I'm running V5.0.2 on an Atmel AT3UCA0512. The UART ISR handles both transmitter empty and receiver full interrupts by either pulling a character from a queue or posting a character to a queue. If both conditions are simultaneously true then the ISR could potentially activate TWO tasks.

Is this possible, or illegal, or what? How would I handle this? Would I detect that the 1st task has been activated and ignore the 2nd interrupt cause, leaving the IRQ to fire again and then handling the 2nd interrupt source? Or do I just note that a task was activated and let taskYIELD_FROM_ISR() figure it out?

No problem.

void interrupt_routine( void )
{
int Woken = 0;

// Do something.

// Send to a task. Woken will be set
// to true if this send wakes a task.
xQueueSendFromISR(q, &Woken);

// Do something else.

// Send to another task. Again, Woken
// will be set to true if this send
// wakes a task.
xQueueSendFromISR(q2, &Woken);

// Two sends so you might have woken
// two tasks. FreeRTOS will have done
// this for you, but will always return
// to the highest priority ready task
// which might be one of the two tasks
// woken in this isr, or might be the
// task that was originally running
// anyway.
portYIELD_FROM_ISR(Woken);
}

Great, thanks !!!