NRF52840 high throughput with custom service error changing mtu

[superdan1]

Hi,

I'm using the NRF52840 Preview DK and want to create my own BT stack with high throughput between NRF52 and other BT devices.

As base I'm using the ble_app_template of nordic examples, created a BT Profile with help of Bluetooth Developer Studio from Bluetooth.com (https://www.bluetooth.com/develop-with-bluetooth/developer-resources-tools/developer-kits/bluetooth-starter-kit)

Now I have a profile including: heartrate service, batterylevel service, device information service and one custum service with two characteristics. (1. read/write, 2. notify)

I used the ble_app_att_mtu_throughput example of nordic to expand my own project. All works fine, since I don't change my NRF_SDH_BLE_GATT_MAX_MTU_SIZE of 23, and notification payload of 20 bytes.

The Problem now:
I want to incese the mtu size and enable the datalength extension (like in throughput example), while using the same methods "gatt_mtu_set(...) , data_len_ext_set(...). But every time I increse the MTU size, an other error occur. 

Set the MTU size to 50: one characteristic of my custom service disappears. Set the MTU size to 80: 3 services disappears. (Disappearing in nrfConnect App while scanning) Set the MTU size to 247: programm crashing in main loop.

I my opinion it looks like a memory problem, but I don't really know how to fix it. I already changed the flash/start/size, ram/start/size like in the throughput example (I think the maximum: FLASH_START=0x22000, FLASH_SIZE=0xfffff, RAM_START=0x200030d0, RAM_SIZE=0x3CF30).

I'm using Segger Embedded Studio on macOS for developing.

Anyone got an idea?
Thanks alot!

[ketil]

Hi,

This is strange behavior. Could you please zip your project files and attach them to this case so we can debug? If your code is sensitive we recommend you click on the GO PRIVATE button before uploading.

Ketil

[superdan1]

Hi Ketil,

I don't know how to set this case to private and upload my files?

[karthikeyan]

hi,

  where is the go private button

[superdan1]

After spotted a thread about NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE in DevZone (https://devzone.nordicsemi.com/f/nordic-q-a/30852/data-length-extension-causes-nrf_error_no_mem-on-services-init)
I found a solution for my problem.

Like I suspect it's a memory problem.

I increased the NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE (randomly, no calculation) of 1408 to 8KB (8192) and then the application runs with MTU size of 247 without any errors.

Of course I increased the ram_start value and adjusted the ram_size value of the application too. My values are now: 

Physical ram size minus ram_start size = ram_size.

The ram_start size is shown while debbuging in ble_stack_init() method in line err_code = nrf_sdh_ble_enable(&ram_start); 
Just read the &ram_start variable.

RAM_START=0x20004800
RAM_SIZE=0x3b800

Apparently there's no fix way to calculate the NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE, so just try out.

Daniel