CCCD change not written to flash after BLE Write (Server)

[KonstantinK]

Hello,

I am currently developing a firmware where I am acting as a server with nRF52840.

The protocol of my use case is:

1. Client is connecting to my device (server with bonding)
2. Client sets notification enabled (is written to flash by the server as PM_EVT_PEER_DATA_UPDATE_SUCCEEDED event indicates)
3. Client is writing to a custom characteristic
4. Client wants to set notification disabled (I receive the event that it is written to CCCD but I don't get the PM_EVT_PEER_DATA_UPDATE_SUCCEEDED event and nothing is written to the flash, since I want to store the information for reconnecting with the bonded device)

Do I have to handle the write to the CCCD on my own or could there be a problem with writing to my characteristic?

Note: When no write is executed, just notification enabling and disabling, everything works fine and is stored to flash.

best regards 

[Vidar Berg]

Hello,

It sounds like the bonding data is being erased on disconnect for some reason. It could be because the FDS storage is full as you indicated earlier and that  pm_handler_flash_clean()/pm_handler_flash_clean_on_return() is called. Or do you see the same if you do a full chip erase before you program your FW? 

FDS usage can be monitored with the fds_stat() function.

[KonstantinK]

Hello, thanks for your answer. I did some more research and debugging and discovered following:

I have 9 characteristic with a size of 510 bytes each. I have configured them with BLE_GATTS_VLOC_USER and it is not working (initializing and advertising works but writing to the characteristic causes problems with bonding data). When I configure them with a size of 201 bytes each (with NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE 1608), everything works fine (initializing, advertising and writing+bonding works). But as soon as I configure them with a size of 202 bytes, it is not working anymore. When I increase the NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE to 1700 bytes for example it is also working with a size of 202 bytes each. So the issue should be somewhere with my memory management and the size of NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE. My question is, when I am using the BLE_GATTS_VLOC_USER flag, why is the size of the characteristic still depending on the softdevice stack? And which NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE should i use for using such long characteristics?

Thanks for your help

best regards

[Vidar Berg]

Hello,

Would you mind trying with BLE_GATTS_VLOC_STACK instead?  The BLE_GATTS_VLOC_USER option was more relevant before when the attribute table size was not configurable. 

KonstantinK said:

But as soon as I configure them with a size of 202 bytes, it is not working anymore. When I increase the NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE to 1700 bytes for example it is also working with a size of 202 bytes each

I am surprised it helped to increase the NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE, to be honest. I would have expected the table size to remain unchanged since the attribute values are kept in the application memory. 

[KonstantinK]

Alright, I will try with BLE_GATTS_VLOC_STACK. Me too haha. Is there a maximum value for NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE, except the limitation of the ram?

[Vidar Berg]

Thanks. The max. table size is only limited by how much RAM you have to spare.