begin implementing basic text manipulation routines.

c64/basic/,aliases.s

@@ -25,6 +25,7 @@
 	.alias basic_start_of_free_space_ptr $31
 	.alias basic_start_of_strings_ptr $33
 	.alias basic_top_of_memory_ptr $37
+	.alias basic_current_line_ptr $3d
 	
 	.alias basic_numeric_work_area $57 ; $57 - $60 inclusive = 10 bytes
 
@@ -115,3 +116,15 @@
 	.alias enable_case_switch $0291
 	.alias screen_scroll_disable $0292
 	.alias pal_or_ntsc $02A6
+
+
+	;; BASIC uses some extra bytes for memory access under ROMs located at $2A7 onwards
+	;; IRQs are disabled when doing such accesses, and a default NMI handler only increments
+	;; a counter, so that if an NMI occurs, it doesn't crash the machine, but can be captured.
+	.alias missed_nmi_flag         $2A7
+	.alias tiny_nmi_handler		$2A8	
+	.alias peek_under_roms tiny_nmi_handler+peek_under_roms_routine-tiny_nmi_handler_routine
+	.alias poke_under_roms tiny_nmi_handler+poke_under_roms_routine-tiny_nmi_handler_routine
+	.alias memmap_allram tiny_nmi_handler+memmap_allram_routine-tiny_nmi_handler_routine
+	.alias memmap_normal tiny_nmi_handler+memmap_normal_routine-tiny_nmi_handler_routine
+	

c64/basic/basic_delete_line.s

@@ -0,0 +1,9 @@
+	;; Delete the current BASIC line, which is assumed to have already
+	;; been found with basic_find_line.
+	;; Really only consists of copying memory down.
+	;; The only complication is that we have to do the copy with ROMs
+	;; banked out. Oh, yes, and we have to update all the links in
+	;; the following basic lines.
+basic_delete_line:
+	sec
+	rts

c64/basic/basic_find_line.s

@@ -0,0 +1,46 @@
+	;; Find the BASIC line with number basic_line_number
+
+
+basic_find_line:
+	;; Get pointer to start of BASIC text
+	lda basic_start_of_text_ptr+0
+	sta basic_current_line_ptr+0
+	lda basic_start_of_text_ptr+1
+	sta basic_current_line_ptr+1
+
+basic_find_line_loop:	
+	;; Then search for line number
+	;; Line number 
+	ldy #2
+	ldx #<basic_current_line_ptr
+	jsr peek_under_roms
+	cmp basic_line_number+0
+	bne not_this_line
+	iny
+	jsr peek_under_roms
+	cmp basic_line_number+1
+	bne not_this_line
+
+	clc
+	rts
+not_this_line:
+	;; Not this line, so advance to next line
+	ldy #0
+	ldx #<basic_current_line_ptr
+	jsr peek_under_roms
+	bne more_lines_exist
+	iny
+	jsr peek_under_roms
+	bne more_lines_exist
+	;; no more lines exist, return failure
+	sec
+	rts
+more_lines_exist:	
+	;; A = high byte of line
+	pha
+	dey
+	jsr peek_under_roms
+	sta basic_current_line_ptr+0
+	pla
+	sta basic_current_line_ptr+1
+	jmp basic_find_line_loop

c64/basic/basic_insert_line.s

@@ -0,0 +1,11 @@
+	;; Insert the tokenised line stored at $0200.
+	;; First work out where in the list to put it
+	;; (basic_find_line with the line number can be used to work
+	;; out the insertion point, as it should abort once it finds a
+	;; line number too high).
+	;; Then all we have to do is push the rest of the BASIC text up,
+	;; and update the pointers in all following basic lines.
+basic_insert_line:
+	sec
+	rts
+	

c64/basic/basic_main_loop.s

@@ -91,6 +91,12 @@ ml_bad_line_number:
 
 	;; Got a valid line number.
 
+	;; First, clear all variables, so that we only have to shove BASIC text around.
+	;; (We could later remove this requirement, and the only effect should be
+	;; to slow things down, and that you might have to either CLR if there is no
+	;; memory free, or else it would auto CLR when you ran out of program space).
+	jsr basic_do_clr
+
 	;; Copy to line number holder
 	lda basic_fac1_mantissa+0
 	sta basic_line_number+0
@@ -98,8 +104,12 @@ ml_bad_line_number:
 	sta basic_line_number+1
 
 	;; Delete line if present
-
+	jsr basic_find_line
+	bcs +
+	jsr basic_delete_line
+*
 	;; Insert new line if non-zero length
+	jsr basic_insert_line
 	
 not_a_line:	
 	

c64/basic/basic_warm_start.s

@@ -1,5 +1,7 @@
 	;; Clear screen etc, show READY prompt.
 
 basic_warm_start:
+	jsr install_ram_routines
+	
 	jmp basic_main_loop
 	

c64/basic/under_rom_routines.s

@@ -0,0 +1,57 @@
+	;; IMPORTANT:
+	;; These routines lengths cannot be changed without changing
+	;; the aliases for peek_under_roms, poke_under_roms etc
+	;; in ,aliases.s.
+	;; Thus those addresses are expressed using formulae.
+
+install_ram_routines:
+	;; Copy routines into place
+	ldx #ram_routines_len-1
+*
+	lda ram_routines_start,x
+	sta tiny_nmi_handler,x
+	dex
+	bpl -
+
+	;; Point NMI handler to tiny_nmi_handler
+	lda #<tiny_nmi_handler
+	sta $FFFE
+	lda #>tiny_nmi_handler
+	sta $FFFF
+
+	rts
+	
+ram_routines_start:	
+
+tiny_nmi_handler_routine:
+	inc missed_nmi_flag
+	rti
+
+peek_under_roms_routine:
+	stx peek_under_roms+7 	;Offset of arg of lda ($00),y
+	jsr memmap_allram
+	lda ($00),y
+	jmp memmap_normal
+
+poke_under_roms_routine:
+	stx poke_under_roms+7 	;Offset of arg of lda ($00),y
+	jsr memmap_allram
+	sta ($00),y
+	;; FALL THROUGH
+memmap_normal_routine:
+	pha
+	lda #$37
+	sta $01
+	pla
+	cli
+	rts
+
+memmap_allram_routine:
+	sei
+	lda #$04
+	sta $01
+	rts
+
+ram_routines_end:
+	.alias ram_routines_len ram_routines_end-ram_routines_start
+