THE KERNAL

One of the problems facing programmers in the microcomputer field is the question of what to do when changes are made to the operating system of the computer by the company. Machine language programs which took much time to develop might no longer work, forcing major revisions in the program. To alleviate this problem, Commodore has developed a method of protecting software writers called the KERNAL.

Essentially, the KERNAL is a standardized JUMP TABLE to the input, output, and memory management routines in the operating system. The locations of each routine in ROM may change as the system is upgraded. But the KERNAL jump table will always be changed to match. If your machine language routines only use the system ROM routines through the KERNAL, it will take much less work to modify them, should that need ever arise.

The KERNAL is the operating system of the Commodore 64 computer. All input, output, and memory management is controlled by the KERNAL.

To simplify the machine language programs you write, and to make sure that future versions of the Commodore 64 operating system don't make your machine language programs obsolete, the KERNAL contains a jump table for you to use. By taking advantage of the 39 input/output routines and other utilities available to you from the table, not only do you save time, you also make it easier to translate your programs from one Commodore computer to another.

The jump table is located on the last page of memory, in read-only memory (ROM).

To use the KERNAL jump table, first you set up the parameters that the KERNAL routine needs to work. Then JSR (Jump to SubRoutine) to the proper place in the KERNAL jump table. After performing its function, the KERNAL transfers control back to your machine language program. Depending on which KERNAL routine you are using, certain registers may pass parameters back to your program. The particular registers for each KERNAL routine may be found in the individual descriptions of the KERNAL subroutines.