SMART CAR\SMART CAR.axf: Error: L6218E: Undefined symbol _HAL_TIM_SET_COMPARE (referred from pwm.o).

The error message is indicating that there is an undefined symbol "_HAL_TIM_SET_COMPARE" in the "pwm.o" file, which is preventing the linker from linking the object file to the final executable file.

This error typically occurs when the linker cannot find the definition of a function or variable that is referenced in the code. In this case, it seems that the function "_HAL_TIM_SET_COMPARE" is either missing or not properly defined in the code.

To fix this error, you need to ensure that the function definition for "_HAL_TIM_SET_COMPARE" is included in your code or library. You may also need to check if there are any missing include files, or if the correct library is being linked.

You should also check if the function name is spelled correctly, as any typos or errors in the function name can cause this error. Once you have resolved the issue, try recompiling and linking your code to see if the error has been resolved.