nachos.machine
Class Processor

java.lang.Object
  nachos.machine.Processor

public final class Processor
extends Object

The Processor class simulates a MIPS processor that supports a subset of the R3000 instruction set. Specifically, the processor lacks all coprocessor support, and can only execute in user mode. Address translation information is accessed via the API. The API also allows a kernel to set an exception handler to be called on any user mode exception.

The Processor API is re-entrant, so a single simulated processor can be shared by multiple user threads.

An instance of a Processor also includes pages of physical memory accessible to user programs, the size of which is fixed by the constructor.

Field Summary

static int	exceptionAddressError Caused by an access to a misaligned virtual address.
static int	exceptionBusError Caused by an access to an invalid physical page.
static int	exceptionIllegalInstruction Caused by an attempt to execute an illegal instruction.
static String[]	exceptionNames The names of the CPU exceptions.
static int	exceptionOverflow Caused by an overflow by a signed operation.
static int	exceptionPageFault Caused by an access to an invalid virtual page.
static int	exceptionReadOnly Caused by a write access to a read-only virtual page.
static int	exceptionSyscall Caused by a syscall instruction.
static int	exceptionTLBMiss Caused by an access to a virtual page not mapped by any TLB entry.
static int	maxPages Number of pages in a 32-bit address space.
static int	numUserRegisters The total number of software-accessible CPU registers.
static int	pageSize Size of a page, in bytes.
static int	regA0 Index of argument register 0.
static int	regA1 Index of argument register 1.
static int	regA2 Index of argument register 2.
static int	regA3 Index of argument register 3.
static int	regBadVAddr Index of the exception bad virtual address register.
static int	regCause Index of the exception cause register.
static int	regHi Index of the high register, used for multiplication and division.
static int	regLo Index of the low register, used for multiplication and division.
static int	regNextPC Index of the next program counter register.
static int	regPC Index of the program counter register.
static int	regRA Index of the return address register.
static int	regSP Index of the stack pointer register.
static int	regV0 Index of return value register 0.
static int	regV1 Index of return value register 1.

Constructor Summary

Processor(Privilege privilege, int numPhysPages)
Allocate a new MIPS processor, with the specified amount of memory.

Method Summary

void	advancePC() Advance the PC to the next instruction.
Runnable	getExceptionHandler() Get the exception handler, set by the last call to setExceptionHandler().
byte[]	getMemory() Return a reference to the physical memory array.
int	getNumPhysPages() Return the number of pages of physical memory attached to this simulated processor.
TranslationEntry[]	getPageTable() Get the current page table, set by the last call to setPageTable().
int	getTLBSize() Return the number of entries in this processor's TLB.
boolean	hasTLB() Test whether this processor uses a software-managed TLB, or single-level paging.
static int	makeAddress(int page, int offset) Concatenate a page number and an offset into an address.
static int	offsetFromAddress(int address) Extract the offset component from an address.
static int	pageFromAddress(int address) Extract the page number component from a 32-bit address.
int	readRegister(int number) Read and return the contents of the specified CPU register.
TranslationEntry	readTLBEntry(int number) Returns the specified TLB entry.
void	run() Start executing instructions at the current PC.
void	setExceptionHandler(Runnable exceptionHandler) Set the exception handler, called whenever a user exception occurs.
void	setPageTable(TranslationEntry[] pageTable) Set the page table pointer.
void	writeRegister(int number, int value) Write the specified value into the specified CPU register.
void	writeTLBEntry(int number, TranslationEntry entry) Fill the specified TLB entry.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

exceptionSyscall

public static final int exceptionSyscall

Caused by a syscall instruction.

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Constant Field Values

exceptionPageFault

public static final int exceptionPageFault

Caused by an access to an invalid virtual page.

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exceptionTLBMiss

public static final int exceptionTLBMiss

Caused by an access to a virtual page not mapped by any TLB entry.

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exceptionReadOnly

public static final int exceptionReadOnly

Caused by a write access to a read-only virtual page.

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exceptionBusError

public static final int exceptionBusError

Caused by an access to an invalid physical page.

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exceptionAddressError

public static final int exceptionAddressError

Caused by an access to a misaligned virtual address.

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exceptionOverflow

public static final int exceptionOverflow

Caused by an overflow by a signed operation.

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exceptionIllegalInstruction

public static final int exceptionIllegalInstruction

Caused by an attempt to execute an illegal instruction.

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exceptionNames

public static final String[] exceptionNames

The names of the CPU exceptions.

regV0

public static final int regV0

Index of return value register 0.

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regV1

public static final int regV1

Index of return value register 1.

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regA0

public static final int regA0

Index of argument register 0.

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regA1

public static final int regA1

Index of argument register 1.

