[PD] HID APIs and PlayStation Move LED support

[Mikael Bouillot]

Hello list,

I need to get access to a PlayStation Move Motion Controller [1] from Pure Data.
All inputs (buttons & sensors) and outputs (LEDs & rumble) should be accessible.
Basically, I need the equivalent of the [pd-wiimote] object, but for the psmove.

I have spent the last few days exploring the various libraries, drivers and APIs
that relate to my problem, but now I need some help to make sense of it all.

First, I'm on Linux. So I connected the controller by bluetooth, and after
loading the hid-sony kernel module, I got my input devices (/dev/input/jsX and
/dev/input/eventX). I found out that LED support for the Move controller was
added in kernel 4.2, so I upgraded my kernel.

I then tried accessing it with [hid], and it worked fine but only for inputs.
The doc says "For those interested in output support, checkout the alpha
[hidio]", so I tried that next, but I couldn't seem to find the LED controls on
my device.

That's when I realized what's wrong:

First, both [hid] and [hidio] use the Linux input API as backend ("evdev"),
rather than the lower-level "hiddev" or "hidraw" APIs. Basically, that means
that *all* communication from PD to the device *must* pass through the hid-sony
driver.

Second, the hid-sony driver doesn't seem to expose the LEDs through the evdev
API. Instead, what it does is register the LEDs through the Linux LED subsystem
(with led_classdev_register(), accessible through /sys/class/leds/*). That's why
I wasn't seeing any LEDs on my device with [hidio].

Third, even if the hid-sony driver *did* expose the LEDs through the evdev API,
this API only supports binary (on/off) LEDs, not variable brightness ones like
on the Move controller.

The net effect of this is that it's effectively impossible to control my LEDs using
[hidio]. I did write a quick hack to control the LEDs through /dev/class/leds and
it worked fine, but that's not a realistic option: I would like the whole device
to be controlled through a single object.


So here I am, wondering what to do next:

a) I could use the existing [hidio] to get inputs and control force-feedback,
   but I would then need a second object to control the LEDs,
b) I could write a dedicated object ("pd-psmove") that would bind to a low-level
   API (hidraw) and get me all that I need but would much less general,
c) or I could write a general input interface ("pd-hidraw") that would provide
   lower-level access to the HID stack than [hid] or [hidraw].

I have read the hidio paper [2], but that doesn't seem to address my main
problem of being restricted by the limitations of the chosen backend. I would
very much appreciate any suggestion, especially from the hidio authors.


Thanks in advance,

Mikael

[1] https://en.wikipedia.org/wiki/PlayStation_Move#Motion_controller
[2] A Unified Toolkit for Accessing Human Interface Devices in Pure Data and Max/MSP
    (http://alumni.media.mit.edu/~dmerrill/publications/dmerrill_NIME07-HID.pdf)