Hi there All, I have a problem which seemed to be defying explanation, but I have come up with a theory. Could I possibly have some feedback on whether the following is likely, plausible, possible, untrue or downright rubbish? If one reads the contents of a CAN or ADC chip register at a particular address, then the label volatile is placed upon that address to prevent the compiler optimising out repeat readings of the address. If one reads the contents of the address into a variable, then the compiler would automatically treat the contents of this variable with similar care. Is it possible that there has been an oversight with statements where the contents of a variable depend on the contents of a volatile by way of an if statement, ie...
normal_var=volatile_var;
normal_var=voltile_var; if (normal_var=0x00) { another_normal_var+=1; }
I'll second Mike's observation. There's absolutely no change at all between the three assembly outputs you show, as far as accesses to your CAN registers are concerned. They're those EXTB+MOVB pairs. Which means that whatever the real bug is, it's not in the piece of assembly code you did show. It's elsewhere. One thing I'm worried about is that I don't see any remains of the most significan byte actual addresses of your CAN registers (0x20) in any of the quoted code. Now, I don't do 166's at all, but this does feel fishy. Are you sure this code succeeds in accessing your CAN hardware registers at all, in the first place? You really should trace through this in some simulator or emulator to see what actually happens.
One thing I'm worried about is that I don't see any remains of the most significan byte actual addresses of your CAN registers (0x20) in any of the quoted code. It's those EXTP instructions. EXTP #080H,#01H is pretty much the same as EXTS #020H,#01H, which wouldn't alarm you. For some reason the C166 compiler prefers EXTP to EXTS, but that doesn't do any harm. - mike