Lpc2000

--- In lpc2000@yahoogroups.com, "Dave" <dgsomerton@w...> wrote:
> --- In lpc2000@yahoogroups.com, "vajper0" <ph@w...> wrote:
> > I'm writing a driver for UART1 on a LPC2138. So far most things 
seems
> > to work (considering the crappy hardware capabilities). My current
> > problem is that I loose interrupts when receiving data.
> > 
> > I run the UART in 115200bps and my ISR takes care of all IRQs 
except
> > the modem status ones that are not enabled. If I send a block of a
> > couple of hundreds characters, sometimes one RDA IRQ is lost. I 
know
> > this because the missing data always are the size of the Rx 
trigger
> level.
> > 
> > The ISR reads the U1IIR once in the beginning, compares the 
register
> > data to the different IRQ types in priority order. The first 
matching
> > type is handled (and the IRQ resetted), the U1IIR is then read 
again
> > and so on. When no more pending IRQs, the ISR is exited. When a 
> > 
> > Am I missing something essential?
> 
> Hello,
> 
>   I use a 2132, but the initial development was done on a 2138
> evaluation board from keil, the M something 2130.
>   I have interrupt comm at 115200, and do not seem to miss any.
>   Do you enable the FIFO? If so, do you empty the FIFO each RX data
> IRQ? If so, do you also enable the TIMEOUT IRQ and collect the
> remainder data (less than one FIFO).
>   In my application, I set the FIFO to 14 bytes (the maximum).
>   In the IRQ I loop until the IIR reads no pending.
>   As this application also uses rs485 half duplex, I thought the 
TEMPT
>  (transmitter empty) bit could generate an interrupt, and the
> direction could be dropped changed back to listen. But it does not, 
so
> on tx complete, a flag is set, and the timer IRQ looks for the TEMPT
> bit and does it's thing.
>   A similar thing to detect when the line is available, each RX IRQ,
> set the 'receiving' flag, and mark the time of the reception. 
When 'a
> certain amount of time has passed without receiving characters' 
could
> be a clear channel.
>   A slight modification of this was, when the TIMEOUT interrupt
> occurs, this indicates clear channel of at least '3.5' character
> times, and this can be used. Well infact it is used, but the other
> method also remains, as what if the last block of received data is
> exactly one FIFO long, then no TIMEOUT IRQ will come, and so the 
timer
> method of clear channel detection is used. This is controlled by a
> single flag and a time of last reception value.
> 
>   Anything else?
>   Being at home now, the code is not available, but I could send
> something tomorrow when I get to work. But really, it's not that
> difficult.
> 
> Dave

Firstly I figured out one of my issues.  I was trying to setup a HDLC-
ish style link since I need to send packets of data.  I was using the 
7E for the flag and idle in the link as specified.  Figured out if 
you send a constant stream of these its very easy for the UART to mis-
interpret the start bit and receive F9 characters instead of 7E.  I 
changed the flag character and this changed some of my issues but not 
all.

With that said I still have all the other issues related to 
interrupts and errors.  What I do is check the U1IIR and then go to 
the proper subroutine depending on what interrupt it specifies.  In 
the transmit routine I send out the buffered data or idle characters 
till the TX FIFO is full.  In the receive routine I read all the 
characters till the RDA bit goes low in the U1LSR register therefor 
emptying the RX FIFO.  I suspect I do not use the character timeout 
much since I am sending idle characters to ensure the link is always 
active so I can tell if the link is broken as soon as it occurs.  
Once these subroutines are done I go back to the main interrupt 
service routine and check to see if another serial interrupt is 
pending and process it also.

I also check for errors in U1LSR as I am reading data and am clearing 
them by reading and discarding the data.  I also was flushing the RX 
FIFO but commented that part out for the moment incase that was the 
cause of some of my issues.

Any info you can give me would be great.  Thank you.

Pascal