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CC2541 HCI over serial interface programming model

Stefan Hofmann53
Prodigy 20 points

Other Parts Discussed in Thread: CC2541, CC2640

Hi,

I am developing an embedded application which needs to communicate with some other hardware over BLE. The Bluetooth adapter used on both sides is a CC2541. Communication with the CC2541 takes place over a serial interface. The operating system is Linux. Even if this seems simple at the first glance, there a some points, which are still not clear to me. So I hope I can clearify them now. For communication the vendor specific extensions from TI are used. Basically there are:

  • Commands sent by the application
  • Events generated either directly as response to a command or indirectly i.e. when something is received

For technical reasons, the application consists of two threads. One handles the commands, which are enqueued in a FIFO queue and sent to the controller and one thread, which handles the events. My assumptions are that:

  • There is no specific order how events arrive.
  • Commands can fail when the internal state of the controller has changed and is out of sync with the application (i.e. a connection handle is not valid anymore)

Is this right ? Or is there some recommended way how this could be prevented ? I ask for the following reasons. I want to establish a link to a device. However when the link has not been established after some time, I cancel the request. If the above is true, it could happen, that the link is still established, so I need to handle this somehow.

Best regards,
Stefan

  • 0
    TI__Mastermind 34660 points
    Hello. So you want to use the CC2541 as a network processor? I don't really understand your concerns. In the example you describe where you want to cancel the link request, you can just send a link terminate command. This will return an event if the link was successfully terminated. If the link is established before it was able to be terminated, you will receive a link established event followed by an "unable to terminate" event. This is because a special connection handle is required in order to terminate a connection request and will thus fail if a connection is already established. See the GAPCentralRole_TerminateLink() in the GAPRoleCentralAPI of the software developer's guide for more information:

    www.ti.com/.../swru393

    FYI that guide is for the CC2640 but the API's and all profile / application information still apply for the cc2541.

    In terms of how to implement a network processor, there are generally two methods:
    - use the network processor project (HostTestRelease). In this scenario, you will be using the Bluetooth spec defined HCI interface. This will require your host processor to act as the profiles / application. Advantage: interface is already defined. Disadvantage: more host processor interaction needed since you need to implement the profiles and applicaiton.
    - modify an embedded project and add a custom UART / SPI interface to implement functionality. Advantage: less host processor interaction. Disadvantage: need to implement custom interface.

    When the device is acting as a peripheral, I would recommend the second solution. However, it sounds like your device will be acting as a central device since you are establishing connections. In this case, you will need to write a good deal of code regardless so I would recommend using the standard network processor project. As reference, there are some python examples here: processors.wiki.ti.com/.../CC254X_PC_Examples
  • 0 in reply to Tim C
    Prodigy 20 points
    Hello,

    yes actually it is a Rasbperry Pi like box with an integrated CC2541, which acts as a central device and needs to handle notifications from multiple other devices, which can be connected and disconnected dynamically by the user. I have no access to the firmware (I guess this is HostTestRelease) und some BTool-Logs. Since BlueZ seems not to be compatible I need to handle it myself and trying to get a overview. But what you said already gave me some valueable pointers. Thank you.

    Best
    Stefan