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regA2

public static final int regA2

Index of argument register 2.

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regA3

public static final int regA3

Index of argument register 3.

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regSP

public static final int regSP

Index of the stack pointer register.

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regRA

public static final int regRA

Index of the return address register.

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regLo

public static final int regLo

Index of the low register, used for multiplication and division.

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regHi

public static final int regHi

Index of the high register, used for multiplication and division.

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regPC

public static final int regPC

Index of the program counter register.

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regNextPC

public static final int regNextPC

Index of the next program counter register.

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regCause

public static final int regCause

Index of the exception cause register.

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regBadVAddr

public static final int regBadVAddr

Index of the exception bad virtual address register.

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numUserRegisters

public static final int numUserRegisters

The total number of software-accessible CPU registers.

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pageSize

public static final int pageSize

Size of a page, in bytes.

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maxPages

public static final int maxPages

Number of pages in a 32-bit address space.

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Constructor Detail

Processor

public Processor(Privilege privilege,
                 int numPhysPages)

Allocate a new MIPS processor, with the specified amount of memory.

Parameters:

privilege - encapsulates privileged access to the Nachos machine.

numPhysPages - the number of pages of physical memory to attach.

Method Detail

setExceptionHandler

public void setExceptionHandler(Runnable exceptionHandler)

Set the exception handler, called whenever a user exception occurs.

When the exception handler is called, interrupts will be enabled, and the CPU cause register will specify the cause of the exception (see the exception* constants).

Parameters:

exceptionHandler - the kernel exception handler.

getExceptionHandler

public Runnable getExceptionHandler()

Get the exception handler, set by the last call to setExceptionHandler().

Returns:

the exception handler.

run

public void run()

Start executing instructions at the current PC. Never returns.

readRegister

public int readRegister(int number)

Read and return the contents of the specified CPU register.

Parameters:

number - the register to read.

Returns:

the value of the register.

writeRegister

public void writeRegister(int number,
                          int value)

Write the specified value into the specified CPU register.

Parameters:

number - the register to write.

value - the value to write.

hasTLB

public boolean hasTLB()

Test whether this processor uses a software-managed TLB, or single-level paging.

If false, this processor directly supports single-level paging; use setPageTable().

If true, this processor has a software-managed TLB; use getTLBSize(), readTLBEntry(), and writeTLBEntry().

Using a method associated with the wrong address translation mechanism will result in an assertion failure.

Returns:

true if this processor has a software-managed TLB.

getPageTable

public TranslationEntry[] getPageTable()

Get the current page table, set by the last call to setPageTable().

Returns:

the current page table.

setPageTable

public void setPageTable(TranslationEntry[] pageTable)

Set the page table pointer. All further address translations will use the specified page table. The size of the current address space will be determined from the length of the page table array.

Parameters:

pageTable - the page table to use.

getTLBSize

public int getTLBSize()

Return the number of entries in this processor's TLB.

Returns:

the number of entries in this processor's TLB.

readTLBEntry

public TranslationEntry readTLBEntry(int number)

Returns the specified TLB entry.

Parameters:

number - the index into the TLB.

Returns:

the contents of the specified TLB entry.

writeTLBEntry

public void writeTLBEntry(int number,
                          TranslationEntry entry)

Fill the specified TLB entry.

The TLB is fully associative, so the location of an entry within the TLB does not affect anything.

Parameters:

number - the index into the TLB.

entry - the new contents of the TLB entry.

getNumPhysPages

public int getNumPhysPages()

Return the number of pages of physical memory attached to this simulated processor.

Returns:

the number of pages of physical memory.

getMemory

public byte[] getMemory()

Return a reference to the physical memory array. The size of this array is pageSize * getNumPhysPages().

Returns:

the main memory array.

makeAddress

public static int makeAddress(int page,
                              int offset)

Concatenate a page number and an offset into an address.

Parameters:

page - the page number. Must be between 0 and (2³² / pageSize) - 1.

offset - the offset within the page. Must be between 0 and pageSize - 1.

Returns:

a 32-bit address consisting of the specified page and offset.

pageFromAddress

public static int pageFromAddress(int address)

Extract the page number component from a 32-bit address.

Parameters:

address - the 32-bit address.

Returns:

the page number component of the address.

offsetFromAddress

public static int offsetFromAddress(int address)

Extract the offset component from an address.

Parameters:

address - the 32-bit address.

Returns:

the offset component of the address.

advancePC

public void advancePC()

Advance the PC to the next instruction.

Transfer the contents of the nextPC register into the PC register, and then add 4 to the value in the nextPC register. Same as advancePC(readRegister(regNextPC)+4).

Use after handling a syscall exception so that the processor will move on to the next instruction.