[alsa-devel] Enhance support for SigmaDSP chips

[Daniel Mack]

Hi Lars,

(taking off Cliff's email address, as it's apparently not valid any more).


On 11.04.2013 12:51, Lars-Peter Clausen wrote:
> On 04/11/2013 11:56 AM, Daniel Mack wrote:
>> Hi Lars,
>> Hi Cliff,
>>
>> I'm looking into the SigmaDSP AD1701 support, as a new prospective
>> project will use it. What's going to be used on this chip is not the
>> DAC/ADC features though, but the internal, programmable DSP things, and
>> designers will use the SigmaStudio IDE to generate the firmware.
>>
>> So I'm wondering how to support this kind of chip properly in ALSA,
>> which is not straight-forward, as the controls exported by it are
>> specific to the loaded firmware of course. Also, the IDE is free to
>> re-allocate every sub-addresses of its controls when something changes
>> in the layout of the building blocks.
>>
>> One idea I have in mind is to have a little parser script that reads the
>> generated sources of the IDE and dump a device-tree node snippet which
>> can then be put into the final DT. The driver would need to learn about
>> how to interpret that DT nodes, which will most likely just contain a
>> name, a sub-address, along with some mask and shift values.
>>
>> I wanted to ask for your opinion on that before I start. Have you ever
>> used any of the DSP features from ALSA/ASoC? Are there any pitfalls I
>> should be aware of? Is anyone actively working on improvements on the
>> driver?
>>
>> An alternative approach is to write a userspace library of course, but
>> that's going to be problematic once anybody wants to use the DSP
>> features in parallel to the DAC/ADC.
> 
> Hi,
> 
> I just yesterday wrote a small post how you can program the DSP registers.
> http://ez.analog.com/message/83094#83094

Good timing :) Yes, I would add something like this, but in a generic
manner of course.

> I'd like to be able to put the information about the different algorithms
> into the DSP firmware file itself, so we can auto instantiate the controls
> from the driver. The problem is that it is not so easy to generalize the
> export of the algorithms from SigmaStudio.

But just to understand this right: the firmware exported by SigmaStudio
is already what the driver loads via the kernel firmware interface, right?

> Another problem is that you don't know how to calculate the algorithm
> parameters at runtime for some of the more complex algorithms.

I would just want to set the controls as specified by the exported
header file, whatever kind of control that is. I haven't done real-world
tests yet, but the output of a example project doesn't seem very
complicated. Which 'more complex algorithms' are you referring to?

> I don't think it's a good idea to put the control info into the devicetree
> and would rather prefer to see them go into the firmware.

I thought about this too, but after all, the DT describes the hardware,
and the hardware in this case is something that can be programmed. The
idea would be to have that script that generates the DT fragment, and
leave it up to the user to decide which controls to make accessible by
the driver.

>From the driver's perspective, I don't know if defining a binary
interface format inside the firmware blob and parsing it at run-time is
really easier to achieve than using the DT, especially as we have all
convenient functions to read properties and iterate over nodes already
prepared. But as I don't have the full picture of the DSPs yet, I might
overlook the subtle details.

> But as I said
> auto-generating this from exported SigmaStudio files is not so easy. So
> maybe manually creating the control info table might be an option.
> 
> Btw. in case you haven't seen it the SigmaTcp tools is quite useful during
> the development of the firmware since it allows you to connect SigmaStudio
> directly to the DSP on the board.
> http://wiki.analog.com/resources/tools-software/linux-software/sigmatcp

Yes, I've seen this. That's a very nice option for the development
process. Thanks for mentioning it!


Daniel