How to design and implement simple interface ?

// Some_Filename.c  -  This file already exists
 /* This function fetches two bytes from Non-Volatile Memory(NVM) and
returns to the calling library. */

 signed short GetDeltaMin ( void )  
  {
       signed short param;
       NVM_Read ( ( unsigned char * ) &param );
       return (signed short) param;
  }

 // New File -  Activate_Deactive_I.c

  void Enable_Disable ( Boolean State)
  {
       /* user will pass 1 or 0 to this function. */
      /* If State =1, there is no change to GetDeltaMin ( ).  It'll still
pass two byte value from NVRAM to the calling library  */
     /* If State = 0, GetDeltaMin ( ) needs to pass 0 to calling library
instead of two byte value from
          from NVRAM. */
     /* Please write this function and modify GetDeltaMin ( ).  */
  }

 New File -  Activate_Deactivate.h
  extern void Enable_Disable ( Boolean State);   /* This header file must
be included in file from where Enable_Disable (  ) will be called.  */
  /* I don't think Activate_Deactive_I.c needs to include this header file
?   */ 
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Am 19.07.2015 um 20:32 schrieb learn:

[an obvious homework task]

That's _your_ homework, so _you_ do it.  Who knows, you might even
change "learn" from your silly moniker to something you actually did.

>Am 19.07.2015 um 20:32 schrieb learn:
>
>[an obvious homework task]
>
>That's _your_ homework, so _you_ do it.  Who knows, you might even
>change "learn" from your silly moniker to something you actually did.


I am not in school.  I know how to do this with a global variable.  When
Enable_Disable( ) is called, I can set a global variable to 1 or 0.  Then,
in GetDeltaMin( ) I can use the value of the global variable to decide
whether to send NVM value or 0 to calling library.

The reason I am asking this question is because I'm looking for better
solution than a global variable.
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On 7/19/15 4:46 PM, learn wrote:
>> Am 19.07.2015 um 20:32 schrieb learn:
>>
>> [an obvious homework task]
>>
>> That's _your_ homework, so _you_ do it.  Who knows, you might even
>> change "learn" from your silly moniker to something you actually did.
>
>
> I am not in school.  I know how to do this with a global variable.  When
> Enable_Disable( ) is called, I can set a global variable to 1 or 0.  Then,
> in GetDeltaMin( ) I can use the value of the global variable to decide
> whether to send NVM value or 0 to calling library.
>
> The reason I am asking this question is because I'm looking for better
> solution than a global variable.

Other options would be a file scope variable, and either putting the function into the file of the original function, or adding a call to a function to get the value of the variable.

In Enable_Disable returns the previous value, then it could be used to get the value (and called again to set it back if needed) and then the flag could be stored in a function static variable.

>On 7/19/15 4:46 PM, learn wrote:
>>> Am 19.07.2015 um 20:32 schrieb learn:
>>>
>>> [an obvious homework task]
>>>
>>> That's _your_ homework, so _you_ do it.  Who knows, you might even
>>> change "learn" from your silly moniker to something you actually did.
>>
>>
>> I am not in school.  I know how to do this with a global variable. 
When
>> Enable_Disable( ) is called, I can set a global variable to 1 or 0. 
>Then,
>> in GetDeltaMin( ) I can use the value of the global variable to decide
>> whether to send NVM value or 0 to calling library.
>>
>> The reason I am asking this question is because I'm looking for better
>> solution than a global variable.
>
>Other options would be a file scope variable, and either putting the
>function into the file of the original function, or adding a call to a
>function to get the value of the variable.
>
>In Enable_Disable returns the previous value, then it could be used to
get
>the value (and called again to set it back if needed) and then the flag
>could be stored in a function static variable.



I would like to add a call to a function to get the value of the variable.
 This means GetDeltaMin( ) will call Enable_Disable( ) at a fast rate,
maybe every 1.25ms to fetch the value. 
And some other function will call Enable_Disable( ) infrequently to pass
value of 0 or 1.
We have non-preemptive Operating System.  Will there be any mutually
Exclusion problem with calling Enable_Disable( ) from Two places ?
---------------------------------------
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>>On 7/19/15 4:46 PM, learn wrote:
>>>> Am 19.07.2015 um 20:32 schrieb learn:
>>>>
>>>> [an obvious homework task]
>>>>
>>>> That's _your_ homework, so _you_ do it.  Who knows, you might even
>>>> change "learn" from your silly moniker to something you actually
did.
>>>
>>>
>>> I am not in school.  I know how to do this with a global variable. 
>When
>>> Enable_Disable( ) is called, I can set a global variable to 1 or 0. 
>>Then,
>>> in GetDeltaMin( ) I can use the value of the global variable to
decide
>>> whether to send NVM value or 0 to calling library.
>>>
>>> The reason I am asking this question is because I'm looking for
better
>>> solution than a global variable.
>>
>>Other options would be a file scope variable, and either putting the
>>function into the file of the original function, or adding a call to a
>>function to get the value of the variable.
>>
>>In Enable_Disable returns the previous value, then it could be used to
>get
>>the value (and called again to set it back if needed) and then the flag
>>could be stored in a function static variable.
>
>
>
>I would like to add a call to a function to get the value of the
variable.
> This means GetDeltaMin( ) will call Enable_Disable( ) at a fast rate,
>maybe every 1.25ms to fetch the value. 
>And some other function will call Enable_Disable( ) infrequently to pass
>value of 0 or 1.
>We have non-preemptive Operating System.  Will there be any mutually
>Exclusion problem with calling Enable_Disable( ) from Two places ?
>---------------------------------------
>Posted through http://www.EmbeddedRelated.com


Thank you for the solution and replies.
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