[ECOS] Re: Uart missing chars when in Release

Grant Edwards grante@visi.com
Mon Jan 28 02:37:00 GMT 2008


On 2008-01-28, Laurie Gellatly <laurie.gellatly@netic.com> wrote:
> Hi Grant,
>> >>At 117Kbps with no fifo, you have to service a receive
>> >>interrupt at a 11.7KHz or you lose bytes.  That means you've
>> >>got to have an interrupt latency less than 85us.
>> >
>> > So I modified ser_16X5X.c to read FIFO threshold (1,4,8 or 14)
>> > characters worth when an RDA interrupt occurs.
>> 
>> What was it doing?  The correct thing to do is to read all the
>> available characters each time an rx interrupt occurs.
>
> In the switch statement the (RDA)ISR_Rx case simply fell through 
> to the (CTI) ISR_RxTO case and a single character was read from RHR.

That's wrong.  It should continue to read bytes from RHR as
long as the status register says there is receive data
available.  What you describe isn't what's in my snapthost
snapshot of ser_16x5x.c.  The code I'm looking at is right: in
the Rx/RxTO case, there's a loop that reads all of the data
from the receive fifo.  My snapshot is proably a couple years
old, and it's doing the right thing.  Where did you get the
broken file?

>> If there aren't any receive overrun errors, then interrupt
>> latency isn't the problem.  There weren't any rx errors of any
>> sort (parity, framing, etc.)?
>
> Yeah, I thought this was strange as well. After I slept on it
> I found that the Rx Line Status Interrupt was not enabled.... 
> Now I see I'm getting OE.

It sounds like you've somehow gotten ahold of a broken serial
driver code.  I checked CVS, and it's got the right code in it.
I've checked all the versions back for 4 years, and they all
have a loop that will read all available rx data whenever
there's an interrupt.  Are you sure you have driver code that
only reads a single byte?

You shouldn't have had to do anything other than enble the
fifo.  The code that's in CVS is correct.

-- 
Grant




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