10 REM >Y2KFixS
   20 REM by Steven Flintham
   30 REM
   40 REM Version 0.01
   50 REM
   60 REM Friday 25th July 1997
   70 REM Thursday 21st August 1997
   80 :
   90 REM This is a bit of a bodge, but should suffice. The Master Reference
  100 REM Manual implies that the RTC itself contains a century number and
  110 REM correctly handles the 21st century. Whether or not this is actually
  120 REM the case, I don't want to get involved in talking directly to the
  130 REM RTC - I'd probably have to disassemble the OS to find out how to
  140 REM do it and there's always a slight risk of doing something nasty to
  150 REM the chip.
  160 REM
  170 REM All I do is provide a "front end" to the OSWORD calls, changing the
  180 REM "19" in the date string to "20" for years from 0 to 69 inclusive -
  190 REM this adjusts the range of years which is displayed correctly to
  200 REM 1970-2069. This works because the RTC doesn't know 1900 wasn't a
  210 REM leap year. The OSWORD call to read the CMOS clock in BCD format is
  220 REM unmodified as it doesn't return a year; anything using it for
  230 REM display purposes probably assumes a 19XX year, but there's nothing
  240 REM I can do about that.
  250 REM
  260 REM There's no need to do anything about setting the RTC; the OS treats
  270 REM a 20XX year as a 19XX year for this purpose, which is just what's
  280 REM wanted with this fix.
  290 :
  300 PROCinit
  310 PROCassemble
  320 OSCLI "Save Y2KFix "+STR$~code%+" "+STR$~(save_to_here-dest%+code%)+" "+STR$~redirect_wordv+" "+STR$~dest%
  330 END
  340 :
  350 DEF PROCinit
  360 DIM code% 1024
  370 dest%=&A80
  380 :
  390 wordv=&20C
  400 osword=&FFF1
  410 :
  420 REM I can't see why I shouldn't use these locations for this purpose
  430 REM although in theory it might cause problems.
  440 osword_x=&F0
  450 osword_y=&F1
  460 ENDPROC
  470 :
  480 DEF PROCassemble
  490 FOR opt%=4 TO 7 STEP 3
  500 P%=dest%:O%=code%
  510 [OPT opt%
  520 \ This isn't needed once it's been executed the first time, so it can
  530 \ be overwritten after loading. Depending on where the fix code is
  540 \ placed in memory, it might be more useful to have this once-only
  550 \ code at the end instead of the beginning. (It would then be necessary
  560 \ to save the uninitialised data though.)
  570 .redirect_wordv
  580 LDA wordv:CMP #my_osword MOD 256:BNE redirect_vector_do_it
  590 LDA wordv+1:CMP #my_osword DIV 256:BEQ rts \ Already redirected
  600 .redirect_vector_do_it \ Actually redirect the vector
  610 LDA wordv:STA old_vector
  620 LDA wordv+1:STA old_vector+1
  630 LDA #my_osword MOD 256:STA wordv
  640 LDA #my_osword DIV 256:STA wordv+1
  650 .rts
  660 RTS
  670 :
  680 \ TODO?; I don't preserve the processor flags at all; is this a flaw?
  690 .my_osword
  700 CMP #14:BNE pass_on \ Only process calls to read the clock
  710 STX osword_x:STY osword_y
  720 LDY #0:LDA (osword_x),Y
  730 CMP #1:BEQ restore_pass_on \ nothing to change for BCD read
  740 \ Handle the string operations by letting the OS deal with it, then
  750 \ modifying the century in the string if appropriate
  760 TXA:PHA:LDA osword_y:PHA
  770 TAY:LDA #14:JSR old_osword \ X hasn't been modified
  780 PLA:STA osword_y:PLA:STA osword_x
  790 \ Year within century is at offsets 13 and 14
  800 LDY #13:LDA (osword_x),Y
  810 SEC:SBC #ASC"0"
  820 ASL A:STA year_within_century
  830 ASL A:ASL A
  840 \ The carry should be clear anyway, but it seems silly to risk problems.
  850 CLC:ADC year_within_century:STA year_within_century
  860 \ year_within_century now contains C*10, where the year is ABCD
  870 INY:LDA (osword_x),Y:SEC:SBC #ASC"0"
  880 CLC:ADC year_within_century
  890 \ A now contains CD, where the year is ABCD
  900 CMP #70:BCS claim \ If CD>=70, do nothing
  910 LDY #11:LDA #ASC"2":STA (osword_x),Y
  920 INY:LDA #ASC"0":STA (osword_x),Y
  930 .claim
  940 \ Y has been corrupted, but OS 3.2 (at least) doesn't preserve either
  950 \ X or Y (it will have corrupted X itself on the earlier OSWORD call
  960 \ but this code hasn't corrupted it). It does preserve A, however.
  970 LDA #14
  980 RTS
  990 .restore_pass_on
 1000 LDA #14:LDY osword_y \ X hasn't been modified
 1010 .old_osword
 1020 .pass_on
 1030 JMP (old_vector)
 1040 :
 1050 .save_to_here
 1060 \ Uninitialised data
 1070 .old_vector EQUW 0
 1080 .year_within_century EQUB 0
 1090 ]
 1100 NEXT
 1110 ENDPROC