ti/kbd: begin GetC implementation

For now, only digits are scanned. Lifted from my "tiseg7" example.

ref #41

fonts/5x7.txt

@@ -148,7 +148,7 @@
  ... 
 .    
 .    
- ... 
+.... 
 .   .
 .   .
  ... 

kernel/ti/kbd.asm

@@ -6,22 +6,103 @@
 .equ	KBD_PORT	0x01
 
 ; *** Code ***
+
+; Wait for a digit to be pressed and sets the A register to the value (0-9) of
+; that digit.
+;
+; This routine waits for a key to be pressed, but before that, it waits for
+; all keys to be de-pressed. It does that to ensure that two calls to
+; waitForKey only go through after two actual key presses (otherwise, the user
+; doesn't have enough time to de-press the button before the next waitForKey
+; routine registers the same key press as a second one).
+; 
 ; Sending 0xff to the port resets the keyboard, and then we have to send groups
 ; we want to "listen" to, with a 0 in the group bit. Thus, to know if *any* key
 ; is pressed, we send 0xff to reset the keypad, then 0x00 to select all groups,
 ; if the result isn't 0xff, at least one key is pressed.
-waitForKey:
-	push	af
-
-	ld	a, 0xff
-	out	(KBD_PORT), a
-	ld	a, 0x00
-	out	(KBD_PORT), a
+kbdGetC:
+	push	bc
 
+; loop until a digit is pressed
 .loop:
-	in	a, (KBD_PORT)
-	inc	a		; if a was 0xff, will become 0 (z test)
-	jr	z, .loop	; zero? nothing pressed
+	; When we check for digits, we go through all 3 groups containing them.
+	; for each group, we load the digit we check for in B and then test the
+	; bit for that key. If the bit is reset, our key is pressed. we can
+	; jump to the end, copy B into A and return.
 
-	pop	af
+	; check group 2
+	ld	a, 0xfb
+	call	.get
+
+	ld	b, '3'
+	bit	1, a
+	jr	z, .end
+
+	ld	b, '6'
+	bit	2, a
+	jr	z, .end
+
+	ld	b, '9'
+	bit	3, a
+	jr	z, .end
+
+	ld	a, 0xf7
+	call	.get
+
+	ld	b, '2'
+	bit	1, a
+	jr	z, .end
+
+	ld	b, '5'
+	bit	2, a
+	jr	z, .end
+
+	ld	b, '8'
+	bit	3, a
+	jr	z, .end
+
+	; check group 4
+	ld	a, 0xef
+	call	.get
+
+	ld	b, '0'
+	bit	0, a
+	jr	z, .end
+
+	ld	b, '1'
+	bit	1, a
+	jr	z, .end
+
+	ld	b, '4'
+	bit	2, a
+	jr	z, .end
+
+	ld	b, '7'
+	bit	3, a
+	jr	z, .end
+
+	jr	.loop		; nothing happened? loop
+
+.end:
+	; loop until all keys are de-pressed
+.loop2:
+	xor	a
+	call	.get
+	inc	a		; if a was 0xff, will become 0 (nz test)
+	jr	nz, .loop2	; non-zero? something is pressed
+
+	; copy result into A
+	ld	a, b
+
+	pop	bc
+	ret
+.get:
+	ex	af, af'
+	ld	a, 0xff
+	di
+	out	(KBD_PORT), a
+	ex	af, af'
+	out	(KBD_PORT), a
+	in	a, (KBD_PORT)
+	ei
 	ret

recipes/ti84/glue.asm

@@ -30,7 +30,7 @@
 .inc "ti/lcd.asm"
 .inc "ti/kbd.asm"
 .equ	STDIO_RAMSTART	LCD_RAMEND
-.equ	STDIO_GETC	GetC
+.equ	STDIO_GETC	kbdGetC
 .equ	STDIO_PUTC	lcdPutC
 .inc "stdio.asm"
 
@@ -66,10 +66,6 @@ main:
 	call	shellInit
 	jp	shellLoop
 
-GetC:
-	call	waitForKey
-	jr	boot
-
 handleInterrupt:
 	di
 	push	af