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

[Guillaume Pellerin]

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