
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call .isShift
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jr z, .shiftPressed
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; Let's see if there's a ASCII code associated to it.
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push hl ; --> lvl 1
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ld hl, KBD_SHIFT_ON
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bit 0, (hl)
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or (hl) ; if shift is on, A now ranges in 0x80-0xff.
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ld hl, kbdScanCodes ; no flag changed
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jr z, .shiftNotPressed
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; Shift is being pressed. Use Shifted table.
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ld hl, kbdScanCodesS
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.shiftNotPressed:
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call addHL
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ld a, (hl)
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pop hl ; <-- lvl 1
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or a
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jr z, kbdGetC ; no code. Keep A at 0, but unset Z
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jr z, kbdGetC ; no code.
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; We have something!
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cp a ; ensure Z
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ret
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.shiftPressed:
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ld a, 1
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ld a, 0x80
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ld (KBD_SHIFT_ON), a
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jr .ignore ; to actual char to return
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jr .nothing ; no actual char to return
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.break:
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ex af, af' ; restore saved KC
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call .isShift
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jr nz, .ignore
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jr nz, .nothing
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; We had a shift break, update status
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xor a
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ld (KBD_SHIFT_ON), a
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; continue to .ignore
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.ignore:
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; A scan code over 0x80 is out of bounds or prev KC tell us we should
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; skip. Ignore.
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xor a
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jr kbdGetC
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; continue to .nothing
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.nothing:
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; We have nothing. Before we go further, we'll wait a bit to give our
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; device the time to "breathe". When we're in a "nothing" loop, the z80
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; hammers the device really fast and continuously generates interrupts
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; on it and it interferes with its other task of reading the keyboard.
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push bc
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ld b, 0
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xor a
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.wait:
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nop
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djnz .wait
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pop bc
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inc a
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jr nz, .wait
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jr kbdGetC
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; Whether KC in A is L or R shift
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.isShift:
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@ -106,7 +98,7 @@ kbdGetC:
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ret
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; A list of the values associated with the 0x80 possible scan codes of the set
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; 2 of the PS/2 keyboard specs. 0 means no value. That value is a character than
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; 2 of the PS/2 keyboard specs. 0 means no value. That value is a character that
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; can be read in a GetC routine. No make code in the PS/2 set 2 reaches 0x80.
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kbdScanCodes:
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; 0x00 1 2 3 4 5 6 7 8 9 a b c d e f
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@ -126,8 +118,7 @@ kbdScanCodes:
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; 0x70 27 = ESC
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.db '0','.','2','5','6','8', 27, 0, 0, 0,'3', 0, 0,'9', 0, 0
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; Same values, but shifted
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kbdScanCodesS:
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; Same values, but shifted, exactly 0x80 bytes after kbdScanCodes
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; 0x00 1 2 3 4 5 6 7 8 9 a b c d e f
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.db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9,'~', 0
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; 0x10 9 = TAB
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