[GZP] Two gazelle "slaves" pairing with each other

[Jakub]

Hello,

I have two identical devices with Laird's BL600 chip (that uses NRF51822). They are initialized as NRF_GZLL_MODE_DEVICE and use GZP library (without encryption - only pipe no 2 is used). They are cyclically calling gzp_address_req_send() function until the positive response is returned. And if no host is nearby, they can pair with each other! So that the data sent from one device is read by another (and vice versa). How is it possible? Is it any known issue?

Unfortunatelly I don't have a direct access to the chip to connect with a PC and debug it. I only have the code and can observe its behavior, which is unambiguous. Of course the devices are designed to communicate with a host at normal operation, but I think such behavior should not be possible anyways.

[Hung Bui]

Hi Jakub,

You are talking about a product that you are evaluating, not a product that you are creating ? And the behavior that you described is what you observed and you want to explain it ?

There are many things can be implemented to achieve that. They may use another protocol to talk to each other.

Two Gazell slaves won't be able to talk to each other. But they may use other protocol for example ESB, or they may switch role, or they broadcast data, many way I don't know.

You should better get information from the owner of the devices than just guessing like this.

[Jakub]

Hello and thank you for a quick response.

I'm talking about the product that was developed by an external company and now I took over it. So I have a ready product and the code for it, but no insight in the development process itself. I have observed this strange behavior and yes, I want to explain it - as the code seems to be quite a standard usage of gazell pairing library and there's no other protocol implemented (apart from possibility of flashing the module via BLE, but that is disabled when in Gazell mode).

I know it is not easy to just "guess" what's wrong, but I'm not sure what more information can I provide apart from the full code. I hoped that maybe somebody had a similar experience by any chance. Can it be there's a bug in an older version of Gazell library?

[Hung Bui]

Hi Jakub,

If you have the source code and you can compile it, you can just flash it to nRF51 Development Kits and test. Then you can step through the code and print debug log. You may need to disable any external peripheral dependency in the source code to make it run on the NRF51 DK.

But again, as far as I know 2 slaves shouldn't be able to talk/pair to each other .