When implementing a device driver, a developer has to resolve two main problems:
- How to exchange data with peripherals
- How to manage interrupts that peripherals generate to the CPU
The first point was covered (at least for char drivers) in previous chapters, while the second one (and its related matter) will be the main topic of this chapter.
In the kernel, we can consider the CPU (or the internal core executing some code) running in two main execution contexts — the interrupt context and the process context. The interrupt context is very easy to understand; in fact, the CPU is in this context each time it executes an interrupt handler (that is, special code the kernel executes each time an interrupt occurs). In addition to this, interrupts can be generated by the hardware or even by the software; that's why we talk about hardware...
