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Pointer to stack variables

I have a function that creates an instance of a structure on the users stack. The structure is called object and it is located at address 0xEFB0.

boolean CAN1_read(ubyte mbx, CAN_MSG *msg)
{
   ubyte     newd;
   TCAN1_Obj object;

   if ( newd = CAN1_ubNewData(mbx) )
   {
      CAN1_vGetMsgObj(mbx, &object);
      CAN1_vReleaseObj(mbx);
      msg->id   = object.ulArbitr;
      msg->size = object.ubMsgCfg >> 4;
      memcpy(&msg->data[0], &object.ubData[0], msg->size);
   }
   return((boolean)newd);
}

When the function CAN1_vGetMsgObject() is called, mbx is passed in R8 and the address of object is passed in R9 as 0x4FB0 Since DPP1 is zero, the address 0x0FB0 is being pointed to not 0xEFB0. DPP3 is three so 0xAFB0 would have worked.

I can "get around" this by casting to a huge pointer.

CAN1_vGetMsgObj(mbx, (TCAN1_Obj huge *)&object);

Or I suppose I could make object static but I would rather use temporary RAM space.

I can't help but think that the compiler should be smart enough to handle this and that I am doing something wrong. What do you guys think???

Thanks in advance,
-Walt

0 Mik Kleshov over 23 years ago
I had a similar problem with the following piece of code:

static const int OpCodes[][8]= { /* ... */ }; void SomeFunction(int n) { ( (void (*)(void)) (OpCodes[n]) ) (); }
When calculating the address for the function call the compiler took the wrong base address of the array (wrong DPP). When I changed Target->Near Memory->KB ROM setting, it started working. It left the impression that there was a serious bug in the compiler.

- Mike
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0 Walt Conley over 23 years ago in reply to Mik Kleshov

Interesting. This code seems so fundamental that I didn't even consider the possibility that it could be a bug. Does anyone have any ideas for things that I can try to make the code compile correctly without using a huge pointer?

-Walt
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0 Mik Kleshov over 23 years ago in reply to Walt Conley

Maybe switch to the previous version of the compiler?
- Mike
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0 Mik Kleshov over 23 years ago in reply to Walt Conley

Maybe switch to the previous version of the compiler?
- Mike
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0 Walt Conley over 23 years ago in reply to Mik Kleshov

Hi Mike:

The problems I describe in this thread and in a recent thread http://www.keil.com/forum/msgpage.asp?MsgID=4783 were both solved by turning off all compiler optimization. This was something that you suggested doing in the other thread but unfortunately I forgot about after being pulled from the project temporarily. After reviewing the other thread I decided to give it a try and was amazed that that was causing the problems I have been fighting for so long. Thanks again for your help.

-Walt
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