Freitag, 1. Juni 2012

Bluetooth on Linux: Fixing hidapi's HID enumeration

One obvious goal of the PS Move API is to be cross-platform. On Linux right now, we can get the controller working via USB with no problems, but Bluetooth devices are not found via hidapi's hid_enumerate() method. One could work around this by opening the /dev/hidraw[0-9]* devices directly, and picking one. However this is kludgy and would require another special-case. The reason why the hid_enumerate() method does not work on Linux is because it always tries to find the USB device for a given hidraw device (even if the hidraw device is a Bluetooth one) and returns the VID/PID from there (this works fine for USB devices, but in case of Bluetooth devices what is returned is the VID/PID of the Bluetooth host adapter, which is not what we are interested in).

As a workaround, I've now implemented a better detection mechanism based on the sysfs path of the hidraw file. For Bluetooth devices, the path could look like this:


For USB devices, it could look like this:


In the case of the PS Move Motion Controller, the vendor ID is 0x054c and the product ID is 0x03d5. I've highlighted the occurence of these IDs in boldface above. Given that the hidapi already determines the sysfs path of the hidraw device, it's easy to write a function that extracts the IDs from the path. I've done so now in a patch against hidapi: commit 8ba92edb519 in thp/hidapi.

In order to get it merged into hidapi upstream, I've created pull request #62 at the signal11/hidapi repository on Github. Let's see if I have to rework/improve the patch or if it will be accepted.

After the patch has been merged (you can merge it locally or clone from my hidapi repo), connecting to the PS Move on Linux will become even easier. The only part remaining then is figuring out the permission problems on the hidraw devices (we could probably fix this with some udev rules) and getting Bluez' bluetoothd to reliably accept connections from new PS Move controllers.

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