Unknown function at <address> starts executing during the ISR's execution</address>

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Thu, 03 Jun 2021 07:08:53 GMT

Hi,

[quote user="morpho"]Mind elaborating on what your initial request was then? Doesn't MSP tell you the start address?[/quote]

I was referring to the start address of the application in flash as a simple way to know if you use a SoftDevice. If you application starts at 0x0, you do not. If it starts at 0x1000 you are probably using the MBR only. If it start at something higher than that you are probably using a SoftDevice (which includes the MBR).

[quote user="morpho"]Is 0x774 the SVC number?[/quote]

No, it is within the interrupt forwarding table. It seems to be for UART0/UARTE0 (UART0_UARTE0_IRQHandler), which is enabled by default in the example project for UART logging.

[quote user="morpho"]where's sd_softdevice_enable located? i can't seem to find it in my application[/quote]

If you are still using ble_app_hrs_freertos() and have not removed large parts of the code, then you call sd_softdevice_enable() indirectly from ble_stack_init() by calling nrf_sdh_enable_request() (see implementation in <SDK>\components\softdevice\common\nrf_sdh.c).

RE: Unknown function at
starts executing during the ISR's execution

morpho — Wed, 02 Jun 2021 21:12:52 GMT

[quote userid="7377" url="~/f/nordic-q-a/75739/unknown-function-at-address-starts-executing-during-the-isr-s-execution-address/313204#313204"]

MSP, as mentioned earlier, at the start of the application is 0x20040000, which according to your description, means I'm using a SoftDevice?

No.

[/quote]

Mind elaborating on what your initial request was then? Doesn't MSP tell you the start address?

> The SoftDevice inspects the SVC number, and if it is equal or greater than 0x10, the interrupt is processed by the SoftDevice.

Is 0x774 the SVC number?

> The SoftDevice uses the first eight bytes of RAM when not enabled. Once enabled, the RAM usage of the SoftDevice increases. With the exception of the call stack, the RAM usage for the SoftDevice is always isolated from the application usage. Therefore, the application is required to not access the RAM region below APP_RAM_BASE. The value of APP_RAM_BASE is obtained by calling sd_softdevice_enable

where's sd_softdevice_enable located? i can't seem to find it in my application

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Wed, 02 Jun 2021 18:25:00 GMT

[quote user="morpho"]MSP, as mentioned earlier, at the start of the application is 0x20040000, which according to your description, means I'm using a SoftDevice?[/quote]

No.

[quote user="morpho"]I'm building stuff on top of ble_app_hrs_freertos[/quote]

That project uses the SoftDevice, and thus MBR. Then we can conclude that 0x774 is from the interrupt forwarding code in the MBR, so all seems good.

RE: Unknown function at
starts executing during the ISR's execution

morpho — Wed, 02 Jun 2021 16:50:52 GMT

MSP, as mentioned earlier, at the start of the application is 0x20040000, which according to your description, means I'm using a SoftDevice?
I'm building stuff on top of ble_app_hrs_freertos project. And I agree with you on learning about the softdevice architecture itself.

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Wed, 02 Jun 2021 07:35:44 GMT

Hi,

[quote user="morpho"]Sorry, you didn't seem to answer my dumb question: how do you verify if the softdevice is being used on my device?[/quote]

What is the start address of your application? If it is at 0x0, then you are not using MBR or SoftDevice. If it is higher than that, you are typically using the SoftDevice (even if it is not enabled, it will forward interrupts to your application). If you let me know which example project you have based your app on I can check for you. To be frank I think you need to read up a bit on the overall architecture before digging into such details as it seems to me you may be missing the over all understanding that should be in place first.

Update: I see i referred to 0x744 instead of 0x774 and that typo stuck in this thread. However, both are within the interrupt forwarding code of the MBR, so that is certainly what is going on.

RE: Unknown function at
starts executing during the ISR's execution

morpho — Wed, 02 Jun 2021 07:14:59 GMT

[quote userid="7377" url="~/f/nordic-q-a/75739/unknown-function-at-address-starts-executing-during-the-isr-s-execution-address/313015#313015"]It is only "reset" when the first task starts. After that, it behaves just as normal stack. I am not sure what you want to verify, but you can check the stack pointer from the debugger.[/quote]

Yeah but that's what I'm trying to do: to figure out how to actually see this behavior by navigating MSP. As described, the initial value is `0x20040000` at the start of main. Is it supposed to reset back to `0x20040000` once the task starts?

Sorry, you didn't seem to answer my dumb question: how do you verify if the softdevice is being used on my device?

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Wed, 02 Jun 2021 07:05:14 GMT

[quote user="morpho"]Do you know how to verify the resetting of MSP? Initially when I run the program, it's set to `0x20040000` and when the IRQ is fired, it doesn't reset back to the same address[/quote]

It is only "reset" when the first task starts. After that, it behaves just as normal stack. I am not sure what you want to verify, but you can check the stack pointer from the debugger.

[quote user="morpho"]Is this is the .hex file located under components\softdevice\SoftDevice\hex?[/quote]

Yes (though the path is a bit different with different variants). All BLE projects use the SoftDevice.

[quote user="morpho"]I'm using Segger IDE and this link only has info on other IDEs.[/quote]

This is independent of which IDE / toolchain you use.

[quote user="morpho"]But all i'm doing is using one of the freertos apps and making changes on top of it, and running/debugging it[/quote]

There are several example apps in the SDK, both using a SoftDevice and not using it. Please check if you are using a SoftDevice (and thus MBR) or not, as that is key to know if 0x744 is within something we provide (the MBR) or the app you built yourself. If it is in the MBR as I assumed, it is in the interrupt vector table, so related to interrupt forwarding. See Exception model in the SoftDevice specification.

