Hi everybody,
I have been thinking about the issue described in bug 1748:
freedos.sourceforge.net/bugzilla/cgi-bin/show_bug.cgi?id=1748
On some embedded systems, when you set the date to >= 2000 with
DOS and reboot, DOS will report a date of 1980. My theory is that
this is because that embedded system BIOS fails to really store
the century first, and FreeDOS CLIPS "1901" to 1980 while other
DOSes like DR DOS and MS DOS might just ignore the century and
WRAP "1901" into 2001 which is the date the user tried to set.
While RBIL gives evidence that DOS could even hook BIOS int 1a
to fix y2k issues in a "lowlevel" way, I suggest that FreeDOS
should only have a fix inside DOS itself, without hooking yet
another BIOS interrupt. See: kernel/initclk.c drivers/*clk.asm
kernel/sysclk.c and kernel/systime.c ... Init_clk_driver will
call int 1a.2 and 1a.4 and then call int 21.2b. SUGGESTION:
Add "fold 1900-1979 to 2000-2079 before callint int 21.2b" in
initclk.c (note that DOS date keeping uses DaysSinceEpoch as
set via int 21, initially by Init_clk_driver, so the date is
fetched from the BIOS once at boot time, not later...!)
Index: kernel/initclk.c
===================================================================
--- kernel/initclk.c (revision 1354)
+++ kernel/initclk.c (working copy)
@@ -58,6 +58,8 @@
dosregs.a.b.h = 0x2b;
dosregs.c.x = 100 * InitBcdToByte(regsD.c.b.h) /* century */
+ InitBcdToByte(regsD.c.b.l);/* year */
+ /* A BIOS with y2k (year 2000) bug will always report year 19nn */
+ if ((dosregs.c.x >= 1900) && (dosregs.c.x < 1980)) dosregs.c.x += 100;
dosregs.d.b.h = InitBcdToByte(regsD.d.b.h); /* month */
dosregs.d.b.l = InitBcdToByte(regsD.d.b.l); /* day */
init_call_intr(0x21, &dosregs);
Are there any objections against that initclk.c modification?
Bonus QUESTION: Why is YearsSince1980 and daysSince1980 never
modified? See kernel.asm, it is stuck to 0 and -1. The whole
area of date related things in the SDA seems to be dummy...??
( CALL int 1ah, ah=4, carry cleared in case BIOS leaves carry
unchanged will RETURN carry cleared if okay and the BCD
encoded date as century CH, year CL, month DH and day DL... )
RBIL has several interesting notes about int 1a.4:
START RBIL NOTES
Notes: DR-DOS 7.02 (after 1998-06-06) and 7.03 hook this function and
correct the century to 20xx if the reported year is 1900..1980 to auto-fix
ROM-BIOSes which are not Year 2000 compliant. On a running system,
it would also correct the rollover bug from 1999/12/31 to 2000/01/01.
The latter can be turned off using the new CONFIG.SYS YEAR2000=ON|OFF
command, as hooking INT 1Ah can sometimes cause compatibility
problems with 3rd party software...
Using EXCLUDESTEALTHINT=1A, though, will allow QEMM's Stealth
features to coexist with the DR-DOS Year 2000 rollover support...
PC DOS 7 plus Y2K fixes and PC DOS 2000 provide similar, though
not identical means, which cannot be switched off.
MS-DOS and older issues of PC DOS do not provide any such means, and
thus requires extra Y2K-TSRs to be loaded when run on buggy BIOSes...
END RBIL NOTES
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