Application stack overflow during SoftDevice execution

Question

Chip: nRF52832 
 SDK: 15.0.0 
 SoftDevice: S132 6.0.0 
 IDE: IAR EWARM 8.30 
 I have a peripheral-role application with __ICFEDIT_size_cstack__ = 0x800 (application call stack size set to 2048 bytes). What I'm seeing on occasion is very shortly after establishing a connection with a central device, the runtime stack overflows beyond the 0x800 byte bounds and starts overwriting static variables in my application. I have set memory breakpoints which hit when the stack overflows, and I can see my data has corrupted. I also can see the stack pointer register showing a value outside the stack bounds. 
 When the breakpoint hits, the function call stack in IAR simply says: [__checksum_value + 0xeee7], which from my understanding means that code execution is within the soft device and not within my application. Another intersting thing that I'm seeing when I look at the raw data that is being written to the stack includes values that appear to be RAM addresses within the space allocated to the soft device. For example, I see values such as 0x2000289C and 0x20000918 written repeatedly, and my __ICFEDIT_region_RAM_start__ (APP_RAM_BASE) is set to 0x20004048 meaning that any values between 0x20000000 and 0x20004048 are allocated for the soft device to use. I know that my APP_RAM_BASE is set correctly because if I set it lower then I get an error response to the call to sd_ble_enable in in nrf_sdh_ble_enable. 
 Am I correct that the soft device is writing data on the application runtime stack? And if so, why would this happen? I have used IAR's stack usage analysis features and know that my max call chain is less than 2048 bytes, so I can't figure out what could be causing this stack overflow. 
 Thanks.

Turbo J · Accepted Answer

swlnk said: I have used IAR's stack usage analysis features 
 These cannot see how much stack the softdevice uses, because it is not compiled with your applicartion. 
 But the SD internal stack usage is documented (in the softdevice specifications) to be 2KB. With your on apps <=2KB stack usage, I would set up 4KB or 0x1000 bytes for stack.

swlnk · Answer

Hi Matt! This was from a couple of years ago so I don't remember all of the details, but I think the key point here (that I didn't realize when I wrote the question) is that the soft device and the application are sharing the same runtime stack. The "memory resource requirements" page in the soft device spec gives guidance on how much call stack usage you can expect from the soft device. You then need to look at your application and consider whether you have set the boundary to be large enough to handle the soft device "worst case" plus your application "worst case". In my application, the stack size was too small to handle this, and at times it would overflow causing corruption of my static variables. Simply increasing the stack size resolved the issue. My guess is that you are seeing something similar.

Application stack overflow during SoftDevice execution

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