OK, so absent any information whatsoever I made my own daemon.
Starting from old and non-functioning servoblaster code I
- removed all the dma/pwm related stuff
- changed the name(s) to protect the guilty and point at the innocent
- completely rewrote the input parsing so it actually worked for '+X%' instead of making a total pigs-ear
- changed to maintain a list of the current % of motion range rather than the simply annoying 'tick' counts
- added access to the PCA9685 via pigpiod
- ran it about eleventy-brazillion times trying to debug odd cases
T'ain't perfect, not by a long way but it does seem to function decently so far. It doesn't suck up cycles.It makes servos go where you tell'em to go. It could do withanother option to set the i2c address since the PCA9685 can be set to talk on a fairly wide variety. It would be nice to be able to make the servos move smoothly from one position to another with a nice acceleration curve.
Code & makefile & init-script here -