[LAD] Optimized device driver to Fast Track Pro (start developing)

[Rodrigo T O Ladeira]

Hi !!!

   I am using a jack_delay to measure the Fast Track Pro latency, but
something strange happens...It doesn't matter what configuration I am doing
on Jack that the latency value always is increase during the time... like
the result below:

ladeira at debian:~/Downloads/jack_delay$ ./jack_delay -E -O system:playback_1
-I system:capture_1
???     412.673 frames    8.597 ms
???     412.671 frames    8.597 ms
???     412.671 frames    8.597 ms
???     413.487 frames    8.614 ms
???     413.657 frames    8.618 ms
???     413.670 frames    8.618 ms
???     413.671 frames    8.618 ms
???     413.671 frames    8.618 ms
???     413.671 frames    8.618 ms
???     414.455 frames    8.634 ms
???     414.654 frames    8.639 ms
???     414.670 frames    8.639 ms

What am I doing wrong??

2012/11/26 Guillaume Pellerin <lists at parisson.com>

> On 23/11/2012 20:01, rodrigo at angoera.com.br wrote:
> >
> > Hi !!!!!
> >
> >   The Fast Track Pro is USB 1.0, the max bandwidth is 12Mb/s. The
> TUSB3200 has
> > the isochronous USB transfer mode, that can occupy about 90% of the USB
> > bandwidth... Using 4 channel (2 IN and 2 OUT) with right and left, and
> 24 bits
> > (3 bytes each, in total 4(channel) * 2(left,right) * 3(data) = 24 bytes
> ) The
> > max bandwidth  that could communicate is about 12Mbits/s = 1.5 Mbytes/s
> | 1.5
> > Mbytes/s * 0.9 = 1.2 MBytes/s --> 1.2MBytes/s / 24 bytes = 50Khz ... So
> the
> > maximum USB 1.0 with 24 bits is 4 chanel in 48KHz...
> >
>
> You're absolutely right, the 24 bits 4 channels mode would be only
> accessible in
> 48 kHz samplerate.
>
> >   I would like to know how it works the interface between USB AUDIO
> CLASS device
> > driver and the USB-AUDIO Alsa Device driver. And how does the isochronous
> > comunication works inside the kernel? Because I am using an RT Kernel
> and I
> > would like to set with the high priority this communication.
> >
>
> I don't really know how does the isochronous, but applying usual RT
> security
> audio rules seems sufficient to get high priority access and then very low
> latency (got 3 ms here with few audio realtime processes..).
>
> Further info here:
>
> http://joegiampaoli.blogspot.fr/2011/06/m-audio-fast-track-pro-for-debian-linux.html
>
> G
>
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