I just made a short demo for the updated version of the Rhythmic Delay program I wrote to run on the Daisy via the Terrarium PCB (from PedalPCB). The program is inspired by the Binson Echorec and there is more information on this updated version (and the original) here. The major components of the update are getting rid of the 1kHz whine (by minimizing the blocksize) and adding Age & Swell controls.
The program code is available here. There is also a simplified version of the program here which has a lot of comments and could be a good starting place for someone trying to make their own delay. The code is written for the Terrarium, but I think porting it to the Petal (or some other hardware) should be straightforward.