Lpc2000

At 09:23 AM 1/20/05 +0000, you wrote:
>Is anyone aware of another way to start the transmit interrupt running on 
>the UART on an
>LPC2106 other than writing to the THR?

There isn't another way.

>I'd rather the interrupt routine take care of
>writing to the UART instead of another asynchronous thread of code doing 
>that.

Well, one way or another you've got to start the UART going.  I haven't run 
across a UART that doesn't need to be primed by writing to the transmit 
register.  (I trust you that they exist, I just don't remember running into 
one)

>  The hard part is when the software queue runs empty and
>the hardware queue runs empty the interrupt happens but does not persist 
>(this might be
>my libel assumption) and when the interrupt routine exits, the THR empty 
>status bit is still
>set but there is no more interrupt.

You need to set a flag when both queues have emptied so that the queuing 
routine can start up the UART again.

>Now if the software queue is loaded up, to get the
>interrupt to trigger the queue transfer to the hardware queue, I have to 
>transfer one value
>to trigger the interrupt to do the rest.  In other tx interrupt on other 
>micros the interrupt
>persists and you just flip a control register bit and turn it off to block 
>the interrupt until
>the software queue is loaded again whereupon you set the bit back on.

I don't see this as substantively different.  In one case you write to the 
transmit register, in the other the interrupt enable register, but in both 
cases you need to set a flag when both queues are empty and respond 
accordingly.

For the 16550 style case the routines look something like

transmit ()
{

if( SW queue is empty) {
    empty_flag = 1;
    }
else {
    stuff the 16550 HW queue appropriately
    }

}


interrupt_transmit_routine()
{
transmit()
}

queueing_routine( void *ptr, size_t len)
{

Add  incoming data to queue

when all data added (or queue filled) {
    if( empty_flag != 0) {
          disable interrupts
          transmit()
          restore interrupts
          }
    }
}

The only difference from the peripheral interrupt enable/disable approach 
is the use of the transmit call in the queuing routine rather than a set 
interrupt on call (or line).  All the rest of the code is necessary anyway.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III