diff options
| author | B. Watson <urchlay@slackware.uk> | 2022-10-25 02:29:09 -0400 |
|---|---|---|
| committer | B. Watson <urchlay@slackware.uk> | 2022-10-25 02:29:09 -0400 |
| commit | f1c630523239c550dc920eb14ab4652da7ca4343 (patch) | |
| tree | 28a5fe7038bff3a06040350c3fc5e485df95ff1c | |
| parent | aea79e6aaf2cf9790c8cc07c7d8aba3c85aa7819 (diff) | |
| download | dla-asm-f1c630523239c550dc920eb14ab4652da7ca4343.tar.gz | |
Fix PAL/NTSC divisor
| -rw-r--r-- | dla.s | 39 |
1 files changed, 24 insertions, 15 deletions
@@ -239,11 +239,11 @@ main_done: ; print menu ldx #menulen -blloop: +menuloop: lda menumsg,x sta textbuf,x dex - bpl blloop + bpl menuloop ; calculate and print elapsed time in minutes. our only use of ; the floating point ROM routines. @@ -268,28 +268,40 @@ blloop: sta FR0 jsr IFP ; ...ok, now: jsr FADD ; add the high bytes in jiffies, result in FR0 again + ; we now have the 3-byte jiffy count in FR0. - ; 3600 NTSC jiffies = 1 minute, so divide. - ldx #<fp3600 - ldy #>fp3600 - jsr FLD1R ; FR1 = 3600.0 - lda PAL ; are we on a PAL Atari? + ; 3600 NTSC jiffies or 3000 PAL jiffies = 1 minute, so divide. + ; floating point constants: + ; 3600.0 is $41,$36,$00,$00,$00,$00 + ; 3000.0 is $41,$30,$00,$00,$00,$00 + lda #$41 ; excess-64 base-100 exponent and sign (bit 7 = 0 means positive) + sta FR1 + ldx #$36 ; NTSC + lda PAL and #$0e - bne ntsc ; no, use constant as-is - lda #$30 ; yes, adjust (3000 PAL jiffies/sec) - sta FR0+1 + bne ntsc + ldx #$30 ; PAL ntsc: + stx FR1+1 + lda #0 + sta FR1+2 + sta FR1+3 + sta FR1+4 + sta FR1+5 jsr FDIV ; FR0 = FR0 / FR1 jsr FASC ; render as ASCII + ; Now clean up the output from FASC and copy it to our menu line. ; FASC puts its results at LBUFF ($0580, aka linebuf). ; Unfortunately it can have a leading zero, and the last ; digit has the high bit set (as a terminator). We want only ; 6 characters including the decimal point, which could be e.g. - ; 1.2345 12.345 123.45 1234.5 + ; 0.1234 (the 0 will show as a space) or 1.2345 12.345 123.45 1234.5 + ; Really elegant software would print this as minutes and seconds, + ; with tenths of seconds, e.g. 1:23.4. Not that worried about it though. ldx #$ff lda linebuf - cmp #'0' ; skip the leading zero if present + cmp #'0' ; skip the leading zero if present (a space will be seen in its place) bne ascloop inx ascloop: @@ -346,9 +358,6 @@ hang: jmp hang ; TODO: code to save image goes here. ;;; End of main() - ; floating point constant 3600.0 -fp3600: .byte $41,$36,$00,$00,$00,$00 - ; screen codes for menu menumsg: .byte $00,$00,$00 ; 3 digits of minutes |