What can have changed to make an old project stop working for serial communication?

[AndKe]

I have a big Arduino build for Bluepill.
it uses three serial interfaces, one normal

#define MAVLinkSerial Serial1 << NORMAL
#define _HoTTSerial Serial2 << single pin, bidirectional
HardwareSerial Serial2(PA2);
#define _DEBUGSerial SerialUSB << CDC

this "always worked"
When receiving heartbeat on MAVLink, I should see a LED toggle.
On boot and on serial command the Debug interface should print.

I successfully compile the program, it uploads and runs fine (the startup LED animations etc works) then it just does not respond to serial commands on CDC, or seems to get the MAVlink heartbeat.

Is there anything you can think of that has changed - this is a stab in the dark.

[fpistm]

Don't know. Best option is to debug.

[fpistm]

What is the latest version where it works?

[AndKe]

I compiled it last about 6-9 months ago, and I do not know which libraries were updated since, I did blindly downgrade a few, one a t a time. without conclusive results.

After some debugging I finally found the utimerLib I use to get a function called at 20hz is the reason for the actual freezing.
https://github.com/Naguissa/uTimerLib

enabling this:
TimerLib.setInterval_us(timer20hzEvent, 50000);

frezes the uC aft a short while.
I have put a check for 50ms in the main loop (replacing int driven timer) - and everything started working fine again.

This library does not seem to have been updated in that timeframe - but using it fails. - it may be some incompatibility with something else.
The simplest solution for me is to do it without that library..

[fpistm]

Maybe linked a change on the HardwareTimer Library used by uTimerLib.
The main changes done was this PR: #2572
which harden and fix some issues.
So maybe uTimerLib required a small update but don't know which one.