From mboxrd@z Thu Jan 1 00:00:00 1970 From: khali@linux-fr.org (Jean Delvare) Date: Sun, 04 Jun 2006 17:56:21 +0000 Subject: [lm-sensors] sysfs interface for fan present capability Message-Id: <20060604195621.b5ae7692.khali@linux-fr.org> List-Id: References: <4482843D.5020506@hhs.nl> In-Reply-To: <4482843D.5020506@hhs.nl> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lm-sensors@vger.kernel.org > On Sun, 04 Jun 2006, Hans de Goede wrote: > > I think they are just seeing if it gives any "ticks" at all, so it won't > > detect a 2 wire fan even if connected to one if its headers. > > Two-wire fans can be detected just as well as three-wire ones, if you > measure current draw :) In fact, some chips (like the lm75) can actually > COUNT ticks on two-wire fans by measuring spikes in the current draw... Definitely not the LM75, as it is a temperature-only sensor chip. But I remember reading datasheets mentioning tick count on 2-wires fans, indeed. Strangely enough, some vendors are doing the opposite and propose 4-wire fans, the idea being that tick counts tend to be lost when fan speed control is in use on 3-wire fans. > If you detect fan presence using ticks, you will never detect a stuck fan on > startup, which is *dangerous* as it could cause the software inhibit an > alarm on that fan. Indeed - which is why I don't want us to emulate it in software. -- Jean Delvare