Date: Mon, 28 Sep 1998 10:06:33 -0600 From: Nate Williams <nate@mt.sri.com> To: Bruce Evans <bde@zeta.org.au> Cc: nate@mt.sri.com, tlambert@primenet.com, current@FreeBSD.ORG, yokota@zodiac.mech.utsunomiya-u.ac.jp Subject: Re: VM86 and APM Message-ID: <199809281606.KAA17209@mt.sri.com> In-Reply-To: <199809280444.OAA10819@godzilla.zeta.org.au> References: <199809280444.OAA10819@godzilla.zeta.org.au>
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> >> > Does anybody know of any problem using VM86 and the apm driver together? ... > Actually, having APM disabled doesn't mean that it is disabled , except > possibly when VM86 is configured, since apm_setup() is called from > locore.s without looking at the `disabled' flag. Umm, all of this is true (if irrelevant). The original response made the claim that *IF* the APM was disabled in BIOS, we would would find it with the old code but not with the new code. But, if it's disabled from the BIOS (not from UserConfig), then things can act differently. > The disabled flag isn't > really valid at that time since it might be changed in Userconfig. > Calling apm_setup() is not a no-op since it sets `apm_version' > which clock.c uses to decide whether the TSC timecounter can be used. It only sets apm_version *IF* the APM BIOS is found. However, the original poster mentioned that his APM BIOS can't be found, not that he has 'less than perfect' clocks. > Misconfigured systems (with apm configured but disabled) always get the > i8254 timecounter which seems to be buggier than the TSC timecounter. Actually, my older FreeBSD systems that use the i8254 are *much* more accurate than the newer systems that use the Pentium counters and such. (Verified using XNTPD.) But, one person's experience doesn't make it a fact, just a statistic. :) Also, apm configured/disabled system don't necessary use the i8254 timecounter unless they use the APM_BROKEN_STATCLOCK option (which is turned on by default, but is not a requirement.) However, Bruce is correct that *IF* the APM BIOS is both configured in the BIOS *AND* disabled in UserConfig then some of the side-effects ares not completely disabled in FreeBSD. Nate To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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