[mythtv-users] 0.19, XvMC, and Prebuffer pause

Joe Silver devils.taco at gmail.com
Wed Mar 1 22:20:44 UTC 2006


On 3/1/06, Brian Wood <beww at beww.org> wrote:
>
>
>
> On Mar 1, 2006, at 1:42 PM, Dylan R. Semler wrote:
>
> > <http://www.mythtv.org/wiki/index.php/PCI_Latency>
> >
> >>> I found my IDE controller latency was set to zero, so I reset it to
> >>> 32 (20hex).  I'm not at home to try playback right now, but I was
> >>> wondering what others who are having this problem find for their
> >>> IDE/SATA controller latency.  Maybe this could fix us up?!?!  I'll
> >>> report back later tonight what I find out.
> >>>
> >>
> >> So far, with a very limited number of samples, the people who have
> >> found their disk controllers set to zero have either been unable to
> >> reset the latency value, or have not seen any positive results from
> >> doing so.
> >>
> >> Only the machines which have drive controller latency set to 32 or 64
> >> initially have had much luck in adjusting them.
> >>
> >> Again, this is from a *very* limited number of samples (6 to be
> >> exact)
> >> so please report your results, positive or negative, as well as the
> >> chipset your mobo is using (perhaps on the WiKi page ??)
> >
> > I just tried changing the latency on my three machines.  I have two
> > Dell
> > 8200 desktops from about 2002 and a Sager laptop from December
> > 2005.  In
> > all three machines, the initial IDE latency was 0 and changing it with
> >
> > setpci -v -s 00:1f.1 latency_timer=b0 (or any other value)
> >
> > did not seem to do anything.  At least lspci -v continued to display
> > their latency as 0 (I have not been able to test this with Myth yet).
> > Furthermore, I found that if tried this command on ANY controller
> > whose
> > intial latency was 0, the command did nothing.  If the initial latency
> > was not zero, the command would change the latency to the desired
> > value.  I Also tested that if a controller ititially had a non-zero
> > latency, and I changed it to zero, I was still able to change it
> > back to
> > other values.  I have no idea why this is or what can be done, but I
> > thought I'd add some more datapoints to the set.  If anyone wants the
> > maker of these mobos, I can probably find that out somehow.
> >
>
> That matches out what I have recorded. The one incident of somebody
> setting a zero latency to something else could not be repeated and I
> take it as bad data.
>
> I think by spec latency does not have to be settable unless the
> device is capable of bus mastering and bursting two or more shots
> over the bus, but I can't imagine a drive controller that wouldn't
> want to be able to do that. The latency might just be fixed at some
> unknown value and not readable by lspci for some reason.
>


Maybe I'm an exception to the rule, but setpci lets me adjust the latency of
the IDE controller, and checking again afterwards with lspci -v seems to
indicate the change has held:

00:14.1 IDE interface: ATI Technologies Inc: Unknown device 4349 (prog-if 8a
[Master SecP PriP])
        Subsystem: ATI Technologies Inc: Unknown device 4349
        Flags: bus master, medium devsel, latency 32
        I/O ports at <ignored>
        I/O ports at <ignored>
        I/O ports at <ignored>
        I/O ports at <ignored>
        I/O ports at ff00 [size=16]



however, the ISA bridge also has a latency of 0 and that doesn't change
after setting with setpci:

00:14.3 ISA bridge: ATI Technologies Inc: Unknown device 434c
        Subsystem: ATI Technologies Inc: Unknown device 434c
        Flags: bus master, 66Mhz, medium devsel, latency 0
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