Run a standard Zephyr application in NRF5

[giansta]

I have a sample application running in standard Zephyr 3.2.99. The application is just looping doing a sleep (k_sleep(K_SECONDS(10))) and logging a line.

I tried to build it to be run in nRF with MBR, Sofdevice (disabled) and bootloader. This will not be the system definitive app, just a special purpose one that would be convenient to be a Zephyr app.

To build it I took care of different memory layout: flash load offset 0x26000 (then changed to 0x1000), and reserving first 0x3000 RAM addresses that could be used by Softdevice.

When started by the Nordic bootloader, it correctly loops for >= 250 seconds (regardless of k_sleep interval, e.g. 10 or 30 sec), then it stops logging.

I tried doubling and quadrupling CONFIG_PRIVILEGED_STACK_SIZE and CONFIG_MAIN_STACK_SIZE (then even CONFIG_ISR_STACK_SIZE and CONFIG_IDLE_STACK_SIZE).
I checked usage of SVC interrupts, yet they seem unused bot in nFR and in zephyr. Then I investigated debugging, it looks like the last k_sleep call is waiting for a PendSV exception in arch_swap().

It's not clear to me why the PendSV interrupts are coming fro ~4 minutes and they stop. I read the S132 SoftDevice Specification and I couldn't find a valid reason why this should happen.

I thought about a possible incompatibility with Sofdtdevice and then I moved the app from 0x26000 to 0x1000 and I was surprised that the issue is the same.

The bootloader sets the vector table address for Sofdevice and now my app is in place of SD at 0x1000, so I would expect that the interrupts are forwarded (not only for 4 minutes).

Any suggestion is welcome.

Thanks,

Giancarlo.

[giansta]

Hello. I did some further tests.

First, as Vidar mentioned in Quentin's ticket 298651, I checked the VTOR register logging its value at application start.
It has the correct application address, that is 0x26000 or 0x1000, depending on where I locate it. As expected, nothing changes re-writing it.

Second, I would highlight the timings: the time when the k_sleep() call waits forever instead than 10 seconds happens after ~ 4 minutes (00:04:22 last log time). After that, the Zephyr timeout function sys_clock_announce() is called exactly every 4 minutes 16 seconds, that is half of the 24-bit timeout in nrf_rtc_timer: this is a good coincidence.
I verified that the RTC interrupts happen as expected every ~ 8 minutes and 32 seconds.
I'm trying to investigate what can happen differently (register values or whatever) when started by nRF5 bootloader instead of MCUboot.

Perhaps you may have some advice.