array size increase causes bluetooth to not connect.

[Robin]

Hello once again Nordic Pro's,

My latest issue, I believe to be related to stack/heap settings, but dont have enough information to track/correct.

I have a couple int array variables that, if their size is increased above 105 elements, bluetooth no longer connect to our central test board.

Not sure where to start chasing this  as I have no compile, build or load error messages, just a failure to connect.

Any help in chasing this down is greatly appreciated.

Device: 51822,

SDK: 12.3,

IDE: Keil 5.28,

App based on app_ble_uart peripheral.

Thanks again,

Robin @ TL

[Turbo J]

On the 16KB NRF51x variants, you can run out of RAM quite quickly.

Testing what is actually happening requires debugging, e.g. with a J-Link.

[tesc]

Hi,

Let me add that our SoftDevices has a maximum stack usage of around 1.5 kB. In other words, if at any time SoftDevice + application RAM usage + application stack usage exceeds 14.5 kB then you may get a stack overflow which will result in undefined behavior.

Debugging will either give you error codes, or, you can have a look at the stack pointer to see if it goes alarmingly high. Remember that each array of a hundred 32 bit integers is 400 bytes, not that far from half a kilobyte, so if you have 16 kB of RAM those arrays quickly takes up a significant portion of available RAM.

Also, how much RAM is available to the stack? (The way to tell in Keil is that ZI-data and RW-data is the total static ram used by the application, the rest of available RAM is for the stack.)

Are the arrays in static memory or are they also put on the stack?

How many arrays are there?

Regards,
Terje

[Robin]

Hello everyone,

According to the map file, I am well under RAM and ROM limitations.  There are only 2 arrays and they are both static as are most of the variables in our app.  W/r/t stack size it is define in the startup at 2048.  Any change to this in either direction causes the same result, not BLE connection.  So, where should I look when debugging, given no stack pointer overrun?

Thanks again

Robin @ TL

[Robin]

So, I have tracked this down to interference between the allocated stack and the softdevice RAM requirements.  Is there any way to get the exact or max, not min, RAM requirements for the softdevice in our app?

Thanks

Robin @ TL

[tesc]

Hi,

Maximum call stack usage by SoftDevice is 1536 bytes (0x600), according to SoftDevice Specification (see the section Memory resource requirements.) This is taken from the call stack which is shared between SoftDevice and application. See Memory resource map and usage, for details on how RAM is divided between MBR, SoftDevice, Application, Heap (if present) and Call Stack.

If you use the SoftDevice Handler library from nRF5 SDK v12, the call to softdevice_enable() will output the minimum APP_RAM_BASE if logging and DEBUG are enabled. If enabling the SoftDevice directly with sd_ble_enable() you can check the value pointed to by the p_app_ram_base argument after the call, as it gets updated with the minimum APP_RAM_BASE for the given SoftDevice configuration. In both cases, the rest of RAM (above APP_RAM_BASE) is for application, heap and call stack.

Regards,
Terje