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From: Charles Sandmann <sandmann AT clio DOT rice DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: optimization.bug
Date: Thu, 17 Aug 1995 07:43:35 CDT
Organization: Rice University, Houston, Texas
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> With any of the optimizations selected, the 2nd while loop never terminates
> as the busy bit always appears high.  With no optimization the code works
> as expected.

Try to do a gcc -O2 -S on your code, then look at the GAS code generated.
It is possible that the inlined port functions don't have enough of a 
"wait" between operations on that port, or GCC has optimized something
away it should not have.  If the assembly looks correct on the second
loop which hangs, you can try to add some jmp 1f; 1: type statements
to see if delays help.  Step through it with the debugger.