program hangs on startup if not using microlib

[Bill Russell]

This is a general question I will throw out initially, but I can get more specific if necessary. This is something I see a lot in my year or so of development with nordic nRF5x chips. Sometimes I will run an application and it never gets to main(). Breaking in the debugger its hung in a loop somewhere, I assume in C startup. Checking "use microlib" will often fix this sort of issue. I also think that sometimes unchecking "use microlib" will fix the issue. Now, note that once I get my project configured and running things are fine. Usually its when I am upgrading the SDK or porting between nRF5x variants, etc, and my memory ranges might not be quite right or something. Can anyone think of reasons "use microlib" would fix this sort of issue.

[Jørgen Holmefjord]

MicroLib is optimized to use less code and data memory than using the ARM standard library. It should not affect the functionality of the code, as long as your program is compiled without errors and you flash the program correctly to the device. Have you tried debugging, to see where the code is stuck?

[Bill Russell]

it is stuck in a loop in an area with no source available, when I don't use microlib. If I use microlib then it runs fine. I am thinking its heap related (since full C library is said to use it), although my arm_startup_nrf52.s appears to have 8192 of heap defined.

[Jørgen Holmefjord]

Did you set optimization level to 0? Have you added something to your project that use heap? The softdevice and SDK should not use any heap.

[Bill Russell]

My understanding was that the full C library (non microlib) uses the heap.

[Jørgen Holmefjord]

As mentioned in the softdevice documentation, no heap is required by the softdevice. Also, from the ROM and RAM management tutorial: Heap memory can safely be set to zero as long as you don't use dynamic memory allocation (malloc/free). Note that heap is generally not used in our SDK examples. You are correct that using microlib will disable heap usage, but heap usage should not originate from the SDK examples.