[haiku-bugs] Re: [Haiku] #8533: S-ATA and AHCI boot problem
- From: "tqh" <trac@xxxxxxxxxxxx>
- Date: Sun, 09 Sep 2012 10:39:43 -0000
#8533: S-ATA and AHCI boot problem
----------------------------+-----------------------------
Reporter: Morbid | Owner: marcusoverhagen
Type: bug | Status: new
Priority: normal | Milestone: R1
Component: Drivers/Disk | Version: R1/Development
Resolution: | Keywords:
Blocked By: | Blocking: 7665, 8953
Has a Patch: 0 | Platform: All
----------------------------+-----------------------------
Comment (by tqh):
Someone reported it working when disabling HPET in BIOS. Might be related
to the problems mentioned here perhaps?
http://en.wikipedia.org/wiki/High_Precision_Event_Timer
HPET is a continuously running timer that counts upward, not a one-shot
device that counts down to zero, causes one interrupt and then stops.
Since HPET compares the actual timer value and the programmed target value
on equality rather than "greater or equal", interrupts can be missed if
the target time has already passed when the comparator value is written
into the chip's register. In the presence of non-maskable interrupts (such
as System Management Interrupts) that do not have a hard upper bound on
their execution time, this race condition requires time-consuming re-
checks of the timer after setup and is hard to avoid completely. The
difficulties are exacerbated if the comparator value is not synchronized
with the timer immediately, but delayed by one or two ticks, as some
chipsets do.
--
Ticket URL: <http://dev.haiku-os.org/ticket/8533#comment:4>
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