Raspberry Pi Pico board using multicore lib with mbedOS - two interesting observations

I'm using a Raspberry Pi Pico board with the ArduinoCore-mbed 2.1.0.

I'm experimenting with the multicore library, which is part of the pico-SDK and I am using a mix of Arduino commands and mbedOS commands.

**Observation 1**: CORE1 does not like the standard `delay()` or the `sleep_ms()` function within a while loop.

For example this does not work:
```
void core1_entry() {
// Note using mbed command mbed::DigitalOut led2(p2, 0); to define my led GPIO
while (1) {
sleep_ms(1000);
led2 = !led2;
}
}

```

But if I use millis() as a timer function within Core1 it does work:

```
void core1_entry() {

uint32_t t_int = millis();

while (1) {
if ((millis() - t_int) > 1000) {
led2 = !led2;
t_int = millis();
}
}
}
```

So this code works for me:

```
#include
#include "pico/multicore.h"

mbed::DigitalOut led1(LED1, 0);
mbed::DigitalOut led2(p2, 0);

void core1_entry() {

uint32_t t_int = millis();
while (1) {
if ((millis() - t_int) > 1000) {
led2 = !led2;
t_int = millis();
}
}

}

void setup() {

multicore_launch_core1(core1_entry);

}

void loop() {
led1 = !led1;
sleep_ms(500);
}
```

**Observation 2**: multicore does not like the mbedOS EventQueue function.

First I tried using EventQueue in CORE0, and I found that only one core works and this depends on the order you place things. For example, with this code only Core 1 works:

```
#include
#include
#include "pico/multicore.h"

using namespace std::chrono_literals;

mbed::DigitalOut led1(LED1, 0);
mbed::DigitalOut led2(p2, 0);

events::EventQueue queue;

void eventTriggerHandler()
{
led1 = !led1;
}

void core1_entry() {

uint32_t t_int = millis();

while (1) {
if ((millis() - t_int) > 1000) {
led2 = !led2;
t_int = millis();
}
}
}

void setup() {

multicore_launch_core1(core1_entry);

// events are simple callbacks, call every 500 milliseconds
queue.call_every(500ms, eventTriggerHandler);

// the dispatch method executes events
queue.dispatch();

}

void loop() {
}

```

but if I change the order around so that `multicore_launch_core1(core1_entry); `is called after `queue.dispatch()` then only core0 works. As in:

```
void setup() {

// events are simple callbacks, call every 2 seconds
queue.call_every(500ms, eventTriggerHandler);

// the dispatch method executes events
queue.dispatch();

multicore_launch_core1(core1_entry);

}
```

But if I try and use the EventQueue method in Core 1 it causes a hardware crash. I added a Serial1.begin() in my Core0 setup() and it spits out this info

```
++ MbedOS Fault Handler ++

FaultType: HardFault

Context:
R0 : FFFFFFDC
R1 : 2000CD40
R2 : 2000CCFC
R3 : 20002A98
R4 : 00000828
R5 : 2000CD84
R6 : 10000343
R7 : 10002221
R8 : FFFFFFFF
R9 : FFFFFFFF
R10 : FFFFFFFF
R11 : FFFFFFFF
R12 : FFFFFFFF
SP : 20040F88
LR : FFFFFFF9
PC : 10001F90
xPSR : A100000B
PSP : FFFFFFFC
MSP : 20040F68
CPUID: 410CC601
Mode : Handler
Priv : Privileged
Stack: MSP

-- MbedOS Fault Handler --

++ MbedOS Error Info ++
Error Status: 0x80FF013D Code: 317 Module: 255
Error Message: Fault exception
Location: 0x10001F90
Error Value: 0x2000CB8C
Current Thread: rtx_idle Id: 0x2000CCFC Entry: 0x10004059 StackSize: 0x200 StackMem: 0x2000B9B8 SP: 0x20040F88
For more info, visit: https://mbed.com/s/error?error=0x80FF013D&osver=61000&core=0x410CC601&comp=2&ver=100300&tgt=RASPBERRY_PI...

-- MbedOS Error Info --

```

Reproduce the two observations on a Raspberry Pi Pico with ArduinoCore-mbed 2.1.0, starting from the provided core1_entry(), setup(), and EventQueue examples. Compare delay(), sleep_ms(), millis(), and queue.dispatch() behavior, then use the captured MbedOS HardFault output to identify the failure boundary. Done means documenting the cause and confirming a compatible multicore/EventQueue behavior or a scoped fix.

Written by the indexing model from the issue text.