Re: DRAWS total failure Re: DRAWS audio crosstalk? #draws #direwolf

Annaliese McDermond

On Dec 13, 2018, at 3:06 PM, Brian Badger <brian@...> wrote:


I appreciate your time on this. I have been using Raspbian for 5 years, with projects all through the house, but this is the first time I've seen an overlay work like this. I have set dtparam=audio=on on other projects and it didn't come at the end. When I was told to put dtparam=audio=on at the end, I was expecting the dtoverlay= to come after dtoverlay=draws since I assumed I had to close scope on the "draws" overlay in order to send a param to the main scope of the device tree.

Instead it was exactly backwards of that in every respect. My pi experience is working against me.
In the HAT spec, there’s room to put a chunk of device tree on a flash chip on the hardware itself. If the firmware sees this, it will load up that device tree overlay and merge it with the rest of the stuff it happens to be doing. With the UDRC we did this, although with changes to the kernel the HAT-embedded device tree became invalid. I’m working on a field programmer for that, but I only have a certain number of amateur time units with which to work on this kinda thing.

What dtoverlay= does is clears out all device tree overlays whether they come from the HAT flash rom, or previous parameters in config.txt. We probably don’t really need it for the draws, but it’s absolutely necessary for udrc. Any dtoverlay/dtparam statements that come before this will essentially be ignored because dtoverlay= clears all of them out. So, you need to do the dtoverlay= first before you start loading other overlays or parameters. We would love to put the DRAWS overlay on the flash prom, but it slipped by us in testing that we’ve used a flash chip that’s too small to fit the overlay, hence you just have to use config.txt to load the overlay instead.

Hopefully that answers some of your questions about how the firmware loads all the DT stuff.


Brian N0KZ

Annaliese McDermond (NH6Z)
Xenotropic Systems

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