Date: Fri, 20 Apr 2001 06:49:07 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Warner Losh <imp@harmony.village.org> Cc: David Miller <dmiller@sparks.net>, freebsd-hackers@FreeBSD.ORG Subject: Re: [OT] parallel port for IO? Message-ID: <66167.987742147@critter> In-Reply-To: Your message of "Thu, 19 Apr 2001 22:59:45 MDT." <200104200459.f3K4xj809936@harmony.village.org>
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In message <200104200459.f3K4xj809936@harmony.village.org>, Warner Losh writes: >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. Then the disk is probably running in PIO mode which thrashes your interrrupts. >The pentium systems were much better about this. Probably because it ran DMA... -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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