[maemo-developers] [maemo-developers] DSP programming

[From: Simon Pickering]

Hi All,

I've had some time and have picked up where I left off, but this time using my
N800. The result is good news :) (but a rather long and meandering email). The
DSP seems very well behaved (no resets leading to reboots) and the couple of
demos I've tried worked fine. I was quite surprised after the hassles I had with
the 770. I don't know whether I've done something different or whether the setup
on the N800 (hardware/software) has helped.

Anyway, instructions largely as before, Ti toolchain all the same, etc.

I tested the demo_console and test7 demos, both worked fine.

I made my own Makefiles pointing to the locations of my toolchain. These are
available in the tarballs of the DSP code directories I've placed at
http://people.bath.ac.uk/enpsgp/nokia770/dsp/. They are copies of the ones from
the DSP_Gateway33_spec.pdf document. The code was also copied from here, but
it's available in the dspgw-3.3-dsp.tar.gz tarball from the DSP Gateway page.
You'll also need the ARM-side code which is in dspgw-3.3-arm.tar.gz.

A couple of notes at this point (about copying from the pdfs from the DSP
Gateway site): Any \ characters appears as a ¥ in the pdfs and the " sometimes
comes out as a different character (smart quote) so make sure you check your
code if you start getting weird errors (the last one had me scratching my head
for a while as they look pretty much the same in my editor).

You'll also need to remove references to the <asm/arch/omapdsp.h> include file.
I don't have this, the tarball demos don't have this line either (and are
otherwise identical to the pdfs). No idea what it's for.

After compiling your code, you'll need to place the DSP-side object file (*.o)
in /lib/dsp/modules/, you'll also need to make an entry in the
/lib/dsp/dsp_dld_avs.conf file.

My addition lines looks like this:

demo_console    _task_demo_console      1       /lib/dsp/modules/demo_console.o
test7           _task_test7             1       /lib/dsp/modules/test7.o

I didn't add the name of any cmd files to the last column in the conf file
(though this is shown in the pdf instructions), mainly because it said it's
optional, and because I didn't have one (or the source for one, etc.). I need to
clarify just how these are optional, and what they achieve when they are listed
in the conf file. Possibly overrides to the settings in the module itself?

You'll then want to run "dsp_dld" to reload the module list, but this will
complain that it can't find the conf file:

Nokia-N800-10:~# dsp_dld
sending SIGBUS signal to all task users...
killing pid 832.
killing pid 827.
killing pid 1582.
Can't open /lib/dsp/dsp_dld.conf

So you need to create a symlink from the actual file dsp_dld_avs.conf, to the
one it expects dsp_dld.conf (both in the /lib/dsp/ directory). Then try again
and you'll see something like this:

Nokia-N800-10:~# dsp_dld
sending SIGBUS signal to all task users...
killing pid 4234.
killing pid 4236.
killing pid 4235.
mapping external memory: adr = 0x028000, size = 0x1000
mapping external memory: adr = 0x100000, size = 0x200000
mapping external memory: adr = 0x400000, size = 0x180000
detected binary version 3.3.0.0
setting DSP reset vector to 0x10389e
releasing DSP reset
DSP configuration ...
  succeeded.

Then run the ARM-side binaries and see results. E.g.:

Nokia-N800-10:~# ./test7
32 bytes written
32 bytes read
Aaaaabbbbbcccccdddddeeeeefffffgg

If you see a message like this:

Nokia-N800-10:~# ./demo_console
open: No such file or directory

It means you've either not added the module to the /lib/dsp/dsp_dld_avs.conf
file, or you've not run dsp_dld to refresh the DSP.

I also built the demo_fb demo, but couldn't get it to do anything as I couldn't
share the framebuffer. Using "dspctl fbexport" produces an error (better than
the resets of old), and there's no /proc/dsp/ or /sys/devices/platform/dsp/mmu
or mem entries to look at anymore to see whether my choice of address is wrong.
Obviously something's changed. There are also no longer any dsp tasks that
access the framebuffer. Perhaps this functionality has been disabled?

Anyway, the fact the demos work means that people can now happily experiment
with the DSP. It would be nice if Nokia could release a header file for any
sound related functions contained in the avs_kernel, so that we can link into
those rather than having to fiddle about and re-write a codec for the audio
hardware (though there is a demo on the Ti website that might be a good start -
DSP OGG sink on the DSP anyone?). Is this possible (releasing the header file) -
it may not be if this code belongs to a subcontractor, could we know one way or
the other?

I'm going to look at using the DSP with Octave (via oct files) for doing fast
ffts, etc. I'd also like to see whether it might help with speeding up JPEG
decoding, which leads me rather obliquely onto the IVA. 

I've tried searching for this, but all I seem to get are promo. pdfs about how
it's included in various OMAPs, and how wonderful it is, but nothing about what
it actually is. For example, is it like the DSP, where it runs its own kernel,
or is it a chip with set functionality that would have a limited set of function
calls, etc.? Is there some technical documentation available for it anywhere? I
suppose this question may be better asked on the linux-omap-open-source mailing
list as some people there have been/are working on a DSP-IVA task bridge (e.g.
see http://komalshah.blogspot.com/), but I thought I'd tack it on here and see
whether anyone has run across anything.

Cheers,


Simon