Problems with hwclock

2008-11-03T20:14:33Z

StephenKell: My T22 and A22m (now stolen )-: also suffer from this

This page discusses the problem with /dev/rtc on certain models.

== Problem description ==
On bootup,a message like this shows up:

<pre>select() to /dev/rtc to wait for clock tick timed out</pre>

The RTC kernel driver can't handle the system clock.

== Possible solutions ==

=== Using the --directisa switch of hwclock(8) ===
The '''hwclock''' command knows the parameter ''--directisa'' to access the system clock "directly" instead of accessing it by using /dev/rtc. There are several ways of doing this automatically.

==== Generic instructions ====
Move /sbin/hwclock (or wherever it is located on your system) to '''/sbin/hwclock.dist''' and create the following shell script, which you place at /sbin/hwclock

<pre>#!/bin/sh
/sbin/hwclock.dist --directisa "$@"</pre>
Make the script executable (apply the same permissions you had for ''hwclock'' before) and keep your packaging system from overwriting it on updates.

==== Debian 4.0 (etch) ====
Add the following to '''/etc/default/rcS''':

<pre>HWCLOCKPARS="--directisa"</pre>

==== Debian 3.1 (sarge) and previous ====
Edit '''/etc/init.d/hwclock.sh''' and change all instances of "/sbin/hwclock" to "/sbin/hwclock --directisa".

==== Gentoo ====
Edit '''/etc/conf.d/clock''' and set ''CLOCK_OPTS'' to
<pre>CLOCK_OPTS="--directisa"</pre>

=== Compiling RTC-support into the kernel instead of as a module ===

Compiling RTC-support {{kernelconf|CONFIG_RTC||||||}} into the kernel instead of compiling it as a module seems to work also. Tested on: 2.6.20.6 at Thinkpad {{Z61m}} 9450-3HG

=== Using Alternate RTC Drivers ===

Use of an alternate RTC driver may yield better results. RTC drivers available in recent kernels include:
* '''genrtc''' {{kernelconf|CONFIG_GEN_RTC||||||}}: A generic RTC emulation driver.
* '''rtc class''' {{kernelconf|CONFIG_RTC_CLASS||||||}}: A new RTC driver class which separates the userspace interface from the hardware-level drivers. Several user-level interfaces may be exposed, including the venerable /dev/rtc node, independently of the actual underlying hardware. These drivers are marked experimental as of kernel 2.6.21.

Strictly speaking, for the new RTC class drivers, you need to load a user-level interface driver as well as a hardware driver, making these drivers more complex to use. However, in many cases, loading just the user-level interface driver rtc_dev is sufficient to get hwclock working.

All RTC drivers may be compiled as loadable modules. To test which driver works best for you, load each driver in turn and use hwclock to test results. Example:

<pre># modprobe rtc
# hwclock --show
# rmmod rtc
# modprobe genrtc
# hwclock --show
# rmmod genrtc
# modprobe rtc_dev
# hwclock --show
# rmmod rtc_dev</pre>

== Affected Models ==

*Thinkpad {{T60}} (not all models)
*Thinkpad {{T61}} (type 7662, maybe others)
*Thinkpad {{T60p}}
*Thinkpad {{X60s}}
*Thinkpad {{X61s}}
*Thinkpad {{Z61m}}
*Thinkpad {{Z61t}} (type 9440-CTO, maybe others)
*Thinkpad {{R60e}} (type 0657, maybe others)
*Thinkpad {{T22}} (type 2647, maybe others)
*Thinkpad {{T42}} (type 2373, maybe others)
*Thinkpad {{R52}} (type 1846)
*Thinkpad {{R61}} {type 8944, maybe others}
*Thinkpad {{A22m}}

Note: Also affects Compaq Presario C300

== Affected Operating Systems ==

*Linux, all flavours. Tested with kernel 2.6.18, 2.6.19, 2.6.20.6, 2.6.21.1, 2.6.22.5

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Problems with hwclock