RE: Right way to keep a central up to date with infrequently changing peripheral data item

Hung Bui — Tue, 12 May 2020 14:12:29 GMT

Hi Chris,

You can update the value of the characteristic using the sd_ble_gatts_hvx () even when it's not connected. Here is the quote from the description of the function :

* @note The local attribute value may be updated even if an outgoing packet is not sent to the peer due to an error during execution.
* The Attribute Table has been updated if one of the following error codes is returned: @ref NRF_ERROR_INVALID_STATE, @ref NRF_ERROR_BUSY,
* @ref NRF_ERROR_FORBIDDEN, @ref BLE_ERROR_GATTS_SYS_ATTR_MISSING and @ref NRF_ERROR_RESOURCES.
* The caller can check whether the value has been updated by looking at the contents of *(@ref ble_gatts_hvx_params_t::p_len).

Both of your options of either do a read at the beginning of the connection or do a notification instead are both good. The option to do a read is preferred in my opinion because you don't have to implement any code on the peripheral side. You only need to allow read permission to the characteristic. The task to read should be done on the central side.