more work on MEGA65 keyboard scanner

src/kernal/keyboard_m65/mega65_scnkey.s

@@ -4,4 +4,109 @@
 
 m65_scnkey:
 
+	; First scan the whole keyboard
+
+	lda KBSCN_BUCKY
+	sta M65_KB_BUCKY
+
+	ldx #$08
+@1:
+	stx KBSCN_SELECT
+	lda KBSCN_PEEK
+	eor #$FF                           ; let bit 1 mean 'pressed', not the otherwise
+	sta M65_KB_COLSCAN, x
+	dex
+	bpl @1
+
+	; Update the SHFLAG
+
+	lda SHFLAG
+	sta LSTSHF                         ; needed for SHIFT+VENDOR support
+
+	ldy #$00                           ; the new SHFLAG will be constructed in .Y
+	ldx M65_KB_BUCKY
+	beq m65_scnkey_SHFLAG_ready
+
+	; FALLTROUGH
+
+m65_scnkey_detect_SHIFT:
+
+	txa
+	and #%00000011
+	beq m65_scnkey_detect_VENDOR
+
+	tya
+	ora #KEY_FLAG_SHIFT
+	tay
+
+	; FALLTROUGH
+
+m65_scnkey_detect_VENDOR:
+	
+	txa
+	and #%00001000
+	beq m65_scnkey_detect_CTRL
+
+	tya
+	ora #KEY_FLAG_VENDOR
+	tay
+
+	; FALLTROUGH
+
+m65_scnkey_detect_CTRL:
+	
+	txa
+	and #%00000100
+	beq m65_scnkey_detect_ALT
+
+	tya
+	ora #KEY_FLAG_CTRL
+	tay
+
+	; FALLTROUGH
+
+m65_scnkey_detect_ALT:
+	
+	txa
+	and #%00010000
+	beq m65_scnkey_detect_CAPS_LOCK
+
+	tya
+	ora #KEY_FLAG_ALT
+	tay
+
+	; FALLTROUGH
+
+m65_scnkey_detect_CAPS_LOCK:
+	
+	txa
+	and #%01000000
+	beq m65_scnkey_detect_NO_SCRL
+
+	tya
+	ora #KEY_FLAG_NO_SCRL
+	tay
+
+	; FALLTROUGH
+
+m65_scnkey_detect_NO_SCRL:
+	
+	txa
+	and #%00100000
+	beq m65_scnkey_SHFLAG_ready
+
+	tya
+	ora #KEY_FLAG_CAPSL
+	tay
+
+	; FALLTROUGH
+
+m65_scnkey_SHFLAG_ready:
+
+	sty SHFLAG
+	
+
+	; XXX
+
+
 	rts