kern/112544: [acpi] [patch] Add High Precision Event Timer Driver for userland timer facility

[Mark Linimon]

The following reply was made to PR kern/112544; it has been noted by GNATS.

From: linimon at lonesome.com (Mark Linimon)
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: kern/112544: [acpi] [patch] Add High Precision Event Timer Driver for userland timer facility
Date: Fri, 29 Feb 2008 19:41:46 -0600

 ----- Forwarded message from John Baldwin <jhb at freebsd.org> -----
 
 The HPET contains multiple bits.  One is a general count down timer that we 
 use for timekeeping.  In addition it contains a variable number of comparator 
 registers each of which can be used to generate interrupts at varying 
 frequencies (or one-shot interrupts, etc.).  The current in-kernel HPET 
 support only handles the count down timer.  We do not have any support for 
 the comparators.  The code in the PR does include support for the 
 comparators.  However, it's aim is to export them for use by userland 
 drivers.  FreeBSD will probably end up using the HPET comparators to back 
 deadline-style clock interrupts in place of the RTC or lapic timer at some 
 point in which case certain pieces of this code may be useful.
 
 The commit I made just extracted a few of the changes in the original patch, 
 it did not contain all of the changes in the patch.  It is probably best to 
 mark this as suspended and leave it as freebsd-acpi@ for now as I'm not 
 currently planning on doing the deadline clock stuff.
 
 -- 
 John Baldwin
 
 ----- End forwarded message -----