88 lines
2.7 KiB
NASM
88 lines
2.7 KiB
NASM
; 64 byte char buffer
|
|
; Changes are copyright Ben Chong and freely licensed to the community
|
|
;---------------------------------------------------------------------
|
|
; Compare Result N Z C
|
|
; A, X, or Y < Memory * 0 0
|
|
; A, X, or Y = Memory 0 1 1
|
|
; A, X, or Y > Memory * 0 1
|
|
;---------------------------------------------------------------------
|
|
|
|
MAXCOUNT = 64
|
|
HIWATER = 40
|
|
LOWATER = 20
|
|
|
|
inptr = $e7 ;$380 ;$f2
|
|
outptr = $e8 ;$381 ;$f3
|
|
charcount = $e9 ;$382 ;$f4
|
|
|
|
;---------------------------------------------------------------------
|
|
; Initialize buffer operations
|
|
|
|
init_buffer
|
|
lda #$00
|
|
sta inptr
|
|
sta outptr
|
|
sta charcount
|
|
rts
|
|
|
|
;---------------------------------------------------------------------
|
|
; Store char in buffer
|
|
; Entry: A = char
|
|
put_buffer
|
|
pha
|
|
lda charcount
|
|
cmp #MAXCOUNT ; Are we at max?
|
|
bcs bp_max ; Yes, abort
|
|
cmp #HIWATER ;
|
|
bcc not_hiw ; Not high water mark
|
|
jsr uart_deassert_rts
|
|
not_hiw
|
|
inc charcount
|
|
; stx ysav ; Temp storage. 6502 doesn't have enough flexibility...!
|
|
ldx inptr ; Grab inptr from memory
|
|
pla ; Get char
|
|
sta buffer, x ; Store in buffer
|
|
inx ; Increment to next location
|
|
cpx #MAXCOUNT ; Top of buffer area?
|
|
bcc pb_not ; < 64
|
|
ldx #$00 ; If >=64, go back to bottom of buffer
|
|
pb_not
|
|
stx inptr ; Update inptr in memory
|
|
; ldx ysav ; Restore X
|
|
bp_max
|
|
rts
|
|
|
|
;---------------------------------------------------------------------
|
|
; Check if char in buffer, C=1 char, C=0 no character
|
|
; Exit: A contains char
|
|
pull_buffer
|
|
sei ; Disable IRQ
|
|
lda charcount
|
|
beq plb_nochar ; No character in buffer
|
|
dec charcount
|
|
cmp #LOWATER
|
|
bcs not_low ; Not low water
|
|
jsr uart_assert_rts
|
|
not_low
|
|
stx ysav ; Save x
|
|
ldx outptr
|
|
lda buffer, x
|
|
inx
|
|
cpx #MAXCOUNT ; Top of buffer?
|
|
bcc plb_not ; No
|
|
ldx #$00 ; Back to bottom
|
|
plb_not
|
|
stx outptr ; Save
|
|
ldx ysav ; Restore x
|
|
sec
|
|
bcs plb_end ; Equiv to bra
|
|
plb_nochar
|
|
clc
|
|
plb_end
|
|
cli ; Enable IRQ
|
|
rts
|
|
|
|
check_buffer
|
|
lda charcount
|
|
rts
|