Hi John I agree There is no waiting in my ISR. The only difference between my ISR and a standard one that just pushes every received char to a buffer is a test to see which buffer I push to. If it is a CMD char I push a byte to the command buffer if I have received a special character and I have set a flag I push the single char to a string buffer. If I receive a terminating char I push a CMD. If the string grows too long I know something has gone wrong and I clear the special char received flag and start over. So there are some tests but they are very short and only operate on a single character at a time and then move on. Either way I'm only pushing a byte and leaving there is no waiting for anything. Phillip Things should be as simple as possible but no simpler Phillip Coiner CTO, GPS Source, Inc. Your source for quality GNSS Networking Solutions and Design Services, Now! -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of John Chung Sent: Thursday, June 29, 2006 8:27 PM To: Microcontroller discussion list - Public. Subject: RE: [PIC] C18 calculating the interrupt loading --- Jan-Erik Soderholm wrote: > Phillip wrote : > > > ...if I get a special char I push the following > chars in > > a buffer to form strings... > > And that is done in the *following* interrupts, > right ? > > Or are you staying *in* the ISR waiting for those > "following chars" ? That is rather bad design, if > so. > > Generaly speaking, no ISR should ever *wait* for > anything. > > > I also agree that there is no real need to have a > priority > > scheme now but I don't see what it hurts. > > It adds complexity to the design, with is OK if you > need it... > > Fortunately this requirement is a rare occurance. If it locks itself in the ISR you can't get anywhere when the BOR occurs. Therefore it should be eliminated. John __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist