Do not know what value of RAM to configure after adding new characteristic to custom BLE service

[Xander To]

Hi Nordic team,

I'm using S132 with nRF52832 on my custom board. The SDK is nRF5_SDK_17.1.0_ddde560

I have made a custom BLE service that worked for several months. Now I want to add a new characteristic to my custom service. I know what to do in firmware as the new characteristic is 99% similar to the existing custom characteristic inside the custom service.

Firstly, my custom board crashed as expected because I didn't reconfigure the RAM space and 

NRF_SDH_BLE_GATT_MAX_MTU_SIZE in sdk_config. Therefore, I tested this firmware on DK to get the debug message (I currently don't have the hardware to debug the custom board so all debug tasks are on the DK). Initially, here are the RAM configurations on DK.

The original NRF_SDH_BLE_GATT_MAX_MTU_SIZE value is 1408. Based on the Segger IDE suggestion, I changed the RAM_START to 0x20002D30. I keep the NRF_SDH_BLE_GATT_MAX_MTU_SIZE  unchanged. The firmware works on the DK. I can see the new characteristic on my custom service. So that's good!

However, weird things started when I uploaded the same firmware on the custom board. The original RAM configurations of custom board are 

I know the original RAM configuration between DK and custom board are not the same but since they worked fine in the past, I didn't bother to match them together. But today, after I changed the RAM configuration on custom board to be the same as DK's configuration , the board crashes. Below is the custom board RAM configuration after the change

I thought it's probably the RAM change causing the crash. So instead of matching the RAM configuration of 2 boards, I increase the original RAM location up by 8 (0x20002D30 - 0x20002D28), similar to what I did on the DK. However, the board still crashes.

I tried changing the 

NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE to 1460. It still crashes.

I removed the BLE code in my firmware, it doesn't crash.

I added the BLE code back, but this time removed my new characteristic. It doesn't crash.

So that means my custom board is lacked of RAM to add the new characteristic and the amount of extra RAM required is not the same with the DK. Therefore, can you please give me a suggestion of what kind of RAM value I should change it to on the custom board? I program the DK with Segger IDE but program the custom board with GCC

Thank you for your help and suggestion.

Best regards,

Xander

[Einar Thorsrud]

Hi,

When you add more services or characteristics, the SoftDevice needs more RAM, which means that the application start address must be higher (and the size correspondingly smaller). The simplest way to do this is to increase the app start address significantly, and then adjust the RAM start address to what is calculated by the SoftDevice. See this post for details.

However, there are also other things that may need to be adjusted. What exactly happens when you write that the device "crash"? Have you debugged to see if there is a specific function call that returns an error? Sometimes it could be that you need to increase NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE in sdk_config.h and/or NRF_SDH_BLE_VS_UUID_COUNT (if adding vendor specific UUIDs). Note that if you do this, you also need to adjust the application RAM start address (and size).

[Xander To]

Hi Einar,

I currently don’t have the debugging hardware until next month so I’m trying to debug without a debug messege. I just add a new characteristic to my existing custom service (no new service is added compared to the previous firmware version) so do I still have to change the NRF_SDH_BLE_VS_UUID_COUNT.

I will try your suggest approach. However, I’m still very confused why DK and custom board using same firmware but require different RAM/ Flash configuration? I don’t know the debug message but I’m sure the error happens during the new characteristic being added to the service as commenting this section will result in no more crash.

Best regards,

Xander

[Einar Thorsrud]

Hi Xander,

Xander To said:

I currently don’t have the debugging hardware until next month so I’m trying to debug without a debug messege.

What about the tool you use to program? Or is that via DFU? (If you have some form of SWD programmer, that can typically also be used to debug).

Xander To said:

I just add a new characteristic to my existing custom service (no new service is added compared to the previous firmware version) so do I still have to change the NRF_SDH_BLE_VS_UUID_COUNT.

Then there is no need to adjust NRF_SDH_BLE_VS_UUID_COUNT (NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE could still be relevant, though).

Xander To said:

I will try your suggest approach. However, I’m still very confused why DK and custom board using same firmware but require different RAM/ Flash configuration?

If it is the exact same firmware, then you should not need to change the memory configuration. Is it the exact same firmware, or are there same changes? If so, what are those changes?

[Xander To]

Hi Einar,

I program the custom board with ST-Link and I cannot debug with ST-Link. I know I can debug the custom board by connecting to the DK pins, but I currently don’t have the wire to connect them together until next month. 
Yes, the firmware are exactly the same. I will double check this fact to ensure I didn’t mistakenly make any change between testing on DK and custom board.

Best regards,

Xander

[Turbo J]

OpenOCD should support debugging NRF52x chips with an ST-Link. Bit more difficult to set up than JLink, but doable.

RTT does not work with ST-Link though.