Hi sel4 development team,

I understand from the seL4 kernel the initial printf message are not routed through sel4 platform uart driver. Because the sel4 UART driver initialisation happened later when seL4 Main kernel initialization is finished.

till then sel4 kernel uses u-boot UART driver to route the message.

This interpretation is correct as per my understanding.

Also mentioned in code as well debug output available via serial interface after kernel init thread started.

  /* debug output via serial port is only available from here */
    printf("Bootstrapping kernel\n");

It means that when sel4 kernel comes up with u-boot uart driver and then later using sel4 uart driver.
 
Please correct me if any thing wrong here and throw some input.