docs/x86/PIC.tex

   1 \documentclass[a4paper,10pt]{article}
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   3 \renewcommand*{\tablename}{\small\textbf{Table}}
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   5 \renewcommand*{\abstractname}{\small\textbf{Abstract}}
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   7 \begin{document}
   8
   9 \title{\textbf{Programmable Interrupt Controller}}
  10 \author{Pawel Dziepak}
  11 \date{\textit{January 09, 2009}}
  12 \maketitle
  13
  14 \section{Role of the PIC}
  15 \paragraph{}The main PIC task is to control all interrupts requests (IRQs) reported by
  16 the hardware. In most computers there are two PIC microcontrollers, each control
  17 eight IRQs. When a device reports IRQ, dependently on the PIC configuration
  18 a CPU interrupt is performed, which allow the device driver to do all needed
  19 things to keep device working.
  20
  21 \section{PIC configuration (ICW)}
  22
  23 \begin{table}
  24 \begin{tabular}{ll}
  25 \textbf{bit} & \textbf{meaning} \\
  26 0 & if set, ICW4 will be sent \\
  27 1 & if set there is only one PIC, zero means that there are two PICs \\
  28 2 & always zeroed \\
  29 3 & method of reporting IRQs \\
  30 4-7 & signature of the command (0001b)
  31 \end{tabular}
  32 \caption{ICW1}
  33 \label{icw1}
  34 \end{table}
  35
  36 \begin{table}
  37 \begin{tabular}{ll}
  38 \textbf{bit} & \textbf{meaning} \\
  39 0-2 & always zeroed \\
  40 3-7 & offset of the interrupt vector (in translation IRQ-interrupt)
  41 \end{tabular}
  42 \caption{ICW2}
  43 \end{table}
  44
  45 \begin{table}
  46 \begin{tabular}{ll}
  47 \textbf{bit} & \textbf{meaning} \\
  48 0-7 & if bit on a specific position is set it means that it is \\
  49     & the place of the connection with slave PIC
  50 \end{tabular}
  51 \caption{ICW3 (master)}
  52 \end{table}
  53
  54 \begin{table}
  55 \begin{tabular}{ll}
  56 \textbf{bit} & \textbf{meaning} \\
  57 0-2 & slave PIC's ID, not really used in standard PCs \\
  58 3-7 & always zeroed
  59 \end{tabular}
  60 \caption{ICW3 (slave)}
  61 \end{table}
  62
  63 \begin{table}
  64 \begin{tabular}{ll}
  65 \textbf{bit} & \textbf{meaning} \\
  66 0 & if set 8-bit interrupts vector will be used, if zeroed 16-bit \\
  67   & addressing will be used \\
  68 1 & if set mode AEOI will be enabled what means that EOI message \\
  69   & will be sent automatically \\
  70 2 & used to specify which controller is the command addressed to, \\
  71   & \textbf{only} when bit 3 is set \\
  72 3 & if set buffered mode will be enabled, not used on standard PCs \\
  73 4 & if set modifies method of transmission master-slave, not used \\
  74   &on standard PCs \\
  75 7-5 & always zeroed \\
  76 \end{tabular}
  77 \caption{ICW4}
  78 \label{icw4}
  79 \end{table}
  80
  81 \paragraph{}PIC is once configured during system start. Then small changes in configuration
  82 are performed only while loading or destroying device drivers (look at point 3,
  83 Disabling/enabling IRQs).
  84 \paragraph{}When PIC is initialized, correct connections CPU interrupt - IRQ are set. It is
  85 done by sending ICWs (initialization command word). The first ICW is sent to the port \texttt{0x20} if
  86 it is destinated for master or \texttt{0xA0} if for slave. The other ICWs are sent to the ports
  87 \texttt{0x21} for master and \texttt{0xA1} for slave. ICW3 is sent only when there are two PICs in
  88 the system. The command is different for master and for slave microcontroller. ICW4 is sent
  89 only if first bit (bit 0) of ICW1 is set. Tables \ref{icw1} to \ref{icw4} presents the structure of each
  90 ICW. After receiving all 4 commands PIC will be configured and ready to work.
  91
  92 \section{Disabling/enabling IRQs (OCW1)}
  93 \paragraph{}After initialization the main PIC functionallity can be controlled by two
  94 ports. They can be used to disable or enable specific IRQ the hardware way.
  95 These control registers are bit fields where each bit represents one of the
  96 IRQs. If bit is set IRQ is disabled. Accessing these registers can be done
  97 by using command OCW1 (operation control word) which can be send by
  98 reading and/or writing to ports \texttt{0x21} (master PIC) and \texttt{0xA1} (slave PIC). Master
  99 PIC controls IRQs 0-7, slave PIC controls IRQs 8-15.
 100
 101 \section{IRQs description}
 102 \begin{table}
 103 \begin{tabular}{ll}
 104 \textbf{IRQ} & \textbf{Device }\\
 105 0 & PIT \\
 106 1 & keyboard \\
 107 2 & slave PIC \\
 108 3 & second serial port \\
 109 4 & first serial port \\
 110 5 & hard disk controller \\
 111 6 & floppy disk controller \\
 112 7 & paraell port \\
 113 8 & real time clock \\
 114 9 & not used \\
 115 10 & not used \\
 116 11 & not used \\
 117 12 & ps/2 mouse \\
 118 13 & FPU \\
 119 14 & hard disk controller \\
 120 15 & hard disk controller
 121 \end{tabular}
 122 \caption{Devices assigned to specific IRQs}
 123 \label{irqs}
 124 \end{table}
 125
 126 \paragraph{}IRQs are used to allow hardware to inform CPU that some event has happened.
 127 Each IRQ is assigned to a certain device. Table \ref{irqs} shows which device calls which
 128 IRQ. Positions marked as \textit{not used} are reserved for PCI and/or other buses automatic
 129 configuration.
 130
 131 \end{document}