MTU size change then infinite reboot

[Jake]

I'm using nRF52DK and SDK12.2.0. Trying to change MTU size.

When I modified app_nrf_uart example as below

#define NRF_BLE_MAX_MTU_SIZE            103 

Then infinite reboot at below

#if (NRF_SD_BLE_API_VERSION == 3)
    ble_enable_params.gatt_enable_params.att_mtu = NRF_BLE_MAX_MTU_SIZE;
#endif
    err_code = softdevice_enable(&ble_enable_params);

softdevice_enable returns 0x04

Please help me to change MTU size.

[Petter Myhre]

It is probably returned from sd_ble_enable(). It means that you haven't provided enough RAM for the SoftDevice, because you increased the ATT MTU.

Examine softdevice_enable(), app_ram_base will tell you the required RAM start address for the application. Print it, or check it with the debugger (turn off optimizations).

[minswho]

I'm having the same problem. Did you ever figure out the solution?

[Petter Myhre]

I guess my answer below was the solution, since he accepted it. If that doesn't solve you problem I recommend adding a new question with your setup.

[minswho]

I'm just having a hard time finding the RAM start address you were talking about. Would you mind helping me with just that? I don't think a separate thread is necessary.

This is what I'm currently seeing from the debugger. https://goo.gl/YGrZS0

[Petter Myhre]

Of course. First turn off optimizations and recompile. Then go into softdevice_enable, there you see a function named sd_ble_enable(). If you put a breakpoint after this function is called you can check the value of app_ram_base to see what the RAM start address should be. The size should be 0x10000 - app_ram_base = size.