[LAU] Hardware latency of firewire controller

My colleague bought a Presonus FP10 firewire audio interface, which
reports working nice in Linux. Moreover he owns a firewire controller
made by Sunix with a Texas Instruments chipset. He tells us that for
having jackd working without xrun and no other artifacts he needs to
use 512 frame/periods, then latency is 34ms, which could be considered
awful as this card is able to work with 2ms latency using other
operating systems.

He checked IRQ and saw that the firewire controller shared IRQ with
the network interface. Check out output of lspci -v .

03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 01)
Subsystem: Giga-byte Technology Unknown device e000
Flags: bus master, fast devsel, latency 0, IRQ 17
I/O ports at a000 [size=256]
Memory at eb000000 (64-bit, non-prefetchable) [size=4K]
[virtual] Expansion ROM at 50000000 [disabled] [size=64K]
Capabilities: <access denied>

04:01.0 FireWire (IEEE 1394): Texas Instruments TSB43AB23
IEEE-1394a-2000 Controller (PHY/Link) (prog-if 10 [OHCI])
Flags: bus master, medium devsel, latency 32, IRQ 17
Memory at ec004000 (32-bit, non-prefetchable) [size=2K]
Memory at ec000000 (32-bit, non-prefetchable) [size=16K]
Capabilities: <access denied>

lspci lists 18 devices and every one of then reports 0 latency except
the firewire controller. And hardware latency is 32ms, very near the
34ms of audio latency reported by jackd. So one could think that if
the firewire controller added no latency, audio latency could be as
low as 2ms. Strange, isn't it?

So it looks that audio latency achievable by jackd is limited by
hardware latency achievable by the firewire controller.

He even tried locating a PCI slot that doesn't share IRQ and running
the kernel with the noapic and nolapic options so the system ends
reporting the sound card in the IRQ 11, which is nice. No change,
hardware latency is 32ms in any case.

marcel@email-addr-hidden:~$ uname -a
Linux ubuntu 2.6.22-14-rt #1 SMP PREEMPT RT Tue Feb 12 09:57:10 UTC
2008 i686 GNU/Linux

Anything else can be tested? Or should he put back the PCI firewire
controller and buy another? Which one? Any ideas welcome. Personal
answers not to the list also welcome.

Cordially, Ismael

--
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