> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of solarwind
> Sent: 31 March 2009 20:56
> To: Microcontroller discussion list - Public.
> Subject: [PIC] Overloading interrupts...
> 
> What happens when interrupts are received faster than the time
> required for the ISR to complete?
> 
> For example, let's say I'm interrupting on UART receive, every time I
> receive a byte, so I can process it. However, the ISR may take a
> considerable amount of time to complete (hypothetical situation).
> Since there may be a possibility of receiving data really fast, the
> interrupt will be "hit" multiple times before the ISR has time to
> complete. What happens in this case? Does the ISR reset and go back to
> the beginning? Or does nothing happen until the ISR has completed?

Other have explained what would happen, but something to be aware of in
the case of the UART is that you will start losing data once the
hardware FIFO buffer is full.

The bottom line is that ISR's should in most cases be designed to run as
quickly as possible. In the case of a comms interrupt you would normally
just take the data out of the UART register and add it to a circular
buffer.  Your main program loop can than take data out of the buffer
when it needs to.

Regards

Mike

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