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Hello, I have a project (C166/HUGE memory model), where some local variables seems to lose their values. Everything worked fine, until I added some more code to a specific function (and one more local variable):
unsigned char Ptmp=0,FSzu=0,IsCancelled=1,errors=0, FSDin,f3=0,f4=0,Abort=0,ii,done=0;
NAME CLASS SPACE TYPE OFFSET SIZE ---------------------------------------------------- Ptmp . . . . --reg-- uchar ----- 1 FSzu . . . . auto uchar 2H 1 IsCancelled. auto uchar 0H 1 errors . . . auto uchar 6H 1 FSDin. . . . auto uchar 8H 1 f3 . . . . . auto uchar AH 1 f4 . . . . . auto uchar CH 1 Abort. . . . auto uchar EH 1 ii . . . . . --reg-- uchar ----- 1 done . . . . auto uchar 2H 1
NAME CLASS SPACE TYPE OFFSET SIZE ---------------------------------------------------- Ptmp . . . . auto uchar 0H 1 FSzu . . . . auto uchar 2H 1 IsCancelled. --reg-- uchar ----- 1 errors . . . auto uchar 6H 1 FSDin. . . . auto uchar 8H 1 f3 . . . . . auto uchar AH 1 f4 . . . . . auto uchar CH 1 Abort. . . . auto uchar EH 1 ii . . . . . --reg-- uchar ----- 1
Hello again, I forgot to mention that I am using version 3.12 of the C166 package. Playing around with some options in MicroVision, I found that it seems to work fine again after using "Use static memory for non-register automatics" in the compiler options. This gives me an .LST file showing:
NAME CLASS SPACE TYPE OFFSET SIZE ---------------------------- Ptmp . . . . auto NDATA uchar 0H 1 FSzu . . . . auto FCODE uchar 2H 1 IsCancelled. auto NDATA uchar 2H 1 errors . . . auto FCODE uchar 6H 1 FSDin. . . . auto FCODE uchar 8H 1 f3 . . . . . auto FCODE uchar AH 1 f4 . . . . . auto FCODE uchar CH 1 Abort. . . . auto FCODE uchar EH 1 ii . . . . . auto NDATA uchar 4H 1 done . . . . auto NDATA uchar 6H 1
Local variables must not loose their values, no doubt about that. In order to see what's happening exactly you have to look through the generated code listing and maybe single-step through the code in the simulator. The problem is, with so many local variables it will be hard to keep track of them all. The "Use static memory for non-register automatics" option in essence adds the "static" storage class modifier to every non-register local variable. The problem is, it can make all your functions non-reentrant. To avoid that, you can declare only some of your local variables as "static". Hopefully, it will help you avoid the problem of local variables loosing their values and you will still be able to decide which function must be reentrant and which one doesn't have to be. And the last but not the least: with such coding style (lots of automatic variables) you can easily run out of stack space, which can cause all sorts of problems. Check that you have enough stack memory allocated for user stack. Regards, Mike
How can I prevent "auto" variables? The handbook talks a lot about how they are handled and placed, but as far as I see there is no way to directly place a variable in a specific place. Coming from C51, there was always an easy way to declare a variable as
unsigned char xdata varname;
The static keyword is designed for that. By default, local variables have the auto storage class pecifier. You can find details in K&R, for example.
Hello! what would be a reason against making "everything static" with the compiler option? Functions wouldn't be reentrant anymore, but if you don't have any functions that have to be, is there any reason why not to do this? ISRs should also run if they're static, since a new interrupt during the execution of the previous one would just wait until the previous one is handled. Thanks for any advice! Holger
"what would be a reason against making "everything static" with the compiler option?" That'd mean you'd need to allocate RAM for every single local variable. "Conventional" 'C' compilers allocate local variables on the Stack, so you only need enough RAM for the maximum number of local variables in use simultaneously C51 uses a data overlaying technique to achieve a similar end. I dunno how C166 does it.