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110 lines
4.3 KiB
TeX
110 lines
4.3 KiB
TeX
\chapter{Device drivers}
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\section{Introduction}
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The purpose of a device driver is to act as an intermediate layer
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between an operating-specific API that is common for a group of
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similar devices and vendor-specific interfaces for individual types of
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devices.
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An important part of writing device drivers for a Lisp operating
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system is therefore to specify the different groups of devices and the
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corresponding operating-specific API for each group.%
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\footnote{As everything else in this document, this chapter is open to
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discussion. More so here, because I have no prior experience in
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defining device-driver APIs. -- RS}
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\section{Tickets}
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Some I/O operations, when called, return an object of type
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\emph{ticket}. A ticket is either \emph{pending} or it has
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\emph{expired}. A pending ticket corresponds to an I/O operation that
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is not yet complete.
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\Defprotoclass{ticket}
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The base class for all tickets.
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\Defclass{standard-ticket}
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Instantiable subclass of the class \texttt{ticket}
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\Defgeneric {expired-p} {ticket}
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Return true if and only if \textit{ticket} has expired.
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\Defun {wait-some} {\rest tickets}
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Suspend the current process until one of the tickets has expired.
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\Defun {wait-all} {\rest tickets}
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Suspend the current process until all of the tickets have expired.
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\section{Disk drivers}
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\Defprotoclass{disk}
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This is the root class of all disk device classes. A disk is a device
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that stores data in \emph{blocks}. The size of a block varies between
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different types of disks. Blocks are numbered from $0$ to $N-1$ where
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$N$ is the total number of blocks on this device. Because of the
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existence of bad blocks, $N$ may be smaller than the nominal size of
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the device. Nevertheless, the driver and the disk controller conspire
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to present the disk as contiguous sequence of blocks.
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\Defclass{standard-disk}
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This class is an instantiable subclass of the class \texttt{disk}.
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\Defgeneric {size} {disk}
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Return the number of blocks that \textit{disk} may store, so excluding
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bad blocks.
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\Defgeneric {block-size} {disk}
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Return the size of a native block for \textit{disk}. This size is the
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preferred size to use in transfers to and from this type of disk.
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\Defgeneric {write-block} {disk block address}
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Issue a \emph{write} operation transferring the data in \textit{block}
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to \textit{disk}. The parameter \textit{disk} is an
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instance of the class \textit{disk}, and \textit{block} is a a vector
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of type \texttt{(simple-array (unsigned-byte 8) (*))}. The size of
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\textit{block} must be a power of 2, and the address must be aligned
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to the size of \textit{block}. If the size of \textit{block} is
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\emph{smaller} than the native block size of \textit{disk} then a
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request to read an entire native block will be issued and the result
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will be stored in a temporary location. Part of the native block in
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the temporary location will then be overwritten by the contents of
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\textit{block}. Finally, the contents of the temporary location will
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be written to the device. If the size of \textit{block} is
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\emph{greater} than the native block size of \textit{disk}, then
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several native blocks will be written from \textit{block}.
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A call to this generic function returns an instance of the class
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\texttt{ticket}. The functions \texttt{wait-some} and
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\texttt{wait-all} can be used to wait for the I/O operation to finish.
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\Defgeneric {read-block} {disk block address}
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Read a block of data from the disk. The parameter \textit{disk} is an
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instance of the class \textit{disk}, and \textit{block} is a a vector
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of type \texttt{(simple-array (unsigned-byte 8) (*))}. The size of
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\textit{block} must be a power of 2, and the address must be aligned
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to the size of \textit{block}. If the size of \textit{block} is
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\emph{smaller} than the native block size of \textit{disk} then a
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request to read an entire native block will be issued and the result
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will be stored in a temporary location. Then a part of that native
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block will be copied to \textit{block}. If the size of \textit{block}
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is \emph{greater} than the native block size of \textit{disk}, then
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several native blocks will be read into \textit{block}.
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A call to this generic function returns an instance of the class
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\texttt{ticket}. The functions \texttt{wait-some} and
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\texttt{wait-all} can be used to wait for the I/O operation to finish.
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%% LocalWords: instantiable
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