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kbd: squeeze out a few bytes

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This commit is contained in:
Virgil Dupras 2019-12-06 22:45:39 -05:00
parent b9292eb8d0
commit 5e0a548faa
1 changed files with 19 additions and 28 deletions
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47
kernel/kbd.asm
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@ -17,9 +17,10 @@
; *** Variables ***
; Set to previously received scan code
.equ KBD_PREV_KC KBD_RAMSTART
; Whether Shift key is pressed
.equ KBD_SHIFT_ON KBD_PREV_KC+1
.equ KBD_RAMEND KBD_SHIFT_ON+1
; Whether Shift key is pressed. When not pressed, holds 0. When pressed, holds
; 0x80. This allows for quick shifting in the glyph table.
.equ KBD_SHIFT_ON @+1
.equ KBD_RAMEND @+1
kbdInit:
xor a
@ -45,58 +46,49 @@ kbdGetC:
cp KBD_KC_BREAK
jr z, .break
cp KBD_KC_EXT
jr z, .ignore
jr z, .nothing
ex af, af' ; restore saved KC
; A scan code over 0x80 is out of bounds or prev KC tell us we should
; skip. Ignore.
cp 0x80
jr nc, .ignore
jr nc, .nothing
; No need to skip, code within bounds, we have something!
call .isShift
jr z, .shiftPressed
; Let's see if there's a ASCII code associated to it.
push hl ; --> lvl 1
ld hl, KBD_SHIFT_ON
bit 0, (hl)
or (hl) ; if shift is on, A now ranges in 0x80-0xff.
ld hl, kbdScanCodes ; no flag changed
jr z, .shiftNotPressed
; Shift is being pressed. Use Shifted table.
ld hl, kbdScanCodesS
.shiftNotPressed:
call addHL
ld a, (hl)
pop hl ; <-- lvl 1
or a
jr z, kbdGetC ; no code. Keep A at 0, but unset Z
jr z, kbdGetC ; no code.
; We have something!
cp a ; ensure Z
ret
.shiftPressed:
ld a, 1
ld a, 0x80
ld (KBD_SHIFT_ON), a
jr .ignore ; to actual char to return
jr .nothing ; no actual char to return
.break:
ex af, af' ; restore saved KC
call .isShift
jr nz, .ignore
jr nz, .nothing
; We had a shift break, update status
xor a
ld (KBD_SHIFT_ON), a
; continue to .ignore
.ignore:
; A scan code over 0x80 is out of bounds or prev KC tell us we should
; skip. Ignore.
xor a
jr kbdGetC
; continue to .nothing
.nothing:
; We have nothing. Before we go further, we'll wait a bit to give our
; device the time to "breathe". When we're in a "nothing" loop, the z80
; hammers the device really fast and continuously generates interrupts
; on it and it interferes with its other task of reading the keyboard.
push bc
ld b, 0
xor a
.wait:
nop
djnz .wait
pop bc
inc a
jr nz, .wait
jr kbdGetC
; Whether KC in A is L or R shift
.isShift:
@ -106,7 +98,7 @@ kbdGetC:
ret
; A list of the values associated with the 0x80 possible scan codes of the set
; 2 of the PS/2 keyboard specs. 0 means no value. That value is a character than
; 2 of the PS/2 keyboard specs. 0 means no value. That value is a character that
; can be read in a GetC routine. No make code in the PS/2 set 2 reaches 0x80.
kbdScanCodes:
; 0x00 1 2 3 4 5 6 7 8 9 a b c d e f
@ -126,8 +118,7 @@ kbdScanCodes:
; 0x70 27 = ESC
.db '0','.','2','5','6','8', 27, 0, 0, 0,'3', 0, 0,'9', 0, 0
; Same values, but shifted
kbdScanCodesS:
; Same values, but shifted, exactly 0x80 bytes after kbdScanCodes
; 0x00 1 2 3 4 5 6 7 8 9 a b c d e f
.db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9,'~', 0
; 0x10 9 = TAB