RE: Unknown function at
starts executing during the ISR's execution

morpho — Wed, 02 Jun 2021 00:00:50 GMT

> That is how this is typically done in FreeRTOS (see this thread). You can modify vPortStartFirstTask() in port.c to not reset the stack pointer if you want to avoid this, or simply make sure to not put any data you will rely on after starting the scheduler on the stack.

fair. So it's more of a design thing to reset the MSP once the scheduler runs. Do you know how to verify the resetting of MSP? Initially when I run the program, it's set to `0x20040000` and when the IRQ is fired, it doesn't reset back to the same address

[quote userid="7377" url="~/f/nordic-q-a/75739/unknown-function-at-address-starts-executing-during-the-isr-s-execution-address/312982#312982"]I have assumed that you are using the MBR (implicitly if you are using the SoftDevice), but I did not get that confirmed. Do you use the SoftDevice? If so 0x744 is within the MBR and I will check tomorrow and get back to you. (If not, then 0x744 is within your application and I cannot say what is located there).[/quote]

Is this is the .hex file located under components\softdevice\SoftDevice\hex? I'm using Segger IDE and this link only has info on other IDEs. But all i'm doing is using one of the freertos apps and making changes on top of it, and running/debugging it

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Tue, 01 Jun 2021 21:24:21 GMT

Hi,

[quote user="morpho"]That's all I'm trying to clarify - how come does scheduler "wipe out" the stuff on the main stack as soon as it runs that those instances aren't accessible elsewhere be it in the ISR?[/quote]

I see. That is how this is typically done in FreeRTOS (see this thread). You can modify vPortStartFirstTask() in port.c to not reset the stack pointer if you want to avoid this, or simply make sure to not put any data you will rely on after starting the scheduler on the stack.

[quote user="morpho"]In addition to what's asked above, I'm curious to see how to actually know what is causing the issue by understanding what does unknown function at 0x744 refer to[/quote]

I have assumed that you are using the MBR (implicitly if you are using the SoftDevice), but I did not get that confirmed. Do you use the SoftDevice? If so 0x744 is within the MBR and I will check tomorrow and get back to you. (If not, then 0x744 is within your application and I cannot say what is located there).

RE: Unknown function at
starts executing during the ISR's execution

morpho — Tue, 01 Jun 2021 17:32:53 GMT

Sorry for the confusion. If you have something like the following, the stuff on the stack won't get cleared or overwritten though...whereas if you had a scheduler running before the while loop, according to you and what i've read, the main stack will get overwritten by, say, ISR if it were to fire.

int main(void) {

   Uart uartObj;
   int variable = 5;
   
   while(1);
}

That's all I'm trying to clarify - how come does scheduler "wipe out" the stuff on the main stack as soon as it runs that those instances aren't accessible elsewhere be it in the ISR? That's probably what's causing my issue because I'm accessing a Uart instance inside an ISR whereas the instance itself is defined in main.

- In addition to what's asked above, I'm curious to see how to actually know what is causing the issue by understanding what does unknown function at 0x744 refer to

- nRF5_SDK_17.0.2_d674dde

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Tue, 01 Jun 2021 06:59:29 GMT

Hi,

I am not sure I understand the question. Just to be clear data in the stack is overwritten after it is no longer used and the same region can be used again (think of the stack pointer going up and down, up and down etc. depending on the stack usage). You will note corrupt anything on stack by using more stack, other than things that have gone out of scope. There is no difference here compared to other use cases where you do not use FreeRTOS (when we look at the system stack and ignore each tasks stack).

I have a few question:

Do you ask about what is at 0x744 because there is an issue or because of curiosity? If the former please elaborate on the issue.
Which SDK and SoftDevice version are you using?

RE: Unknown function at
starts executing during the ISR's execution

morpho — Mon, 31 May 2021 17:49:13 GMT

So ISR uses the same kernel/main stack so it starts overwriting as soon as it's called. How do you verify this behavior? Do you see if MSP, when the interrupt is fired, starts at the base address of the kernel stack?
Clarifying because I have some instances of the peripheral defined inside main before the scheduler is called

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Mon, 31 May 2021 17:41:18 GMT

Looking at your screenshot I assume you refer to the FreeRTOS scheduler. The stack will not be explicitly wiped out, no. However I believe the main stack is used for ISRs etc, so part of the data will be overwritten at some point.

RE: Unknown function at
starts executing during the ISR's execution

morpho — Mon, 31 May 2021 16:47:27 GMT

Can you confirm if the scheduler wipes out the stuff allocated on the stack inside main once it runs?

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Fri, 28 May 2021 17:15:35 GMT

Hi,

The MBR is the master boot record. It is the first page of the SoftDevice. Execution should not get "stuck there". How did you end up here when debugging? As interrupts are forwarded by the SoftDevice I wonder if it could be simply that you are stepping through code execution also when it is outside your application binary, but that is just a guess.

RE: Unknown function at
starts executing during the ISR's execution

morpho — Fri, 28 May 2021 16:04:12 GMT

What's exactly MBR? Why is it getting "stuck" on here then once the interrupt is fired?

RE: Unknown function at
starts executing during the ISR's execution

Einar Thorsrud — Fri, 28 May 2021 12:03:06 GMT

Hi,

This is within the MBR. The MBR forwards interrupts to the SoftDevice, which forwards them to your application. I am not sure what you mean by sleep mode? (If the CPU is executing code, it is not in sleep at that instant).

Unknown function at <address> starts executing during the ISR's execution</address>

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RE: Unknown function at
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