# API implementation overview

Implementing the API for a service includes:

- Creating the header files that contain the API function prototypes, error and event codes, and command code definitions.

- Writing the code that contains the API implementation.

- Declaring parameters in a parameter source (.pf) file.

Create the following files when implementing the service API:

File | Description
--- | ---
xxxapi.c | Implements the service API by calling the corresponding SPI function and handling API errors.
xxxdef.h | Contains API prototypes, event and error definitions, and public data structures.
xxxparm.pf | ASCII definition of each parameter and hierarchical structure.
xxxparm.c | Parameter source file automatically generated from xxxparm.pf.
xxxparm.h | Parameter header file automatically generated from xxxparm.pf.
xxxsys.h | Internal header file containing API command codes.