> > > I thought SMI was supposed to increase latencies, but I only see
> > > latencies < 60us at any load, unless I start video capture. Does
> > > the latency test absolutely rule out SMI as the cause?
> >
> > Not really, e.g. if the video capture device is USB-attached, then
> > SMI could possibly remain in the picture.
>
> I have used the bttv driver with xawtv or mythtv and nvidia
> proprietary drivers on a dual pIII machine running latency and the
> maximum latency was far less than 100 us. What produces large spots,
> however, is switching virtual terminals or changing resolution.
> Doesn't xawtv change resolution for full screen mode ? Did not you use
> the 768x576 modeline hack ?
The video capture is not USB, it's a PCI card. Since I don't see poor
latencies I'm guessing my problem is *not* SMI related.
> > Is there any way to
> > > check whether SMI is actually disabled?
> > >
> >
> > Gilles will likely have more clue here, but I guess that reading
> > back the state of the GBL_SMI_EN_BIT from the SMI's MMIO space
> > would probably tell us if a previous request to disable SMI
> > globally did succeed or not. The code in question is in
> > ksrc/arch/i386/smi.c.
>
> That is a good idea. Another idea would also be to read the state of
> the lock bit (named SMI_LOCK).
At boot GEN_PMCON_1 = 0x0220. Bit 4 is SMI_LOCK, which is zero, so I
should be allowed to disable SMI. This was read using the following
code, which I hope is correct:
u_int8_t hi, lo;
int gen_pmcon_1;
pci_read_config_byte(smi_dev, 0xA0, &lo);
pci_read_config_byte(smi_dev, 0xA1, &hi);
gen_pmcon_1 = ((int)hi<<8) | lo;
Further, reading SMI_CTRL_ADDR at boot:
- before clearing GBL_SMI_EN_BIT -> 0x0000203B
- after clearing GBL_SMI_EN_BIT -> 0x0000203A
GBL_SMI_EN_BIT is bit zero, which is reported as cleared i.e. SMI
is disabled.
If there are no further ideas on how to fix this, I would be interested
in hearing from people about the PC's that you use that are know to work
well with Xenomai. I'd be looking for a fast new desktop PC. Is AMD a
better bet? I deliberately avoided AMD when purchasing this new Intel PC
(the I/O controller is ICH6) since new AMD PC's have always given me
trouble with I/O controller drivers lagging behind hardware changes. Any
suggestions much appreciated.
Saul.
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