ATtiny1614: micros() runs ~37.5% fast despite correct CPU clock

[Amaruq-code]

Update: root cause was choosing 'Internal Tuned' as the clock source. Switching to the plain 'Internal' clock restored correct timing (500 ms blink ≈ 1 Hz). UART output is being re-tested. Closing since this was a configuration issue.

[hmeijdam]

Looks to me you use the tuned option without having tuned the part first.
Try the default clock options (without the "- tuned" behind it)

https://github.com/SpenceKonde/megaTinyCore/blob/master/megaavr/extras/Ref_Tuning.md

[Amaruq-code]

I also measured the UART timing with an oscilloscope. With Serial.begin(9600), the transmitted bit width is approximately 60 µs instead of the expected 104 µs, corresponding to an actual baud rate of approximately 16.7 kbaud. This suggests the UART baud generator is also using an incorrect clock basis.

[hmeijdam]

Sure. If your oscillator is off because of using the "- tuned" option where you should not. Everything except the 32768 KHz Oscillator will have a wrong timing.

[Amaruq-code]

Thanks you were correct. Switching to the internal 5 MHz solved the problem. As you have probably guessed I'm fairly new to playing with these MCU using my own designed boards. There are lots of simple traps to fall into On Friday, August 7, 2026 at 09:07:00 PM GMT+12, Hans ***@***.***> wrote: hmeijdam left a comment (SpenceKonde/megaTinyCore#1287) Sure. If your oscillator is off because of using the "- tuned" option where you should not. Everything except the 32768 KHz Oscillator will have a wrong timing. Image: Image (view on web) — Reply to this email directly, view it on GitHub, or unsubscribe. Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS and Android. Download it today! You are receiving this because you authored the thread.Message ID: ***@***.***>