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local variables lose values ?

Holger Warzelhan

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;

"done=0" was added to the list. Now, the compiled program seems to have a problem with the variable IsCancelled (set to 1 initially, but whenever referred to it in the function, it returns 0).

The .LST file shows this now (IsCancelled is not "working" anymore):

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

The old .LST file, when everything was still working, showed this:

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

Ok, the class of the variable in question has changed, but it should still work, shouldn't it?
What could cause the problem, and how would one prevent this from happening?

Any help would be great!

Thank you in advance.
Holger

Parents
  • 0 in reply to Mik Kleshov

    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;
    to make sure that it is placed in the memory area specified.
    Is there anything similar for the C166?

    Thank you, again!
    Holger

Reply
  • 0 in reply to Mik Kleshov

    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;
    to make sure that it is placed in the memory area specified.
    Is there anything similar for the C166?

    Thank you, again!
    Holger

Children
  • 0 in reply to Holger Warzelhan

    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.

  • 0 in reply to Mik Kleshov

    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

  • 0 in reply to Holger Warzelhan

    "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.