65 lines
1.4 KiB
ArmAsm
65 lines
1.4 KiB
ArmAsm
|
|
cmd_new:
|
|
jsr basic_do_new
|
|
jmp basic_main_loop
|
|
|
|
cmd_clr:
|
|
jsr basic_do_clr
|
|
jmp basic_main_loop
|
|
|
|
basic_do_new:
|
|
;; Setup pointers to memory storage
|
|
lda #<$0801
|
|
sta basic_start_of_text_ptr+0
|
|
lda #>$0801
|
|
sta basic_start_of_text_ptr+1
|
|
sta basic_start_of_vars_ptr+1
|
|
lda #<$0803
|
|
sta basic_start_of_vars_ptr+0
|
|
|
|
;; Zero line pointer
|
|
;; XXX - We should also zero $0800, i.e., basic_start_of_text_ptr - 1
|
|
ldy #$00
|
|
tya
|
|
sta (basic_start_of_text_ptr),y
|
|
iny
|
|
sta (basic_start_of_text_ptr),y
|
|
|
|
|
|
;; Get top of memory.
|
|
;; If a cart is present, then it is $7FFF,
|
|
;; if not, then it is $F7FF, since we support having
|
|
;; programs and variables under ROM.
|
|
;; i.e., we support 56KB RAM for BASIC, keeping some space
|
|
;; free for some optimisation structures, e.g., FOR/NEXT loop
|
|
;; records (without them going on the stack), GOSUB stack
|
|
;; (same story), expression value cache?
|
|
|
|
sec ; Read, not write value
|
|
jsr $ff99 ; KERNAL MEMTOP routine
|
|
cpx #$80
|
|
bne +
|
|
lda #>$f7ff
|
|
.byte $2c
|
|
* lda #>$7FFF
|
|
sta basic_top_of_memory_ptr+1
|
|
sta basic_start_of_strings_ptr+1
|
|
lda #<$f7ff
|
|
sta basic_top_of_memory_ptr+0
|
|
sta basic_start_of_strings_ptr+0
|
|
|
|
;; FALL THROUGH
|
|
|
|
basic_do_clr:
|
|
;; Clear variables, arrays and strings
|
|
lda basic_start_of_vars_ptr+0
|
|
sta basic_start_of_arrays_ptr+0
|
|
sta basic_start_of_free_space_ptr+0
|
|
lda basic_start_of_vars_ptr+1
|
|
sta basic_start_of_arrays_ptr+1
|
|
sta basic_start_of_free_space_ptr+1
|
|
|
|
rts
|
|
|
|
|