further work on new keyboard scanning routine

c64/kernal/keyboard/scnkey.s

@@ -20,20 +20,19 @@
 // - MODE    - flag, whether charset toggle (SHIFT+VENDOR) is allowed
 
 
+// XXX add Commodore 128 keyboard support
+// XXX add Commodore 65 keybopard support
+// XXX add support for using joystick to move sursor keys
+// XXX prevent joystick port 1 interference
+
 #if !CONFIG_SCNKEY_TWW_CTR
 
-// Routine is heavily inspired by TWW/CTR proposal, see here:
+// Routine takes some ideas from TWW/CTR proposal, see here:
 // - http://codebase64.org/doku.php?id=base:scanning_the_keyboard_the_correct_and_non_kernal_way
 
 
 SCNKEY:
 
-	// Handle repeat timer
-
-	lda KOUNT
-	beq !+
-	dec KOUNT
-!:
 	// Prepare for SHFLAG update
 
 	lda SHFLAG
@@ -47,11 +46,12 @@ SCNKEY:
 
 	lda #$00
 	sta CIA1_PRA  // connect all the rows
-	lda #$FF
-	cmp CIA1_PRB
+	ldx #$FF
+	cpx CIA1_PRB
 	beq scnkey_no_keys
 
 	// Retrieve SHIFT / VENDOR / CTRL status
+	// Use .X to detect 2 or more keys pressed (should be $FF now)
 	ldy #$03
 scnkey_bucky_loop:
 	lda kb_matrix_bucky_confmask, y
@@ -70,34 +70,69 @@ scnkey_bucky_loop:
 
 	jsr scnkey_via_keylog // XXX for some CPUs we have indirect jsr
 
+	// XXX check if there is space in keyboard buffer
 	// XXX check for joystick activity
 
 	// Scan the keyboard matrix
 
-	ldy #$07
+	ldy #$07 // XXX adapt for C128 and C65 keyboards
+	ldx #$FF                       // offset in key matrix table, $FF for not found yet
 scnkey_matrix_loop:
 	lda kb_matrix_row_keys, y
 	sta CIA1_PRA
-	lda kb_matrix_bucky_filter, y
+	lda kb_matrix_bucky_filter, y  // filter out bucky keys
 	ora CIA1_PRB
-
-	// XXX
+	cmp #$FF
+	beq scnkey_matrix_loop_next    // skip if no key pressed from this row
+	cpx #$FF
+	bne scnkey_no_keys             // clash, more than one key pressed
+	// We have at least one key pressed in this row, we need to find which one exactly
+	ldx #$07
+scnkey_matrix_loop_inner:
+	cmp kb_matrix_row_keys, x
+	bne !+                         // not this particular key
+	txa                            // now .A contains key offset within a row
+	sec
+	adc kb_matrix_row_offsets, y   // now .A contains key offset from the matrix start
+	tax
+	jmp scnkey_matrix_loop_next
+!:
+	dex
+	bpl scnkey_matrix_loop_inner
+	bmi scnkey_no_keys            // branch always, multiple keys must have been pressed
+scnkey_matrix_loop_next:
 	dey
 	bpl scnkey_matrix_loop
 
+	// Scanning complete
 
+	cpx #$FF
+	bne scnkey_got_key
 
-
-
-	// XXX
+	// FALLTROUGH
 
 scnkey_no_keys:
 
-	lda #$FF
+	// XXX
+
+	lda #$40 // XXX adapt value for C128 and C65 keyboards
 	sta LSTX
 
 	rts
 
+scnkey_got_key: // .X should now contain the key offset in matrix pointed by KEYTAB
+
+	// Handle repeat timer
+
+	.break
+	lda KOUNT
+	beq !+
+	dec KOUNT
+!:
+
+	// XXX
+	rts
+
 scnkey_via_keylog:
 	jmp (KEYLOG)