mirror of
https://github.com/uffejakobsen/acme.git
synced 2024-12-11 20:49:23 +00:00
dac562b84f
git-svn-id: https://svn.code.sf.net/p/acme-crossass/code-0/trunk@323 4df02467-bbd4-4a76-a152-e7ce94205b78
87 lines
2.4 KiB
Plaintext
87 lines
2.4 KiB
Plaintext
;ACME 0.97
|
|
|
|
; here's an implementation of the "double dabble" algorithm, a quick
|
|
; and easy way to output integers as decimal digits.
|
|
|
|
; in this example, the 24-bit value of the time variable TI is shown
|
|
; on the screen as eight decimal digits, updated once per frame (every
|
|
; once in a while there will be a glitch because the system interrupt
|
|
; handler is not synchronized with the screen, to fix this is left as
|
|
; an excercise to the reader).
|
|
; the raster time used is indicated via changes of the border color.
|
|
|
|
DIGITS = 8 ; three input bytes -> 24 bits -> max 16777215 -> we need eight digits
|
|
!addr {
|
|
ti_high = $a0 ; input data
|
|
ti_med = $a1
|
|
ti_low = $a2
|
|
byte = $fb ; buffers input byte during shifts
|
|
out = $0400 ; where to show output digits (big-endian!)
|
|
raster = $d012 ; to sync with screen
|
|
border = $d020 ; to show raster time
|
|
}
|
|
* = $0801
|
|
!src "misc/basicstub.a"
|
|
--- ; wait for lower border
|
|
lda raster
|
|
cmp #251
|
|
bne ---
|
|
inc border ; start "stop watch"
|
|
jsr dd_clear ; clear output
|
|
sei ; make sure TI is stable while we read it
|
|
lda ti_low
|
|
pha
|
|
lda ti_med
|
|
pha
|
|
lda ti_high
|
|
cli ; re-allow irq
|
|
jsr dd_process_A ; process high byte
|
|
pla ; process medium byte
|
|
jsr dd_process_A
|
|
pla ; process low byte
|
|
jsr dd_process_A
|
|
jsr dd_result ; convert result from 0..9 values to '0'..'9' characters
|
|
dec border ; stop "stop watch"
|
|
jmp ---
|
|
|
|
dd_clear ; clear result bytes
|
|
ldx #DIGITS - 1
|
|
lda #0
|
|
--- sta out, x
|
|
dex
|
|
bpl ---
|
|
rts
|
|
|
|
dd_result ; convert result bytes to ascii digits
|
|
ldx #DIGITS - 1
|
|
--- lda out, x
|
|
ora #$30
|
|
sta out, x
|
|
dex
|
|
bpl ---
|
|
rts
|
|
|
|
dd_process_A ; process eight bits
|
|
; use the zero-means-empty trick so we do not need a bit counter:
|
|
sec ; create "marker bit"
|
|
rol ; push into A, now C = data bit
|
|
sta byte ; remember for later
|
|
; here's how to process a bit:
|
|
; "out" holds digits (0..9, not '0'..'9'),
|
|
; but in big-endian order (for screen output).
|
|
; the new bit is in C:
|
|
next_bit ldx #DIGITS - 1 ; loop over output digits
|
|
next_digit ldy out, x ; now Y = 0..9 (old value)
|
|
lda table, y ; now A = 0/1/2/3/4/128/129/130/131/132
|
|
rol ; now A = 0..9 (new value), bit for next digit in C
|
|
sta out, x ; update digit
|
|
dex
|
|
bpl next_digit
|
|
;clc ; only needed if overflow possible
|
|
rol byte ; get next data bit
|
|
bne next_bit
|
|
; byte is empty (C is 1, but that's the marker bit)
|
|
rts
|
|
table
|
|
!by 0, 1, 2, 3, 4, $80, $81, $82, $83, $84
|