Add callback for CPX app messages

[mfxjx000205]

Dear Bitcraze:

In the PR #1273, my collaborator @RavenLite commit a PR about fixing the CPX_F_APP in CPX protocol. Now this work will be carried forward by me.

In this PR, we fix three main problems:

1. We add a case about putting CPX_F_APP message into mixedQueue in cpx_internal_router.c to make sure that the CF can receive message with type CPX_F_APP.

2. We add a handle in main code cpx.c. As @krichardsson said last time:"You need to add a function pointer and a function where an app can register a handler function for the pointer."But we believe that, as the name of this message category(CPX_F_APP) suggests, processing this message should be done in a user-defined app. So we added only an alert for the received message.

3. We add a deepcopy function to carry the CPXpacket from cpxRx to user-defined cpx packet. We do this because we can't directly use the function named cpxInternalRouterReceiveOthers() in the app-layer due to the repeat reception. So we believe that a deep copy function is needed. Users can copy the packets received by the system to their own app without causing conflicts.

Thank you for your reviewing.

[krichardsson]

Thanks for your PR!

But we believe that, as the name of this message category(CPX_F_APP) suggests, processing this message should be done in a user-defined app. So we added only an alert for the received message.

I completely agree, and this is why I think the callback is what is needed.
I'm not sure I understand how your solution is supposed to work, how will the app be notified that data is available? This is what the callback would be used for.

I suggest something like this:

in cpx.h

typedef void (*cpxAppMessageHandlerCallback_t)(const CPXPacket_t* cpxRx);
void cpxRegisterAppMessageHandler(cpxAppMessageHandlerCallback_t callback);

and in cpx.c

void cpxRegisterAppMessageHandler(cpxAppMessageHandlerCallback_t callback) {
  appMessageHandlerCallback = callback;
}

// In the switch 

      case CPX_F_APP:
        if (appMessageHandlerCallback) {
          appMessageHandlerCallback(&cpxRx);
        }
        break;

This would enable an app to do something like:

void onCpxAppMessage(const CPXPacket_t* cpxRx) {
// Do stuff with the message, but quick to not block the router. Maybe a copy?
}

// Somewhere in the init code
cpxRegisterAppMessageHandler(onCpxAppMessage);

I don't think the deep copy function should be part of cpx.c, this is something an app can do if needed

What do you think?

[mfxjx000205]

Dear @krichardsson:

Thank you for your help!

We misunderstood you before, because in our project we didn't consider using callback functions. so we set a deep copy function in the firmware to be able to read CPX packages in the user defined app without conflicts.

According to your help, we took your suggestion to optimize the code, and now the PR submission is already the optimized version. In this version:

1. Callback function is set in cpx.c.

2. CPX_F_APP message is put into mixedQueue in cpx_internal_router.c

Thanks again for your excellent advice, callback functions are not used much in our projects , but this is very important.

[krichardsson]

Looking good, thanks for your contribution!
Merging