RE: Port an MBED design to non-MBED - Phase 5: OO Callbacks Simplified

Jan Cumps — Tue, 03 Nov 2020 20:19:08 GMT

I was going to write a follow up blog. But I can conclude this in the comments too. It's a 3 star post anyways so not going to burn more energy.

There are 2 use cases.

The calling object knows it's going to be called by an interrupt or timer, and will deal with the context.

In that case, we use a low level api. We pass the object pointer and a static function reference:

The "class to be called has to have a special static member that's "in the know"

[embed:dc8ab71f-3b98-42d9-b0f6-e21e02a0f8e2:3ef06e6b-9b7d-4651-b12d-db8be7f5e991:type=c_cpp&text=protected%3A%0A++static+void+_timeouthandler%28uint32_t+id%29%3B%0A++Callback%3Cvoid%28%29%3E+_function%3B]

The implementation of the handler has to know how to translate that again into an object instance, and call the member:

[embed:dc8ab71f-3b98-42d9-b0f6-e21e02a0f8e2:3ef06e6b-9b7d-4651-b12d-db8be7f5e991:type=c_cpp&text=void+Timeout%3A%3A_timeouthandler%28uint32_t+id%29+%7B%0A++Timeout+*handler+%3D+%28Timeout*%29id%3B%0A++Callback%3Cvoid%28%29%3E+local+%3D+handler-%3E_function%3B%0A++handler-%3Edetach%28%29%3B%0A++local.call%28%29%3B%0A%7D]

When using the full object oriented way, where the compiler can do some work for us:

[embed:dc8ab71f-3b98-42d9-b0f6-e21e02a0f8e2:3ef06e6b-9b7d-4651-b12d-db8be7f5e991:type=c_cpp&text=++%2F%2F+Initialize+Radio+driver%0A++RadioEvents.TxDone+%3D+OnTxDone%3B%0A%2F%2F+...%0A++++dio0.rise%28+callback%28+this%2C+static_cast%3C+TriggerMB1xAS+%3E+%28+irqHandlers%5B0%5D+%29+%29+%29%3B]

The object and method that are called don't have to know that there's a timer or interrupt involved. A normal class member will do.

The difference is there for those that appreciate it. No explicit rendering an object to a void pointer. Strong typing all the way (with the developer protection by compiler instead of debugger that comes with that) without runtime overhead.

RE: Port an MBED design to non-MBED - Phase 5: OO Callbacks Simplified

DAB — Tue, 03 Nov 2020 18:50:12 GMT

Nice update Jan.

DAB