[bug] Program crashes when SPI.begin() is called before setup()

[Alejandro-Casanova]

Hardware

Seeed Studio XIAO MG24

Core version

3.0.0

Arduino IDE version

2.3.7

Operating system

Windows 11

Radio stack variant

No radio

OpenThread Border Router device (if using Matter)

No response

Issue description

When running SPI.begin() before setup, the program crashes.

For context: I'm using mcp2515 library which makes this call inside the main class constructor. For this reason, just instantiating the main MCP2515 class as a global object will trigger the call to SPI.begin(). This library is popularly used, and instantiating it globally doesn't produce a crash on other Arduino stacks.

I prepared a minimal example emulating what I describe.

Serial output

When SPI.begin() is called during setup, minimal example program works as expected:

Running loop...
Running loop...
Running loop...
Running loop...

When SPI.begin() is called before setup, program crashes and there's no serial output.

RTT output (if using Matter)

No response

Minimal reproducer code

The following code produces the crash:

#include <Arduino.h>
#include <SPI.h>

class foo
{
public:
    foo() {
        SPI.begin();
    }
};

foo myFoo;

void setup()
{
    Serial.begin(115200);

    // SPI.begin();
}

void loop()
{
    Serial.println("Running loop...");

    delay(1000);
}

The following code runs with no problems:

#include <Arduino.h>
#include <SPI.h>

void setup()
{
    Serial.begin(115200);

    SPI.begin();
}

void loop()
{
    Serial.println("Running loop...");

    delay(1000);
}

[silabs-bozont]

Hello Alejandro Casanova (@Alejandro-Casanova),
Unfortunately this is an expected behavior on Silicon Labs boards. The peripherals and their clocks are initialized in the main() function by design of the underlying SDK. If you call any peripheral related function before it (like in a global instance's constructor) it'll meet with an uninitialized peripheral and crash.
I've added some guards for the GPIO before to avoid crashing - perhaps the SPI/Wire library can include those as well.
However that'll not solve the issue - just silently ignore the calls before init - which could make debugging harder if you're not aware of this.

To work this limitation around you can instantiate your library during setup() to have everything initialized before:

#include <Arduino.h>
#include <SPI.h>

class foo
{
public:
    foo() {
        SPI.begin();
    }
};

foo* myFoo;

void setup()
{
    Serial.begin(115200);
    myFoo = new foo();
}

void loop()
{
    Serial.println("Running loop...");
    delay(1000);
}

[Alejandro-Casanova]

Tamas Jozsi (@silabs-bozont) Thank you for your reply! I wasn't aware of this limitation of the underlying SDK. I'll have it in mind from now onwards.

[silabs-bozont]

Glad I could help! Closing this one, feel free to open another one if you have other issues!