christoph/interrupt-handling-using-the-x86-apic
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Christoph Urlacher
2023-03-03 15:40:25 +01:00
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chap/background.tex
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\chapter{Background}
\label{ch:background}
In this section, important domain-specific concepts will be explained, to create the necessary foundation to follow \autoref{ch:implementation}.
In this chapter, important domain-specific concepts will be explained, to create the necessary foundation to follow \autoref{ch:implementation}.
Important terms present in the glossary are marked in \textbf{bold} on their first occurrence.
\clearpage
@ -347,25 +347,4 @@ PC/AT compatibility is usually achieved in these systems by connecting two PICs
Specifics on handling PC/AT compatible external interrupts follow in \autoref{subsec:ioapicpcat}.
\section{Interrupt Handling in HhuOS}
\label{sec:currenthhuos}
In hhuOS, external interrupts are handled in two stages (see \autoref{subsec:apxcurrenthhuos} for code examples):
\begin{enumerate}
\item After an IRQ is sent by an interrupt controller, the CPU looks up the interrupt handler address in the IDT\@.
In hhuOS, every IDT entry contains the address of the \code{dispatch} function, which is invoked with the vector number of the interrupt.
\item The \code{dispatch} function determines which interrupt handler will be called, based on the supplied vector number.
In hhuOS, interrupt handlers are implemented through the \code{InterruptHandler} interface, that provides the \code{trigger} function, which contains the interrupt handling routine.
To allow the \code{dispatch} function to find the desired interrupt handler, it has to be registered to a vector number by the OS beforehand.
This process is handled by the \code{plugin} function of the interrupt handler interface, which uses the interrupt dispatcher's \code{assign} function to register itself to the correct vector number.
HhuOS supports assigning multiple interrupt handlers to a single interrupt vector and cascading interrupts.
\end{enumerate}
To prevent the need of interacting with a specific interrupt controller implementation (e.g. \code{Pic} class) or the dispatcher, a system service (the \code{InterruptService}) is implemented to expose this functionality to other parts of the OS (it allows e.g.\ registering interrupt handlers or masking and unmasking interrupts).
Currently, hhuOS utilizes the PIT to manage the global system time, which in turn is used to trigger hhuOS' preemptive round-robin scheduler (the \code{Scheduler} class).
The PIT and other devices are initialized before the system entry point, in the \code{System::initializeSystem} function.
\cleardoublepage