Small update: I followed the track Sven started in November a bit through kernel sources and found that the BUG-ON() statement which causes the crash might be itself a bug, because it blocks a code path that seems legit to me. At least, when I experimentally removed the BUG_ON(), aplay does not crash any more but produces a i2s WS signal for the right duration :-)
However, no sound yet - I haven't been able yet to check if this is a problem of my hardware (with very difficult to solder MAX98357A) or still DMA not piping the data to the i2s. I'm also trying to check with the author of that BUG_ON statement to find out why exactly he did put it there.
It seems like Onion only partly discontinued the Rocki expansion. I've gone through Onion's blog. Shipping of the Rocki expansion is still mentioned in the Kickstarter and Indiegogo updates on February 22 and 24 (https://onion.io/blog-kickstarter-update-february-22-2017/). About two weeks later, in the Kickstarter update on March 6, it is listed as no longer available due to manufacturing difficulties. Nothing is said in that particular update about the Rocki expansions that were actually shipped. But in the Kickstarter and Indiegogo updates on march 8, they repeat that it is no longer available. But they also add, "This applies to backers who have not yet completed the survey. If you have already completed your survey and ordered these items, you will be getting them!". And that's the last mentioning of the Rocki expansion in Onion's blog. So, of course I am hoping for some kind of documentation.
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