Re: polling for bluetooth events
Re: polling for bluetooth events
- Subject: Re: polling for bluetooth events
- From: Joseph Kelly <email@hidden>
- Date: Mon, 10 Mar 2008 10:34:45 -0700
So basically you require a polling model -- occasionally you'll poll
for any available input, process it, and then return to whatever it
is you're doing. Unfortunately, the bluetooth api is dependent on the
main thread run-loop (unlike HID which has a queueing mode), i.e.
your main thread should spend its life handling events and otherwise
remaining idle, and you would offload cpu intensive tasks to worker
threads.
Have you considered handing off your bluetooth stuff to a separate
process?
So basically, the process that needs to poll for events will spawn
the bluetooth process (which creates a broadcast CFMessagePort), set
up an event fifo, create a listener thread which creates a
CFMessagePort to the bluetooth process. Then the bluetooth process
connects to the device, sets up callbacks for data, then sits in the
run loop. When data comes in from the wiimote to your bluetooth
process' callbacks, it forwards the data over the message port to the
listener thread, the listener thread stuffs the event into the event
fifo. And then whenever your main process polls for events, it simply
gets the lock on the event fifo, checks for available data, and unlocks.
It's not the cleanest solution, but I think it should get you a
continuous flow of data from the device.
Joe K.
On Mar 7, 2008, at 6:08 PM, Hans-Christoph Steiner wrote:
Pd (aka Pure Data) has two processes that communicate via a network
socket. There is a Tcl/Tk process that handles the GUI ('pd-gui')
and the C process ('pd') that handles all of the digital signal
processing. It is a realtime system, so it has its own cooperative
scheduler. All processing needs to happen within the timeslice, or
it will cause an interruption in the processing. So, for example,
when I connect to the device, it causes everything to hang until
the device is connected, and CFRunLoopStop() is called.
Since Tcl/Tk is based on Carbon, AFAIK, there is probably a
CFRunLoop in it. But that's a separate process, so the 'pd'
process isn't using any of that.
I wrote HID support for Pd, and I just polled the event queue, it
works well. I was hoping for something like that for Bluetooth HID
events. In particular, I am working on getting data from a
Nintendo WiiRemote.
.hc
On Mar 7, 2008, at 8:34 PM, Joseph Kelly wrote:
Much of the user space Bluetooth API depends on run loops, i.e.
for getting data to and from the kernel. It's surprising that your
GUI framework itself does not rely on run loops. How does it
respond to user input etc. ?
Unfortunately, I found that some Bluetooth calls only run reliably
on the main thread, at least on Tiger and earlier.
Maybe you could explain your architecture a bit more. The model
I've been using is I set up a callback for when data comes from
the device, then I just return and wait; when the user does
something which causes me to send commands to the device, and when
I return from doing that (i.e. program flow returns to the event
manager and the runloop code) I then get my data-in callbacks
which I respond to.
Joe K.
On Mar 7, 2008, at 12:55 PM, Hans-Christoph Steiner wrote:
I am currently in the process of adding bluetooth HID support to
Pure Data, a realtime, visual programming language for sound,
video, etc. The GUI is all written in Tcl/Tk, so we are not
handling a CFRunLoop at all.
I have gotten device searching and connection working by using
CFRunLoopRun() then sticking CFRunLoopStop(CFRunLoopGetCurrent())
the end of the of the inquiry completion callback. I am trying
to get the same thing working for getting events, but I haven't
been able to.
Ideally, I would be able to poll for bluetooth events, is there a
way to do that, outside of creating a separate thread to handle
the event callbacks? Maybe something with CFRunLoopRunInMode()?
Here's the code in question:
http://pure-data.svn.sourceforge.net/viewvc/pure-data/trunk/
externals/io/wiiremote/
.hc
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