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CC2538: ZNP does not pick up best channel when forming network

Patrick Wu
Prodigy 50 points

Part Number: CC2538
Other Parts Discussed in Thread: Z-STACK, CC2592

We are using CC2538 ZNP (Z-Stack Home 1.2.2a.44539) together with Linux Gateway.

In f8wConfig.cfg, default channel list is 0x02108800  (11, 15, 20, 25), this is the same as gateway config file (config.ini).

We flash the Firmware every time (to clear the NV) and bring our board to different environment to test, it seems network always started with channel 11, despite it is the worst in some case (strong wifi interference and retries). We are expecting a better channel selected by ZNP. 

Is this the correct behavior or we are not correctly using the configuration.

Thanks & Regards.

  • 0
    Guru 735695 points
    You can try to use SmartRF Studio to output continues TX signal on channel 11 and see if Coordinator would select other channel.
  • 0
    TI__Mastermind 35070 points
    Hi,

    Flashing the device does not mean NV is cleared (please see section 3 of Z-Stack Home Sample Application User's Guide.pdf, located in <Z-Stack install>/Documents).

    Although Zigbee and Wifi use 2.4GHz, they may operate on different channels.
    Channel 11 on Zigbee uses 2405 MHz, while Wifi can possible range from 2412 MHz to 2484 MHz.



    Regards,
    Toby
  • 0 in reply to YiKai Chen
    Prodigy 50 points

    Hi YiKai,

    Thanks for your suggestion. Tried with both Continuous Tx and Packet Tx (short interval) on channel 11 before start network, the ZNP was able to choose another channel, it works in this scenario.

    But I assume the MAC layer is using CCA to decide the starting channel, seems it is not effective when only coexistent with WiFi network (no other Zigbee Tx Source). Attached are SmartRF studio Continuous RSSI graph for channel 11 and channel 25 in my environment. Channel 11 is much noisy than channel 25 from the reading, but ZNP still choose channel 11 at startup.

    BTW, our module has CC2592 on board, I enabled 'HAL_PA_LNA' and 'HAL_PA_LNA_CC2592' macro when build ZNP firmware.

    Thanks & Regards!

  • 0 in reply to Patrick Wu
    Guru 735695 points
    I suppose you can skip channel 11 to form network if you think it’s noisy.
  • 0 in reply to YiKai Chen
    Prodigy 50 points
    Hi YiKai,

    I was thinking the z-stack could auto select a less noisy channel in this scenario (only coexistence with WiFi) without using another tool, but seems we have to rely on other measure to make it work.

    Thanks & Regards!
  • 0 in reply to Toby
    Prodigy 50 points
    Hi Toby,

    I am using a full binary image (512KB) to program the device, the NV pages should be cleared to 0.
    For channel selection, I was expecting a better channel (less noisy based on RSSI) to be auto selected by the stack, but seems we have to manually set it based on site survey to avoid interference by WiFi network.

    Thanks & Regards!
  • 0 in reply to Patrick Wu
    Guru 735695 points
    Obviously, the Z-Stack scan doesn't think the channel is noisy enough.
  • 0 in reply to YiKai Chen
    Prodigy 50 points

    OK, I understand, thanks very much for help!