[ECOS] Re: Uart missing chars when in Release

Grant Edwards grante@visi.com
Sun Jan 27 15:55:00 GMT 2008


On 2008-01-27, Laurie Gellatly <laurie.gellatly@netic.com> wrote:

>>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.

> With it set to 8 that should give 8 times as long to service
> the interrupt. 

Correct.  If you're using a 16 byte fifo, you should have up to
(16-threshold) byte times to respond to an interrupt.


>>Does it stop dropping bytes at lower baud rates?
>
> Try that next.

If the problem goes a way an lower baud rates, that would be an
important clue.

>>Does it stop dropping bytes if there is no Ethernet traffic?
>
> Tried that. No difference.

What other interrupt sources are active?  I wouldn't think the
timer tick would be an issue...

>>Running from flash is almost certainly slower, and I'd wager
>>that it increases the interrupt latency beyond what can be
>>tolerated by the serial interface's interrupt frequency.
>
> Maybe I should copy ISR or DSR to internal RAM or flash?

If it's a latency problem, you'd probably need to copy all ISRs
and DSRs to RAM (as well as any long-running functions called
by either of those).

>>> From what I've read, the OE gets cleared on each read of RBR.
>>> How can I check on this? Is there a counter of OE and other
>>> errors kept in eCos that I can access?
>
>>You've got the source code, you tell me.  -- I don't know what
>>low-level driver you're using. If it doesn't have an OE
>>counter, you can add one: it's only a couple lines of code.
>
> Counted the errors - none were shown.

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.)?

-- 
Grant Edwards                   grante             Yow!  Where's th' DAFFY
                                  at               DUCK EXHIBIT??
                               visi.com            


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