Hardware Interrupts
In this post we set up the programmable interrupt controller to correctly forward hardware interrupts to the CPU. To handle these interrupts we add new entries to our interrupt descriptor table, just like we did for our exception handlers. We will learn how to get periodic timer interrupts and how to get input from the keyboard.
This blog is openly developed on GitHub. If you have any problems or questions, please open an issue there. You can also leave comments at the bottom. The complete source code for this post can be found in the post-07 branch.
Table of Contents
🔗Overview
🔗Summary
This post explained how to enable and handle external interrupts. We learned about the 8259 PIC and its primary/secondary layout, the remapping of the interrupt numbers, and the "end of interrupt" signal. We implemented handlers for the hardware timer and the keyboard and learned about the hlt instruction, which halts the CPU until the next interrupt.
Now we are able to interact with our kernel and have some fundamental building blocks for creating a small shell or simple games.
🔗What's next?
Timer interrupts are essential for an operating system, because they provide a way to periodically interrupt the running process and regain control in the kernel. The kernel can then switch to a different process and create the illusion that multiple processes run in parallel.
But before we can create processes or threads, we need a way to allocate memory for them. The next posts will explore memory management to provide this fundamental building block.