[bug] slow delay() and millis() when 32768 Hz XTAL is not connected to PD0 and PD1

[lyusupov]

Hardware

EFR32BG22

Core version

2.1.0

Arduino IDE version

any

Operating system

any

Radio stack variant

No radio

OpenThread Border Router device (if using Matter)

No response

Issue description

this is a follow up for the thread: #80 (comment)

when 32768 Hz XTAL is not connected to PD0 and PD1 pins -

• delay() and delayMicroseconds()
• millis() and micros()
  are operating approx. 100-110 times slower than they should.

I found out that the Core relies heavily on the external 32.768 kHz XTAL. It assumes that it is a mandatory hardware component.
However, this requirement is not specified in the Limitations section of the Core's README:
https://github.com/SiliconLabs/arduino#limitations

The request is:

Is it possible to avoid using of the RTC timer for the purpose of Arduino delay() ... and millis() ... functions in the future releases of the Core ? Arduino Cores for other SoCs typically don't do that.

Serial output

No response

RTT output (if using Matter)

No response

Minimal reproducer code

No response