haukepetersen opened a new issue #879:
URL: https://github.com/apache/mynewt-nimble/issues/879


   While doing a sequence of energy measurements, I noticed some strange 
behavior on the `nrf52840dk` (`nrf52840`). While running a simple application 
that sends out legacy advertisements every 500ms, I can see CPU activity 
between two advertisement events where there should be none. This happens in 
non-deterministic intervals.
   
   Trace A (ADV interval: 500ms, payload 3 byte, non-connectable, 
non-discoverable):
   
![ppk_nrf52840_adv500ms_NON](https://user-images.githubusercontent.com/620834/97680258-b6d8a500-1a96-11eb-8f2d-c57793d6168c.png)
   
   Trace B (ADV interval: 500ms, payload 3 byte, undirected-connectable, 
general discoverable)
   
![ppk_nrf42840_adv500ms_UND](https://user-images.githubusercontent.com/620834/97680583-35354700-1a97-11eb-85ff-3e6541c98143.png)
   
   Running the exact same application on the `nrf52dk` (`nrf52832`) does not 
show this behavior, on that board the trace looks as expected. So from that I 
think this might be a PHY related issue on the `nrf52840`?!
   
   I also wonder if this could be related to #767?
   
   Background infos:
   - running NimBLE (dba097972d28701c10b9af2a48af7d924c9cfca3) @ RIOT 
(35b6ccedf31f10a5f8e4f97609ad5b10c28bdc34)
   - the application simply calls `ble_gap_adv_start()` with the following 
params:
   ```
   struct ble_gap_adv_params adv_params = {
           .conn_mode = BLE_GAP_CONN_MODE_NON, // or BLE_GAP_CONN_MODE_UND for 
trace B
           .disc_mode = BLE_GAP_DISC_MODE_NON,  // or BLE_GAP_DISC_MODE_GEN for 
trace B
           .itvl_min = BLE_GAP_ADV_ITVL_MS(500),
           .itvl_max = BLE_GAP_ADV_ITVL_MS(500),
       };
   ```
   - No additional (user) threads 
   - NimBLE is configured as stated in `porting/targets/riot/syscfg.yml` with 
the following changes:
   ```
   CFLAGS += -DMYNEWT_VAL_BLE_LL_TX_PWR_DBM=0
   CFLAGS += -DMYNEWT_VAL_BLE_LL_MAX_PKT_SIZE=251
   CFLAGS += -DMYNEWT_VAL_BLE_LL_CFG_FEAT_DATA_LEN_EXT=1
   CFLAGS += -DMYNEWT_VAL_BLE_L2CAP_COC_MPS=200
   ```
   


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