[asterisk-users] 8-span TE820 card and interrupts

Tony Mountifield tony at softins.co.uk
Wed Mar 21 11:17:51 CDT 2012

In article <20120321151844.GA11473 at digium.com>,
Shaun Ruffell <sruffell at digium.com> wrote:
> On Wed, Mar 21, 2012 at 12:45:37PM +0000, Tony Mountifield wrote:
> >
> > Over the years I have experienced a few interrupt issues when using some
> > of the Digium E1/T1 cards with Zaptel drivers, and usually resolved them
> > by disabling USB devices in the motherboard BIOS settings.
> > 
> > Now more and more systems are coming without PS/2 connections, so USB is
> > needed for the keyboard or KVM.
> > 
> > I never knew whether these conflict issues were down to the design of the
> > card, the motherboard, the Zaptel drivers or the kernel.
> My personal experience is these issues were a result of the BIOS
> using the system management interrupt to emulate a legacy keyboard.
> I.e., so you could plug in a USB keyboard and boot DOS on the system
> and have DOS think it was a PS/2 keyboard.

I think you misunderstood what I was asking - my fault for running two
things together. The interrupt issues I experienced in the past were
on systems that had a proper PS/2 keyboard on IRQ 12, and were nothing
to do with the keyboard. They were due to the USB subsystem, even though
I had no USB devices connected. Turning off all USB controllers in the
BIOS would fix the interrupt issues, due to the E1 card then having an
IRQ all to itself.

I was just concerned that if interrupts were still an issue due to IRQ
conflicts between the E1 card and the USB drivers, this solution
would no longer be available to me if a system required a USB keyboard
due to the lack of a PS/2 port.

> > I need soon to build an 8-span E1 system using the Digium TE820 PCIe card,
> > and want to know whether I am likely to have to solve similar issues, or
> > if they are now history with newer kernels and DAHDI instead of Zaptel.
> The TE820, like the 5th generation dual/quad span digital cards,
> have an ability to grow latency in the audio path to acommodate
> systems that can't guarantee < 1ms interrupt service times. So I
> would be surprised if you still have issues.

OK, thanks.

> > I would be interested in any comments from anyone with experience in this
> > area. Also, can anyone easily tell me in which version of DAHDI support
> > for the TE820 was introduced? (If not, I'm happy to go and search SVN)
> 2.6.0 was the first release that supports the TE820. (or
> 2.6.1) will be tagged here very shortly.
> > Finally, does anyone have a feel for how much CPU power would be required
> > to run Meetme with DAHDI mixing if all 240 channels were active in various
> > conferences? (Yes, I know about ConfBridge, but my application currently
> > needs to use MeetMe).
> 240 channels in meetme comming from an 8-span digital card? I would
> have to measure it...but my guess is a pretty beefy system. In this
> configuration, more speed on less cores would serve you better than
> more cores.

Yes, I wondered about that, having studied how the Zaptel mixing works.
Presumably, ConfBridge does thread-local mixing in user space and would
be able to make full use of multiple cores?

Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org

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