Writing a kernel callout

If your hardware platform isn't supported by the kernel callouts in the startup library, or by any of the available board-specific kernel callouts, you will need to write your own callout.

If you need to write your own kernel callout, we recommend that you:

review your hardware documentation so that you understand what your kernel callout needs to do to complete its tasks successfully on your hardware
review and understand the kernel callout information in this chapter, and in particular the information about the type of callout you need to write (see “Kernel callout categories” in this chapter).
identify a kernel callout source file of the appropriate category that is close to the callout you need, then make a copy of it with a new filename, and modify the source code in this file (see “Kernel callout start and end macros” in this chapter).

Note:

The source file you start from should have C prototypes for the routines as comments, so you'll know what parameters are being passed in.

If the new routines you write will be useful on more than one board, you might want to keep the source file in your own private copy of the startup library. If the routines will be useful for your board only, you can just copy your file to the directory where you've put your other board-specific files.

For information about the locations and names of kernel callout source files, see “Kernel callout categories” in this chapter.