Hi, is it recommended to start an usart_isr before the vTaskStartScheduler() will be started? Are there any kind of drawbacks? Which configuration would you suggest (using a semaphore or global variable within the isr)? best regards
Bernd

Normally interrupts will be disabled before the scheduler is started. If you do use interrupts before the scheduler is started then you must ensure that no interrupt service routines try and perform a context switch, as to do so before the scheduler was initialized would cause a crash.

Do you know a recommended way to enable the interrupts after starting the scheduler? If the usage of a global variable is perfect, where do I have to set this variable (to enable the interrupts)? Or is it possible using the variable  xSchedulerRunning = pdTRUE;
-> if true is correct, interrupts are enabled.

Interrupts will be enabled automatically when the first task starts running (assuming the FreeRTOS code is unchanged) so you don’t need to do anything from the application code. If you want the interrupt handler to only execute when the scheduler is running then testing xSchedulerRunning is a good method, but be careful as some ports require the task context to be saved before any C code executes, so before you can test the xSchedulerRunning value.