Switch between VariSpeed modes disrupts UART1 communication



I’m using the Q2686H module with FW 6.63c and OS 4.23.02. I found a very strange effect of using the VariSpeed mode. In a function that needs a faster processing speed I set the VS mode to BOOST at the beginning and revert back to STANDARD at the function end. Before reverting back to NORMAL mode I send a response via UART1. This response becomes corrupted as the first characters (number of which varies) are garbage and only the last few are received correctly. If I move the switch to STANDARD mode before the call that sends the response then the UART1 works normally.

I presume that the baud rate generator is linked to the core speed and when this speed changes a time is needed for the clock (PLL?) to stabilize. During this time the baud rate is unstable with all the consequences.

Is anyone else experiencing such behavior? Is there any workaround known? Any other interface affected?

What are the consequences of running at BOOST speed all the time besides the higher power consumption? Higher EMC emissions or lower immunity, overheating at higher ambient temperatures or anything else? Because this is the only quick workaround for me in the short term.