work towards INS key support in MEGA65 mode

src/kernal/screen_m65/mega65_chrout_screen_control.s

@@ -79,8 +79,6 @@ m65_chrout_screen_CLR:
 	nop
 m65_chrout_screen_HOME:
 	nop
-m65_chrout_screen_INS:
-	nop
 m65_chrout_screen_TAB:
 	nop
 m65_chrout_screen_LINE_FEED:

src/kernal/screen_m65/mega65_chrout_screen_control_2.s

@@ -49,3 +49,77 @@ m65_chrout_screen_STOP:
 	sta QTSW
 	sta INSRT
 	jmp_8 m65_chrout_screen_ctrl2_end
+
+
+// INS key
+
+m65_chrout_screen_INS:
+
+	// First prepare the pointer to the current row
+
+	jsr m65_helper_scrlpnt_color
+	jsr m65_helper_scrlpnt_to_screen
+
+	// Check for windowed mode
+
+	lda M65_SCRWINMODE
+	bmi_16 m65_chrout_screen_INS_winmode
+
+	// Check if last character of the line is space
+
+	ldy M65_SCRMODE
+	lda m65_scrtab_txtwidth,y
+	dec_a
+	taz
+	lda_lp (M65_LPNT_SCR), z
+	cmp #$20
+	bne_16 m65_chrout_screen_ctrl2_end
+	phz
+
+	// Last character is space - move the characters
+
+	jsr m65_chrout_screen_INS_copy
+
+	// Store space in the current character cell
+
+	lda #$20
+	sta_lp (M65_LPNT_SCR), z
+
+	// Move the color memory
+
+	jsr m65_helper_scrlpnt_color
+	plz
+	jsr m65_chrout_screen_INS_copy
+
+	// Store current colour in the current character cell
+
+	lda COLOR
+	and #$0F
+	sta_lp (M65_LPNT_SCR), z
+
+	// Increase insert mode count (which causes quote-mode like behaviour) and quit
+
+	inc INSRT
+	jmp_8 m65_chrout_screen_ctrl2_end
+
+m65_chrout_screen_INS_winmode:
+
+	// Check if last character of the line within window is space
+
+	// XXX provide implementation
+
+	jmp_8 m65_chrout_screen_ctrl2_end
+
+
+
+m65_chrout_screen_INS_copy:
+
+	dez
+	lda_lp (M65_LPNT_SCR), z
+	inz
+	sta_lp (M65_LPNT_SCR), z
+	dez
+	cpz M65__TXTCOL
+	bne m65_chrout_screen_INS_copy
+
+	rts