Interfacing native code to hardware functions

[Schell, Jon]

I am trying to create a simple app for testing that will toggle an LED
on the phone as needed. I have the NDK set up and my c code compiles,
but I don't know how to link it to the actual hardware function that
would set the LED. I'm using the actual source code for the hardware,
it's not in an exposed library. Do I need to create a static library
for it to use? Would it maybe be easier to add an android API for this
somehow rather than using the NDK?

For reference, this is Android 2.1 on a Qualcomm MSM7627.

Jonathan

[David Turner]

Applications typically don't have permissions to access the hardware devices under /dev/<something>.

Usually, this access is reserved for a system daemon / service, which provides an API usable by normal applications and controls what they can do with it.

You should try asking android-porting for more, android-ndk is strictly for developing applications.

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[Glenn Kasten]

Since this LED hardware capability is apparently not exposed by the
standard Android platform APIs in SDK or NDK, you may want to post
your question to one of the platform groups; see http://source.android.com/community/
Of those listed, android-porting looks like it might be closest.

[mic _]

Depends on which LED you're talking about. One or more of them might be controllable through /sys/class/leds/ (e.g. echo 255 > /sys/class/leds/red/brightness). But it's not really NDK-related, so you'll have to find more details elsewhere.

/Michael

[jon.schell]

Ok, I tested this with adb and it is the correct led. So, how would I
set this from my application?

Jonathan

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[Chris Stratton]

Barring permissions issues, do what echo does - just open the special
file, write to it, and close it again.

But the adb shell has some permissions to things that applications do
not, so this might not work programmatically on an unrooted device.
Try the same test in connectbot's local terminal shell (which has
ordinary application privileges) for comparison.

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