reworked PNT/USER recalculation

STATUS.md

@@ -237,7 +237,7 @@ Not all of them - only these we want to have implemented.
 | `$E544`   | clear screen                 | DONE     |                                                    |
 | `$E50C`   | set cursor position          | PARTIAL  |                                                    |
 | `$E566`   | home cursor                  | DONE     |                                                    |
-| `$E56C`   | set PNTR value               |          |                                                    |
+| `$E56C`   | set PNT and USER values      | DONE     |                                                    |
 | `$E5A0`   | setup VIC II & I/O           | DONE     |                                                    |
 | `$E6B6`   | advance cursor               | NOT DONE |                                                    |
 | `$E701`   | previous line                | NOT DONE |                                                    |

c64/aliases/,aliases_ram_lowmem.s

@@ -153,10 +153,10 @@
 	.label BLNON     = $CF  //          cursor visibility flag
 	.label CRSW      = $D0  //          whether to input from screen or keyboard
 	.label PNT       = $D1  // $D1-$D2  pointer to the current screen line
-	.label PNTR      = $D3  //          current screen X position
+	.label PNTR      = $D3  //          current screen X position (logical column), 0-79
 	.label QTSW      = $D4  //          quote mode flag
 	.label LNMX      = $D5  //          logical line length, [!] our usage probably differs in details
-	.label TBLX      = $D6  //          current screen Y position
+	.label TBLX      = $D6  //          current screen Y position (row), 0-24
 	.label SCHAR     = $D7  //          ASCII value of the last printed character
 	.label INSRT     = $D8  //          insert mode flag/counter
 	.label LDTBL     = $D9  // $D9-$F2  screen line link table, [!] our usage is different  XXX give more details

c64/kernal/screen/clear_screen_real.s

@@ -8,9 +8,6 @@
 
 clear_screen_real:
 
-	// YYY - do we need this? First disable the cursor
-	// jsr cursor_disable
-
 	// Clear the line link table - cheecked on original ROMs,
 	// the highest bit set means that the line is NOT a logical
 	// continuation of the previous one

c64/kernal/screen/e566.cursor_home.s

@@ -9,7 +9,7 @@
 cursor_home:
 
 	lda #$00
-	sta PNTR                           // current column
+	sta PNTR                           // current column (logical)
 	sta TBLX                           // current row
 
 	// FALLTROUGH to the next routine

c64/kernal/screen/e56c.screen_calculate_pnt.s

@@ -1,92 +0,0 @@
-
-//
-// Set pointer (PNT) to current screen line , described in:
-//
-// - [CM64] Computes Mapping the Commodore 64 - page 216
-//
-
-
-screen_calculate_PNT:
-
-	// YYY implement this!
-	rts
-
-
-// Variables: (http://sta.c64.org/cbm64mem.html)
-// - $C7     - RVS    - reverse mode switch
-// - $C8     - INDX   - length of line minus 1 during screen input. Values: $27, 39; $4F, 79.
-// - $C9     - LXSP+0 - cursor row during screen input. Values: $00-$18, 0-24.
-// - $CA     - LXSP+1 - cursor column during screen input. Values: $00-$27, 0-39.
-// - $CC     - BLNSW  - cursor visibility switch. Values: $01-$FF: Cursor is off.
-// - $CD     - BLNCT  - delay counter for changing cursor phase. Values:
-// - $CE     - GDBLN  - screen code of character under cursor
-// - $CF     - BLNON  - cursor phase switch
-// - $D0     - CRSW   - end of line switch during screen input
-// - $D1-$D2 - PNT    - pointer to current line in screen memory.
-// - $D3     - PNTR   - current cursor column. Values: $00-$27, 0-39.
-// - $D4     - QTSW   - quotation mode switch
-// - $D5     - LNMX   - length of current screen line minus 1. Values: $27, 39; $4F, 79.
-// - $D6     - TBLX   - current cursor row. Values: $00-$18, 0-24.
-// - $D8     - INSRT  - number of insertions
-// - $D9-$F1 - LDTBL  - link table
-// - $F2              - temporary value for screen scroll
-// - $F3-$F4 - USER   - pointer to current line in Color RAM.
-// - $02A5   - TLNIDX - number of line currently being scrolled during scrolling the screen
-
-
-/* YYY disabled for rework
-
-screen_calculate_line_pointer:
-	jsr screen_normalize_xy
-	
-	//  Reset pointer to start of screen
-	lda HIBASE
-	sta PNT+1
-	lda #0
-	sta PNT+0
-
-	// Add 40 for every line, or 80 if the lines are linked
-	ldx TBLX
-
-!:
-	// Stop if we have counted enough lines
-	beq !+
-
-	// Add 40 or 80 based on whether the line is linked
-	// or not.
-	ldy #40
-	// -1 offset is because we count down from N to 1, not
-	// N-1 to 0.
-	lda LDTBL-1,x
-	bpl sclp_l1
-	ldy #80
-sclp_l1:
-	// Add computed line length to pointer value
-	tya
-	clc
-	adc PNT+0
-	sta PNT+0
-	lda PNT+1
-	adc #0
-	sta PNT+1
-	
-	// Loop back to next line
-	dex
-	jmp !-
-!:
-
-	// FALLTHROUGH
-
-update_colour_line_pointer:
-	// Now setup pointer to colour RAM
-	lda PNT+0
-	sta USER+0
-	lda PNT+1
-	sec
-	sbc HIBASE
-	clc
-	adc #>$d800
-	sta USER+1
-
-	rts
-*/

c64/kernal/screen/e56c.screen_calculate_pnt_user.s

@@ -0,0 +1,51 @@
+
+//
+// Set pointer (PNT) to current screen line , described in:
+//
+// - [CM64] Computes Mapping the Commodore 64 - page 216
+// - http://sta.c64.org/cbm64scrfunc.html
+//
+
+
+screen_calculate_PNT_USER:
+
+	// YYY jsr screen_normalize_xy - do we need this? probably not
+
+	// Reset pointer to start of screen
+
+	lda HIBASE
+	sta PNT+1
+	lda #$00
+	sta PNT+0
+
+	// Add 40 to PNT for every line
+
+	ldx TBLX
+	beq screen_calculate_USER
+!:
+	lda #40
+	clc
+	adc PNT+0
+	sta PNT+0
+	bcc !+
+	inc PNT+1
+!:
+	dex
+	bne !--
+
+	// FALLTROUGH
+
+screen_calculate_USER:
+
+	// Calculate USER (pointer to the current line in color RAM)
+
+	lda PNT+0
+	sta USER+0
+	lda PNT+1
+	sec
+	sbc HIBASE
+	clc
+	adc #>$d800
+	sta USER+1
+
+	rts