RE: [ECOS] Re: Uart missing chars when in Release

["Laurie Gellatly" <laurie dot gellatly at netic dot com>]

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.

> > 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.
I'm using 8 at present so I have an additional 8 char times (to make
16 in the FIFO) to service the first 8.
> 
> >>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.
Its using the generic serial driver from devs/serial/generic/16x5x
> > 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.)?

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.

		...Laurie:{)



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