[linux-audio-user] Tracking down overruns

Mark Knecht markknecht at comcast.net
Sun Sep 14 17:11:00 EDT 2003

On Sat, 2003-09-13 at 18:47, Benji Flaming wrote:
> I'm glad to meet you.  I've been playing with Pro Tools since 4.3.1, and my
> studio is running currently running MIX plus on an old beige G3/300 running
> MacOS 9.  I've often wanted to migrate over to Windows, but we'd lose all of
> our plug-ins.  

PTLE for me. Thought about an 002 and decided before I jumped I'd give
Linux a try.

> Pro Tools is actually one of my biggest motives for moving to
> Linux - one gets tired of jumping through flaming hoops every time
> DigiDesign or Apple release new hardware or software.

Absolutely. I need to go to Guitar Center an buy my latest 6.01 upgrade
if I want to stay on the treadmill.

> > Forgiven. No problem. However, this means you are doing latency testing
> > to your system drive. Is this correct? You do not have a second,
> > separate audio drive at this point? I ask as I notice you have the
> > Promise ATA controller on IRQ11.
> Well...I *do* have a third drive hooked up to the Promise controller, but
> upon installing it, I discovered that my power supply doesn't want to supply
> power to another drive - even though I have enough power hookups.  I can
> only use the drive if I disconnect power from my LS120, CD-ROM or Windows
> hard drive.  Time to buy a new power supply....

Yep, this is a problem. My solution was to use a 1394 drive for my audio
drive, both under Pro Tools (Win XP) and Linux. It then doubles as a
simple way to get data between boxes if I don't want to spend time
messign with getting Samba working...

> I'm running Blackbox - we seem to be cousins.

Once again yes...

> For what it's worth, I've also posted my XF86Config:
> http://www.comevisit.com/NorthernSunrise/latency/XF86Config
> It has a few things I need to fix, but nothing that I think would affect
> audio performance.

I'm terrible at kernel configuration, so I hope someone else will help
more with this part.

> My machine is absolutely adamant that the sound card *has* to go there :(  I
> spent many frustrating and fruitless hours trying to address this issue.  I
> sifted through every single BIOS setting, juggled the cards all over the
> place, but the only way I could get the card off IRQ 5 was by disabling that
> IRQ.  When I did this, it moved the card up to IRQ 4, and so on.  In short,
> my machine *always* gives the sound card the lowest-priority IRQ, and
> provides no way (that I could find) to assign IRQs manually.  Ultimately, I
> put things back as they were, and decided to be more careful next time I buy
> a board.

OK, I certainly get how this has happened, but I eventually tricked my
Dell P3 500 box that runs GigaStudio into playing nice. It was no fun
though. Here's the short version of the story...

1) There are two ways IRQs get assigned, both depending on BIOS:
a) BIOS gives you an option to set an IRQ on a per PCI slot basis
b) BIOS jest sets them.

2) My P3-500 (which sounds like your machine) just assigned specific
IRQs to specific slots. In this case I had to look at what cards were
getting what IRQs and then rearrange cards to get the IRQ.

3) In your case I see the eth0 has IRQ11 which is a good IRQ. I looked
at the IWill page but was unclear if the Ethernet controller is on the
motherboard or a PCI card. If it's a PCI card, then the way I handled my
Dell was to remove EVERY card except the VGA adapter and then put one
card in at a time, see what interrupt BIOS gave it, decide what card I
wanted to have that interrupt, put that card in and move on to the next
card. It meant a number of boot cycles, but now the machine has run for
18 months with a AudioPhile 2496 and an RME HAmmerfall Light and a 1394
adapter and an Ethernet controller and it's worked great.

I think it took most of a day to get that to work, but I've probably had
close to 500 days of trouble free operation since then.

> I *might* be able to force it to share an IRQ with something else.  Would
> this be worth tampering with?

It is, as long as you're comfortable with the process and realize that
all this screwing around can, if you are unlucky, break something
physically. It's not likely to happen, but it is a small risk.

The thing you probably want to understand is that right now every
Ethernet packet that arrives has higher priority than your sound card or
your disk drives. IRQ11 beats IRQ14/15 for the disks or IRQ5 for the
sound card.

So, if your Ethernet adapter is a card, take it and the sound card out,
put the sound card in the Ethernet slot, and then reboot and see what
you get.

> > (Strange that the Promise is there in lspci but doesn't show up in
> > /proc/interrupts. Maybe some more knowledgeable Linux person could help
> > me understand why. I don't know...
> Since I wasn't ready to use it, I don't think I built drivers for it when I
> built the kernel.  Might this explain the discrepancy?

Possibly. Not sure. I don't remember building drivers for mine, but
that's another PC than this one.

I see that there have been many other response to this thread, so I'll
have to read what other said.


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