From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <445ED191.2070401@domain.hid> Date: Mon, 08 May 2006 01:05:21 -0400 From: Jim Cromie MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Xenomai-help] FYI - SMM interrupts and latency. List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "xenomai@xenomai.org" found this relevant quote o NTP pages. It agrees with what we already know / have been told *8.3.1.2.1. *How can SMM affect Interrupt Processing? * *Let me quote an explanation written by Poul-Henning Kamp from the newsgroup: I was gathering some data for Professor David L. Mills today and they looked lousy to put it mildly, every 300-400 seconds I had a 40-50 microsecond peak in my data. After some debugging I know know what it was: The SMM mode interrupts to the BIOS. This machine is brand new, and I had never put a PPS signal on it before, it uses the PIIX4 chip from Intel and appearantly the SMM BIOS gets called at regular (but not very precise) intervals to monitor temperatures and fans and whats not. Needless to say, this could not be disabled in the BIOS setup. I found out I could disable the SMI output from the PIIX4 to the CPU by clearing bit zero in the GLBCTL register in the third function of the 82371AB chip. You need to find the IO base address from register 0x40 in the PCI header, and add the 0x28 to that address. For my motherboard that ended up being 0xe428, your milage will vary, and you should Do The Right Thing to find this location. Needless to say, the SMM BIOS will not be able to check if your CPU is able to make toast on if you disable it this way, so you'd better know what you're doing.