Le lundi 19 octobre 2009, prateek sikka a écrit :
> We are facing an issue with serial port reception code we have written.
> All the local variables are overwritten by the third value read from the
> serial port.
> [...]
> Can someone comment on it?
I've noticed some strange quirks with some code I'm writing as well (but being
a newcomer in C, I always wonder if the quirks come from the compiler or are
located between the keyboard and chair...) However I saw a very puzzling
example last night in a thing that took me hours debugging - target is a
PIC16F886. Example code :
// PIC output register
#define O_BUZ RB3
// All the following are global variables defined in another.c file
volatile octetBits flag;
unsigned short int tuneRepeat;
unsigned short int tuneAddr;
unsigned short int tunePos;
// 2 following functions are in the main .c file
// Function that stops playing a tune
void subStopTune() {
TMR2IE=0;
TMR2ON=0;
TMR2IF=0;
O_BUZ=0;
flag.tunePlaying=0;
tuneRepeat=0; tuneAddr=0; tunePos=0;
}
// Function that starts playing a tune
void subPlayTune(unsigned short int address, unsigned short int repeat) {
subStopTune(); // Stops previously playing tune, if any
tuneRepeat=repeat;
if (tuneRepeat>0) tuneRepeat--; // 0=1 ;-)
tuneAddr=address;
tunePos=address;
flag.tunePlaying=1;
subContTune(); // Play it
}
That looks simple enough, but what I had is that the tunes were properly
playing, but never repeating. Debugging showed me that the "tuneRepeat"
variable was always 0 when exiting subPlayTune(), whatever value could have
the "repeat" parameter used when calling it :-(
After hours of debugging I found out that tuneRepeat was zero because it was
zeroed in subStopTune(), even though subPlayTune() was setting it _after_
coming back from subStopTune() !
The tunePos and tuneAddr variables that seemed to be reset and set exactly the
same way were however working properly !
Just removing "tuneRepeat=0;" from subStopTune() solved my problem, but for no
reason that I'm able to understand - except for #me being stupid or a compiler
quirk...
--
Michel Bouissou (OpenPGP ID 0xEB04D09C)
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