I did a quick test this morning on the BeagleBone and XMOS, with
squeezelite , without top running I get clicks every 5-10 secs or so,
and when top is running I always get a click when top refreshes. With
sox playing a wav file I get a click every 2-3 minutes and occasionally
a click from top. 

The UAC1 async seems to be solid no matter what. 

I have been looking at the freescale processors, I don't think the imx5
line will do us good, they are just missing too many things. The imx6
looks like it might do well for us. It has built in HDMI, S/PDIF, I2S,
ehci USB, good memory interface. There are two devel boards, both for
$399, the SABRE board looks closer to what we want, there  is a good
probability that the image that runs on it will run directly on what I
want to build. Unfortunately it comes with android on the SD card so  we
will have to get a linux image (they say they have them). These are
actually quite inexpensive, less than half the price of the TI ones. 

There are three reasons that keep me from being enthusiastic about
these:
1; they do  not have device library files for the tools I use, I will
have to make them myself
2; the ball  layout is not optimized to make it  easy  to route. This
takes an 8 layer board and more work. Fortunately we don't really use a
lot of signals
3; only single memory port, this makes routing 2 chips (to get 512MB)
much  harder

One interesting aspect of the SABRE board is that they give you the
board layout files and  encourage you to use them in your design.
Unfortunately they are the wrong format, but I can look at them and see
how they did it. This will probably help mitigate 2 and 3. 


The AM3874 is a wonderful chip from every aspect except non ehci. Even
though it has more pins, they layout has been optimized to make it much
easier to route, AND they have the library files in the format I use. It
has two memory controlers which makes memory layout much easier AND 
gives you twice the  memory bandwidth. The USB controller does have
hardware scheduling but it is not ehci, without testing we don't know
whether it will work well.

I did look at the Allwinner A10, unfortunately detailed documentation is
non existant, the only thing  I can find is the 83 page "spec sheet"
which doesn't really say much. I get the impression you only get the
real data when you sign an NDA with the company, which is a little 
difficult for a comunity  project. It may be a great chip, but I just
get a very bad vibe from it, that things are going to be almost there
but not fully implemented properly. But you can get a cubieboard for $50
to try it out. Getting small quantities  for a project such as ours is
also going to be tough, I have not found it at any distributors and
companies such as this  usually only sell  in 1K lots.  One interesting
aspect is that the imx6 is almost the same price for a way more capable
chip. 

I think I'm trying to convince myself that the imx6 is the way to go. If
so its $399 to get the demo board, which is a little out of my pocket
range right now. If we decide on this I will need some help from the
"community funding" part. 

John S.


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