more work towards MEGA65 native mode screen support

src/aliases/,aliases_ram_lowmem_m65.s

@@ -20,6 +20,13 @@
 	.label M65_LPNT_KERN = $EE  // $EE-$F1  4-byte pointer for temporary usage by KERNAL
 	.label M65_TMP__K2   = $F2  // $F2      -- UNUSED -- temporary value for various Kernal routines
 
+	//
+	// Page 0 - other reused values
+	//
+
+	.label M65__TXTROW   = PNTR //          screen row
+	.label M65__TXTCOL   = TBLX //          screen column
+
 	//
 	// Pages 4-7 - reused screen memory
 	//

src/kernal/board_m65/mega65_imports.s

@@ -22,6 +22,7 @@
 .label return_from_interrupt           = KERNAL_0.return_from_interrupt
 .label clrchn_reset                    = KERNAL_0.clrchn_reset
 .label udtim_keyboard                  = KERNAL_0.udtim_keyboard
+.label chrout_to_screen_code           = KERNAL_0.chrout_to_screen_code
 
 .label setup_irq_timer                 = KERNAL_0.setup_irq_timer
 .label wait_x_bars                     = KERNAL_0.wait_x_bars

src/kernal/screen/chrout_screen.s

@@ -26,49 +26,16 @@ chrout_screen:
 	// ones are always printable characters; separate away control codes
 
 	and #$60
-	bne !+
+	beq_16 chrout_screen_control
-	jmp chrout_screen_control
-!:
 	txa
 
 	// Literals - first convert PETSCII to screen code
 
-	// Codes $C0-$DF become $40-$5F
+	jsr chrout_to_screen_code
-	cmp #$E0
-	bcs !+
-	cmp #$C0
-	bcc !+
-	
-	and #$7F
-	jmp chrout_screen_literal // not high char
-
-!:
-	// Range $20-$3F is unchanged
-	cmp #$40
-	bcc chrout_screen_literal // not high char
-
-	// Unshifted letters and symbols from $40-$5F
-	// all end up being -$40
-	// (C64 PRG p376)
-
-	// But anything >= $80 needs to be -$40
-	// (C64 PRG p380-381)
-	// And bit 7 should be cleared, only to be
-	// set by reverse video
-	sec
-	sbc #$40
-
-	// Fix shifted chars by adding $20 again
-	cmp #$20
-	bcc chrout_screen_literal // not high char
-	cmp #$40
-	bcs chrout_screen_literal // not high char
-	clc
-	adc #$20
 
 	// FALLTROUGH
 
-chrout_screen_literal:
+chrout_screen_literal: // entry point for chrout_screen_quote
 
 	// Write normal character on the screen
 

src/kernal/screen/chrout_to_screen_code.s

@@ -0,0 +1,44 @@
+// #LAYOUT# STD *        #TAKE
+// #LAYOUT# *   KERNAL_0 #TAKE
+// #LAYOUT# *   *        #IGNORE
+
+//
+// CHROUT routine - convert PETSCII to screen code
+//
+
+
+chrout_to_screen_code:
+
+	// Codes $C0-$DF become $40-$5F
+	cmp #$E0
+	bcs !+
+	cmp #$C0
+	bcc !+
+	
+	and #$7F
+	rts                                // not high char
+!:
+	// Range $20-$3F is unchanged
+	cmp #$40
+	bcc !+                             // not high char
+
+	// Unshifted letters and symbols from $40-$5F
+	// all end up being -$40
+	// (C64 PRG p376)
+
+	// But anything >= $80 needs to be -$40
+	// (C64 PRG p380-381)
+	// And bit 7 should be cleared, only to be
+	// set by reverse video
+	sec
+	sbc #$40
+
+	// Fix shifted chars by adding $20 again
+	cmp #$20
+	bcc !+                             // not high char
+	cmp #$40
+	bcs !+                             // not high char
+	clc
+	adc #$20
+!:
+	rts

src/kernal/screen_m65/mega65_chrout_screen.s

@@ -1,9 +1,40 @@
 // #LAYOUT# M65 KERNAL_1 #TAKE
 // #LAYOUT# *   *        #IGNORE
 
+//
+// CHROUT routine - screen support (character output), MEGA65 native mode version
+//
+
 
 m65_chrout_screen:
 
-	// XXX provide implementation
+	// XXX hide cursor if visible
+
+	lda SCHAR
+	tax
+
+	// All the PETSCII control codes are within $0x, $1x, $8x, $9x, remaining
+	// ones are always printable characters; separate away control codes
+
+	and #$60
+	beq_16 m65_chrout_screen_control
+	txa
+
+	// Literals - first convert PETSCII to screen code
+
+	jsr chrout_to_screen_code
+
+	// FALLTROUGH
+
+m65_chrout_screen_literal: // entry point for m65_chrout_screen_quote
+
+	// Write normal character on the screen
+
+	tax                                // store screen code, we need .A for calculations
+
+	// XXX continue the implementation
+
+
+
 
 	rts

src/kernal/screen_m65/mega65_chrout_screen_control.s

@@ -0,0 +1,9 @@
+// #LAYOUT# M65 KERNAL_1 #TAKE
+// #LAYOUT# *   *        #IGNORE
+
+
+m65_chrout_screen_control:
+
+	// XXX provide implementation
+
+	rts

src/kernal/screen_m65/mega65_clrscr.s

@@ -113,6 +113,10 @@ m65_clrscr_loop:
 
     // Set screen variables
 
-	// XXX implement this, together with HOME
+	// XXX provide proper implementation, together with HOME
+
+	lda #$00
+	sta M65__TXTROW
+	sta M65__TXTCOL
 
 	rts