Re: [Xylo-SDR] Saxo

[Philip Covington <p.covington@gmail.com>]

Hi Helmut,

Comments below:

On 1/23/06, vk4str <vk4str@netspace.net.au> wrote:

> Bulk transport is unuseable for real audio. Bulk guarantees 100% correct
> data content transfer but does not guarantee delivery on time!

I am not so sure that it is unusable for audio with USB 2.0.  I would
agree in the USB 1.1 case.

> Whereas isochronous transfer does not guarantee 100% correct data
> content but delivery will always be on time. Meaning that you could get
> an incorrect bit delivered now and then but always on time. That is a
> must for audio.

I think iso mode was a kludge added to make USB 1 work with streaming
audio type applications.  Most of the USB 2.0 devices that I have seen
do not use iso mode since block mode is faster.

> Phil, I suggest you abandon bulk transfer for audio because you will be
> wasting your time. The other thing is that you will not achieve low
> latency transport when you are not using the OS kernel drivers which
> have been worked over pretty well by M$. usbaudio.sys has only one small
> bug left the experts claim.

I don't think that block transfer is a problem.  The USRP can get 32
MBPS throughput with block transfer/USB 2.0.  I think the problem that
Phil H is having relates to how the Xylo is set up as far as
endpoints, the FIFO size/mode used, and the firmware.

73 de Phil C