>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>On Behalf Of Padu
>Sent: 12 November 2004 07:05
>To: Microcontroller discussion list - Public.
>Subject: [PIC]: Interrupt vs. Main loop
>
>
>I'm facing a conceptual dilemma, many of the gurus here and 
>elsewhere recommend to keep interrupt code to a minimum. 
>That's what I'm trying to do, but I'm having some serious 
>problems to transfer data gathered at the interrupt procedure 
>and use it on the main loop.
>
>The interrup is receiving a constant stream of UART data at 
>19200baud (it will be faster as soon as I get the appropriate 
>crystal). What I have to do is to interface with my 
>compactflash card and store each one of those bytes in it. I 
>intend to store data as FAT files (I know, 512 bytes blocks). 
>Thing is when I'm trying to process something on the main 
>loop, things are coming at a faster rate on the interrupt.
>
>One thing I've tried was to setup a circular list of 64 bytes, 
>push data on the interrupt and pop it on the main loop, it 
>didn't work. Then I've increased the circular buffer size to 
>128, then I started to see some of the expected bytes on my CF 
>(actually I'm sending them via USART to the PC just to test, 
>but I'll replace to writing to the CF later). When I increased 
>to 255, then almost got it, but still the interrupt was 
>winning the race. I feel that if I had a big enough buffer, 
>eventually it would work out, but perhaps there is a better 
>way to solve it.
>
>Should I put all my CF writing code in the interrupt 
>procedure? Would I be risking to get overrun errors?
>
>I have to confess, I'm enjoying learning all these new things 
>about PIC and electronics, but sometimes it's frustrating, 
>things don't happen at the same speed of software 
>development... or I'm too impatient to be a newbie again.

Does the main loop have to do a lot of other things at the same time as
writing to compact flash?  If yes, then you will simply have to arrange a
priority system, where the compact flash has the highest priority of all the
main loop tasks.

If writing data to the CF is all the main loop does then you have a simple
case of data coming in too quickly for the PIC to handle.  A larger buffer
will simply delay the problem if amount the data coming in is much larger
than the buffer size.  Some form of flow control on you serial link would be
the best solution.

Moving time consuming operations into the interrupt is simply going to
create you more problems, especialy if you up the bit rate as you will start
getting overrun problems.

Regards

Mike

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