51 Setting variables, arrays, and functions in fixed positions in single-chip microcomputers

1. Variables or arrays without initial values

Simply use the _at_ keyword plus the address.

like:

 unsigned char idata myvar _at_ 0x40;

 unsigned char code myvar[10] _at_ 0x40;

There are spaces before and after the _at_ keyword.

2. Variables or arrays with initial values

To locate a variable at an absolute position and assign an initial value, you cannot use _at_ to complete the task. You need to do the following:

1. Create a new file in the project, such as InitVars.c, and assign initial values ​​to the variables to be processed (assuming it is code variables):

char code myVer = {"COPYRIGHT 2001-11"};

2. Then add the file to the project, compile, open the M51 file, if the definition is code type, then

* * *   C O D E   M E M O R Y   * * *

You can find below:

CODE    xxxxH     xxxxH     UNIT         ?CO?INITVARS

Then in:

Project->Options for Target ...->BL51 Locate：Code

Fill in:

?CO?INITVARS(0x200)

Just compile again.

1. Correspondingly, if it is an xdata variable, write in InitVars.c:

char xdata myVer = {"COPYRIGHT 2001-11"};

Then add the file to the project, compile, open the M51 file, and

* * *  X D A T A   M E M O R Y  * * *

You can find below:

XDATA   xxxxH     xxxxH     UNIT         ?XD?INITVARS

Then in:

Project->Options for Target ...->BL51 Locate：Xdata

Fill in:

?XD?INITVARS(0x200)

Compile again. Correspondingly, if the variables such as data/idata are defined, just handle them accordingly.

3. Function Positioning

If you want to C source file tools.c function

int BIN2HEX(int xx)

{

  ...

}

Place it at 0x1000 of CODE MEMORY, compile the project first, then open the M51 file of the project,

* * *   C O D E   M E M O R Y   * * *

Find the name of the function to be located under the line, which should be like:

CODE    xxxxH     xxxxH     UNIT         ?PR?_BCD2HEX?TOOLS

Then in:

Project->Options for Target ...->BL51 Locate：Code

Fill in the following information:

?PR?_BCD2HEX?TOOLS(0x1000)

Build again, and you will find that the function has been placed at 0x1000 in CODE MEMORY in M51.

If you want to locate multiple functions at the same time, just separate them with ",":

   ?PR?myTest1?MAIN(0x3900), ?PR?myTest2?MAIN(0x4000)

4. Calling method when you know the function address but not the function name (using function pointer to call the function at the absolute address)

1. Define the prototype of the function to be called

typedef void (*CALL_MYTEST)(void);

This is a prototype of a callback function, the parameter is empty.

2. Define the corresponding function pointer variable

CALL_MYTEST    myTestCall = NULL;

3. Function pointer variable assignment, pointing to the function at the absolute address we locate

myTestCall = 0x3900;

4. Function pointer call

                     if (myTestCall != NULL)

                     {

                            myTestCall(); // Call the function myTest1 at the function pointer, set the PC pointer to 0x3900

                     }