Features

Two example KISS kernels have been implemented. The K8 implementation only uses only interrupt disabling for mutual exclusion, and does not provide parameter checking or memory allocation, it was written only to demonstrate the basic kernel mechanisms. The K32 implementation provides parameter checking, resource tracking, memory management, priority inheritance and priority ceiling protocols, complex interrupt handling, and a device driver interface. It only lacks memory protection, a feature not found in the most popular realtime kernels anyway. While the K8 implementation is terminal, that is, no future development is expected except for minor bug fixes, the K32 implementation is a living creature.

All the features of the modern realtime kernels written in the last 10 years are present in KISS. The only omission at this time is memory protection. I simply did not have a suitable simulator or target on which to test an implementation.

If you wish to participate in the further development of this kernel, read the book The Design and Implementation of Realtime Kernels, as soon as it comes out. I am particularly interested in seeing memory protection, symmetric memory multiprocessing (SMP) and distributed processing implemented, in addition to the porting of the kernel to a variety of CPU architectures. I will probably port the kernel to the ARM processors myself.

Characteristics

The KISS kernel is scalable, in that only the portions of the kernel which are needed by the application are linked.

The kernel is realtime in that is it predictable and deterministic. The resource usage and timeliness of the kernel can be calculated given a known load.

The scheduler provides preemptive multitasking. The highest priority task is guaranteed to run within a deterministic amount of time of being readied. The scheduler also time-slices tasks of the same priority in a round-robin fashion, running any of the tasks for a fixed quantum of time.

Kernel calls are preemptable. A higher priority task can interrupt a lower priority task even when that task is executing a kernel call. Multitasking is prevented or interrupts are disabled only within the small critical sections that need it. The calls are also reentrant, more than one task can execute the same call at the same time.

The kernel provides resource tracking. Should an application terminate unexpectedly, all resources it had allocated are released.

There is full parameter checking. An application may not crash the system by giving the kernel invalid parameters.