BT_SETTINGS CCCD creates more flash storage

[Sunil vignesh]

HI,

i have enabled CONFIG_BT_SETTINGS_CCC_STORE_ON_WRITE=y

so after power cycle the device automatically connects with iphone and the service also works fine

after this

I found that RAM flash memory

gets increase at every disconnect and connect

Example

I connect the device with nrf connect app desktop -> programmer

i read the device and found

flash NVM size  25 bytes from F8000

                          24 bytes from F8FF7.

after connected and paired with iphone 8 plus

flash NVM size  158 bytes from F8000

                          72 bytes from F8FF7.

again read the device

flash NVM size  195 bytes from F8000

                          104 bytes from F8FF7.

I need to work on DFU and also NVM flash storage to store 5KB data. My concern is because of this memory increase . where it get collapse or not

to memories the CCCD where only enable is memorize and disable is not to be memorize is it possible

because

when device is out of bound then it will disconnect at the time memory will increase and then in bound it auto connect and that also write .

i want to control this only write the enable function

2. How to delete the particular CCCD stored flash page

3. how to delete the pair bond stored flash page . peer bond data is controlled by softdevice

[Sigurd]

Hi,

I think the best way to solve this is to set CONFIG_BT_MAX_PAIRED to the max number of devices/Bluetooth bonds you want to support.
If you set CONFIG_BT_KEYS_OVERWRITE_OLDEST=y the Bluetooth Host will overwrite oldest keys with new ones if key storage is full.

[Sunil vignesh]

Hi Sigurd,

I have tried

Sigurd said:

CONFIG_BT_KEYS_OVERWRITE_OLDEST

and set max paired as 1.

program initaial shows 25 bytes storage

Mobile 1 paired 132 bytes   and delete bond from mobile phone 1

paired with mobile 2 and flash increase to 241 bytes .

it doesn't overwrite the previous flash area . i want to use that 132 bytes for all pairing devices . 

[Sigurd]

Looking at the documentation for NVS, https://docs.zephyrproject.org/latest/reference/storage/nvs/nvs.html it seem to be erased first when a sector is full.
"Elements are appended to a sector until storage space in the sector is exhausted. Then a new sector in the flash area is prepared for use (erased)."

Sunil vignesh said:

1 . if i set max_pair to be 1 when i connect second device it will over write  if i enable keys_overwrite_oldest?

 Yes, or marked it as invalid and erase it later when it needs the space.

Sunil vignesh said:

2. what will happen for CCCD flash writes how to over write the CCCD enable disable in same flash address

 You should not manually change this value from the application. The Bluetooth Host takes care of keeping this value correct.

Sunil vignesh said:

3. Is it possible to delete the pairing data from flash storage . and how?

 If you want to remove the bond/pair, use bt_unpair()

Sunil vignesh said:

before dfu the flash starts at 0xF8000 and now it starts at 0xFE000 why?

 Perhaps NVS started to use a new sector. The flash space reserved for storage can be found in the dts. E.g.

					storage_partition: partition@f8000 {
						label = "storage";
						reg = < 0xf8000 0x8000 >;
					};

[Sunil vignesh]

Hi Sigurd,

Yes, In board files .dts

having storage partition @f8000

0xf8000 -  0x8000

without dfu the peer bond date starts at f8000

and same config

while using dfu

the starting address is changed from f8000 to fe000

how it is happening

[Sigurd]

Each sector is 4kB, could be it needed to erase something, so therefore it stared to use a new sector (within the allocated area for NVS).