Date: Thu, 19 Apr 2001 22:59:45 -0600 From: Warner Losh <imp@harmony.village.org> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: David Miller <dmiller@sparks.net>, freebsd-hackers@FreeBSD.ORG Subject: Re: [OT] parallel port for IO? Message-ID: <200104200459.f3K4xj809936@harmony.village.org> In-Reply-To: Your message of "Thu, 19 Apr 2001 22:02:48 %2B0200." <60866.987710568@critter> References: <60866.987710568@critter>
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In message <60866.987710568@critter> Poul-Henning Kamp writes: : The BIOS misuse of SMM mode can give you jitter in the 1msec range : and there is not much you can do about it. I found out when I : clocked a motherboard with a 14.318 derived from a Rb, and timed : 1Hz pulses derived from a Cs. Every 400 seconds I ran into the : SMM interrupt for about 10 seconds, and all my measurements were : late by 800-900 microseconds :-( : : Intel doesn't care much for precision timing... Agreed. SMM wasn't turned on on this machine. But there was a disk drive that every so often would hammer as a different application would core dump. During the core dump, interrupt latency went way up for reasons I don't understand. The CPU was a tiny 486 133MHz underclocked to 100MHz for cooling. The pentium systems were much better about this. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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