Playing DVD interfers with modem?

[Rick Stevens]

On Fri, 2008-02-01 at 16:34 -0500, Ric Moore wrote:
> On Fri, 2008-02-01 at 09:59 -0800, Rick Stevens wrote:
> > On Fri, 2008-02-01 at 00:19 -0500, Ric Moore wrote:
> > > When I play a video DVD the modem quits doing whatever it's doing.
> > > Strange. I'm running 32bit FC7 on a system with a 64bit AMD 3200 and 2
> > > gigs of memory. Both Xine and VLC exhibit the same behavior. I just
> > > tried gmplayer and it does the same thing, but the sound has static.
> > > That's weird, it never has before. Something else to fix. Sound on Xine
> > > or VLC is perfect. 
> > 
> > Uh, are the modem and the IDE port the DVD sharing an IRQ or something?
> > 
> > > So, how could playing a DVD foul up the modem? Is there some type of
> > > streaming to the network that could grab the serial line or the ppp
> > > session??
> > 
> > I can think of two things at least...the sharing of an IRQ or some other
> > hardware semaphore or simply the load put on the CPU by a soft modem.
> > However, with an AMD 3200, I don't think that's the issue.
> 
> Lordy Rick, I'm an old BBS sysop from back when. I have a RS Robotics
> external with all the bells and whistles in hardware, so I'm connected
> only by a serial cable. I'm gonna check out your suggestion about the
> IRQ though. I sure miss setting pin jumpers. Devices generally stayed
> where you put 'em, IRQ wise. Here's /proc/interrupts
> 
> # more interrupts
>            CPU0
>   0:        181   IO-APIC-edge      timer
>   1:      21093   IO-APIC-edge      i8042
>   7:          0   IO-APIC-edge      parport0
>   8:          1   IO-APIC-edge      rtc
>   9:          1   IO-APIC-fasteoi   acpi
>  12:          4   IO-APIC-edge      i8042
>  14:      45395   IO-APIC-edge      libata
>  15:          0   IO-APIC-edge      libata
>  16:        986   IO-APIC-fasteoi   ohci_hcd:usb1
>  17:     122468   IO-APIC-fasteoi   ohci_hcd:usb2
>  18:          0   IO-APIC-fasteoi   ohci_hcd:usb3
>  19:          3   IO-APIC-fasteoi   ehci_hcd:usb4
>  20:      71311   IO-APIC-fasteoi   libata
>  21:     566805   IO-APIC-fasteoi   ALi M5455, eth0
>  22:    1327729   IO-APIC-fasteoi   nvidia
> NMI:          0
> LOC:    2874529
> ERR:          0
> MIS:          0
> 
> I don't see IRQ 3 or 4 listed for serial port. Do I have to gink with
> uugetty or set serial? Is that the right place to look?? Ric

The IRQ won't show up unless something is on the serial port or using
it.  For example, my machine shows this normally:

  0:       1668   IO-APIC-edge      timer
  1:     163398   IO-APIC-edge      i8042
  6:          6   IO-APIC-edge      floppy

However, if I "agetty -L 9600 ttyS0", it shows this:

  0:       1668   IO-APIC-edge      timer
  1:     163146   IO-APIC-edge      i8042
  4:         25   IO-APIC-edge      serial
  6:          6   IO-APIC-edge      floppy

So, you need to look at it when the modem's active (or you've spawned
something like agetty on it).

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- Rick Stevens, Principal Engineer             rstevens at internap.com -
- CDN Systems, Internap, Inc.                http://www.internap.com -
-                                                                    -
-     Never put off 'til tommorrow what you can forget altogether!   -
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