kbd: simplify code

kernel/kbd.asm

@@ -8,15 +8,23 @@
 ; 0 when nothing was typed.
 ; KBD_FETCHKC
 
+; *** Consts ***
+.equ	KBD_KC_BREAK	0xf0
+.equ	KBD_KC_EXT	0xe0
+.equ	KBD_KC_LSHIFT	0x12
+.equ	KBD_KC_RSHIFT	0x59
+
 ; *** Variables ***
-.equ	KBD_SKIP_NEXT	KBD_RAMSTART
-; Pointer to a routine that fetches the last typed keyword in A. Should return
-; 0 when nothing was typed.
-.equ	KBD_RAMEND	KBD_SKIP_NEXT+1
+; 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
 
 kbdInit:
 	xor	a
-	ld	(KBD_SKIP_NEXT), a
+	ld	(KBD_PREV_KC), a
+	ld	(KBD_SHIFT_ON), a
 	ret
 
 kbdGetC:
@@ -26,20 +34,24 @@ kbdGetC:
 
 	; scan code not zero, maybe we have something.
 	; Do we need to skip it?
-	push	af		;  <|
-	ld	a, (KBD_SKIP_NEXT) ;|
-	or	a		;   |
-	jr	nz, .skip	;   |
-	pop	af		;  <|
+	ex	af, af'		; save fetched KC
+	ld	a, (KBD_PREV_KC)
+	; If F0 (break code) or E0 (extended code), we skip this code
+	cp	KBD_KC_BREAK
+	jr	z, .skip
+	cp	KBD_KC_EXT
+	jr	z, .skip
+	ex	af, af'		; restore saved KC
+	ld	(KBD_PREV_KC), a
 	cp	0x80
 	jr	nc, .outOfBounds
 	; No need to skip, code within bounds, we have something! Let's see if
 	; there's a ASCII code associated to it.
-	push	hl		; <|
-	ld	hl, kbdScanCodes ; |
-	call	addHL		;  |
-	ld	a, (hl)		;  |
-	pop	hl		; <|
+	push	hl		; --> lvl 1
+	ld	hl, kbdScanCodes
+	call	addHL
+	ld	a, (hl)
+	pop	hl		; <-- lvl 1
 	or	a
 	jp	z, unsetZ	; no code. Keep A at 0, but unset Z
 	; We have something!
@@ -47,21 +59,11 @@ kbdGetC:
 	ret
 .outOfBounds:
 	; A scan code over 0x80 is out of bounds. Ignore.
-	; If F0 (break code) or E0 (extended code), we also skip the next code
-	cp	0xf0
-	jr	z, .skipNext
-	cp	0xe0
-	jr	z, .skipNext
-	xor	a
-	jp	unsetZ
-.skipNext:
-	ld	(KBD_SKIP_NEXT), a
 	xor	a
 	jp	unsetZ
 .skip:
-	pop	af		; equilibrate stack
 	xor	a
-	ld	(KBD_SKIP_NEXT), a
+	ld	(KBD_PREV_KC), a
 	jp	unsetZ
 .nothing:
 	; We have nothing. Before we go further, we'll wait a bit to give our