"../6.user/DDcpu1.c", line 29: error #20: identifier "LED1_OFF" is undefined

The error message "identifier "LED1_OFF" is undefined" typically occurs when you are trying to use a function or variable (in this case, `LED1_OFF`) in the file `DDcpu1.c` that has not been declared or defined previously.

To resolve this issue, follow these steps[^1]:

1. **Check declaration**: Ensure that `LED1_OFF` has been declared as a function or macro somewhere else in your project. If it's a function, you might have forgotten to include the header file where it's defined, like:

   // In some_header_file.h
   void LED1_OFF();

2. **Include the proper header**: Make sure `DDcpu1.c` includes the correct header file containing the definition of `LED1_OFF`. Add the necessary `#include` directive at the beginning of the file if it's missing:

   // At the top of DDcpu1.c
   #include "some_header_file.h"

3. **Function definition**: If `LED1_OFF` is a function, ensure that its implementation is provided in the same compilation unit or another source file that gets linked together with `DDcpu1.c`.

4. **Macro check**: If `LED1_OFF` is a macro, make sure it's defined correctly. Macros usually start with `#define`:

   // In some_other_header_file.h
   #define LED1_OFF() /* Macro body */

After making these adjustments, recompile your code to see if the error is resolved.