Add cast for compatibility with the next version of CurieBLE

[sandeepmistry]

Arduino and Intel are working on a new API for CurieBLE, progress can be seen here: arduino/ArduinoCore-arc32#337

There's a backwards compatibility layer with the existing BLEPeripheral based API, so for the most part no code changes will be needed for CurieBLE users once they upgrade.

However, we've overloaded BLECharacteristic::setEventHandler(...) with the following:

typedef void (*BLECharacteristicEventHandler)(BLEDevice bledev, BLECharacteristic characteristic);

typedef void (*BLECharacteristicEventHandlerOld)(BLECentral &central, BLECharacteristic &characteristic);

    void setEventHandler(BLECharacteristicEvent event, 
                         BLECharacteristicEventHandler eventHandler);
    void setEventHandler(BLECharacteristicEvent event, 
                         BLECharacteristicEventHandlerOld eventHandler);

So there's a tiny casting change needed in Firmata need for compatibility, only because a NULL value is passed into setEventHandler. For now we think adding a cast is the best solution to move forward, but are open to other ideas.

cc/ @facchinm @SidLeung @sgbihu @noelpaz @russmcinnis

[facchinm]

This patch is needed to pass the backwards-compatibility test for upcoming CurieBLE v2 library; however, since the APIs are not yet super stable, I'd recommend Intel team to run the test suite with this patch applied, while @soundanalogous should wait before merging it until the library is out (or at least the APIs are stable and merged in https://github.com/01org/corelibs-arduino101 mainline)

[soundanalogous]

I'm waiting to merge this until the CurieBLE v2 library is ready. Can someone on the Arduino or Intel side notify me when there is a CurieBLE RC is available.

[sandeepmistry]

@soundanalogous there's an RC of v2 available now, @facchinm has prepared some instructions on the Arduino forum: http://forum.arduino.cc/index.php?topic=443728.0

However, my initial testing did not go well (sketch compiles with this patch, but something is crashing), I've opened arduino/ArduinoCore-arc32#377 with Intel to track the problem. A member of the Arduino community has also opened arduino/ArduinoCore-arc32#387 to let Intel know about the compile error that this PR addresses.

Let me follow up with Intel in the next week or two, then we can let you know when things are stable for you to test.

[soundanalogous]

It's sounds like this has been resolved per the thread in the corelibs-arduino101 library. I'm travelling for the next week so I won't have time to test this on HW until I get back. If this needs to be merged earlier and someone can verify that the patch works and is backwards compatible the please verify. Otherwise I'll get to it sometime during the week of 2/20.

[sandeepmistry]

I've been testing an end to end scenario with Node.js (https://gist.github.com/soundanalogous/927360b797574ed50e27) and the latest CurieBLE master, things are still not functional for me.

After debugging for a bit found another CurieBLE issue: arduino/ArduinoCore-arc32#444

@soundanalogous I'll keep you updated on any further testing we do, however as I mentioned before, I don't expect any more changes will need to be made to the Arduino Firmata library.

[sandeepmistry]

@soundanalogous based on my testing in arduino/ArduinoCore-arc32#377 (comment), this should be good to merge now.

[soundanalogous]

This is still backwards compatible with older version of CurieBLE right?

[sandeepmistry]

Correct, I was actually testing the PR with v1.0.7 in arduino/ArduinoCore-arc32#377 (comment) also.

[soundanalogous]

Great! Thanks for all of your help with this!

[SidLeung]

@sandeepmistry , I should pull this PR in for the upcoming release, shouldn't I?

[SidLeung]

Oh! It's done. Pardon me.

[sandeepmistry]

@soundanalogous thanks for merging!

Do you know when the next version of the Firmata library is schedule to be released?

[soundanalogous]

I could cut a bugfix release this weekend.

[sandeepmistry]

A new bug fix release at your convenience would be great!

[soundanalogous]

v2.5.5 is out now: https://github.com/firmata/arduino/releases/tag/2.5.5

[sandeepmistry]

Thank you! I've updated the IDE side to use v2.5.5 in the hourly builds and in the next release (arduino/Arduino@197fe6d).