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[rtl] Bugreport & Bugfix: screen blanking with RTL2.0
Hi!
With the rather timing critical pwm-demos (see my previsious mail),
i have discovered a strange effect, using an Athlon 600 MHz and a
PentiumII/333 (within a Notebook) running RTL2.0:
When logged in (in graphical mode / X-Server), the screen-saver
is activated, although it is set to 10 minutes, and i have just
typed something or moved the mouse.
Additionaly, some running "xanim" and "xquake" were stopped randomly
(experienced that only with the notebook, but who knows ...)
The screen-sever problem also appeard in an early RTAI-version (0.2).
Since RTL and RTAI have basicaly the same architecture, i assumed the
same bug.
I met Paolo Montegazza in Vienna at the Linux Real-Time Workshop.
He told me, that he had solved that problem some time ago, and he
showed me, what he has altered to make the effect going away: in
an RTL2.0-patched kernel-2.2.13 in file
/usr/src/linux/arch/i386/kernel/time.c
in function
static void timer_interrupt()
you have to comment the following equation (line 456):
delay_at_last_interrupt = (count + LATCH/2) / LATCH;
I didn't dig deeper, but i assume, this is some sort of
optimization, that is corrupted/disturbed by RT-Linux (early
RTAI as well).
Now, everything seems to work just fine: i didn't discovered
the undesired screen-blanking any more, and the apps (xanim/xquake)
on the notebook are also working without stopping randomly for
several hours (usuals, the effect showed up within 20 minutes).
comments?
Bernhard Kuhn
P.S.: Many thanks to Paolo Montegazza, who showed my solution!
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