org.razvan.jzx
Class BaseMemory

java.lang.Object
  org.razvan.jzx.BaseComponent
      org.razvan.jzx.BaseMemory

Direct Known Subclasses:

Memory, Memory

public abstract class BaseMemory
extends BaseComponent

Base class extended by all memory components that comprise the emulator.

This class provides basic, common memory functionality for the memory subsystem of the emulator. Specific methods are overriden or implemented so as to comply with the Spectrum 48k and the Spectrum 128k models.

Author:

Razvan Surdulescu (c) 2001 - 2006, Erik Kunze (c) 1995, 1996, 1997, Des Herriott (c) 1993, 1994
You may use and distribute this software for free provided you include this copyright notice. You may not sell this software, use my name for publicity reasons or modify the code without permission from me.

See Also:

Memory, Memory

Field Summary

protected byte[][]	m_frame Maps the frame number to the physical page data.
protected int[]	m_frameToPage Maps a frame number to a physical page number.
protected byte[][]	m_page The full memory array.
protected BaseScreen	m_screen Cached reference to the screen component.
static int	PAGE_SIZE The size, in bytes, for a memory page.
static int	RAM0 The first RAM page.
static int	RAM1 The second RAM page.
static int	RAM2 The third RAM page.
static int	RAM3 The fourth RAM page.
static int	RAM4 The fifth RAM page.
static int	RAM5 The sixth RAM page.
static int	RAM6 The seventh RAM page.
static int	RAM7 The eighth RAM page.
static int	ROM0 The first ROM page.
static int	ROM1 The second ROM page.
static int	ROM2 The third ROM page.
static int	ROM3 The fourth ROM page.

Fields inherited from class org.razvan.jzx.BaseComponent

m_logger, m_spectrum

Constructor Summary

BaseMemory()

Method Summary

byte[]	getBytes(int page) Returns the byte array that comprises a particular page.
void	init(BaseSpectrum spectrum, ILogger logger) Allocate the memory arrays, cache the screen component and pages in the appropriate memory pages.
void	load(BaseLoader loader) Load the memory contents from the given BaseLoader object.
void	pageIn(int frame, int page) Maps a particular physical page into a given virtual frame number.
int	read16(int addr16) Reads a word starting at a particular 16-bit address.
int	read8(int addr16) Reads a byte from a particular 16-bit address.
protected void	readROM(java.lang.String name, byte[] page) Load the contents of a ROM file into the given memory page.
void	terminate() Sets the memory arrays to null and releases the cached screen reference.
java.lang.String	toString() Return a string representation of the memory state, which is useful for debugging.
void	write16(int addr16, int val16) Writes a word starting at a particular 16-bit address.
void	write8(int addr16, int val8) Writes a byte to a particular 16-bit address.

Methods inherited from class org.razvan.jzx.BaseComponent

getSpectrum, reset

Methods inherited from class java.lang.Object

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

Field Detail

PAGE_SIZE

public static final int PAGE_SIZE

The size, in bytes, for a memory page.

See Also:

Constant Field Values

ROM0

public static final int ROM0

The first ROM page.

See Also:

Constant Field Values

ROM1

public static final int ROM1

The second ROM page.

See Also:

Constant Field Values

ROM2

public static final int ROM2

The third ROM page.

See Also:

Constant Field Values

ROM3

public static final int ROM3

The fourth ROM page.

See Also:

Constant Field Values

RAM0

public static final int RAM0

The first RAM page.

See Also:

Constant Field Values

RAM1

public static final int RAM1

The second RAM page.

See Also:

Constant Field Values

RAM2

public static final int RAM2

The third RAM page.

See Also:

Constant Field Values

RAM3

public static final int RAM3

The fourth RAM page.

See Also:

Constant Field Values

RAM4

public static final int RAM4

The fifth RAM page.

See Also:

Constant Field Values

RAM5

public static final int RAM5

The sixth RAM page.

See Also:

Constant Field Values

RAM6

public static final int RAM6

The seventh RAM page.

See Also:

Constant Field Values

RAM7

public static final int RAM7

The eighth RAM page.

See Also:

Constant Field Values

m_frameToPage

protected int[] m_frameToPage

Maps a frame number to a physical page number.

There are four possible frame numbers (0 to 3.)

m_frame

protected byte[][] m_frame

Maps the frame number to the physical page data.

There are four possible frame numbers (0 to 3.)

m_page

protected byte[][] m_page

The full memory array.

The sixteen possible phisical pages (4 ROM pages and 12 RAM pages.)

m_screen

protected BaseScreen m_screen

Cached reference to the screen component.

This is used to update the screen whenever the appropriate memory area is modified.

Constructor Detail

BaseMemory

public BaseMemory()

Method Detail

init

public void init(BaseSpectrum spectrum,
                 ILogger logger)

Allocate the memory arrays, cache the screen component and pages in the appropriate memory pages.

Note that the cached screen reference can be null after this call, in the event that the BaseSpectrum parameter is itself null. This is allowed for "headless" memory objects that are not tied to a particular BaseSpectrum instance. This is used for loading the snapshot data into a memory instance, that is then copied directly into the physical BaseSpectrum memory instance.

Overrides:

init in class BaseComponent

See Also:

pageIn(int, int)

terminate

public void terminate()

Sets the memory arrays to null and releases the cached screen reference.

Overrides:

terminate in class BaseComponent

readROM

protected void readROM(java.lang.String name,
                       byte[] page)
                throws java.io.IOException

Load the contents of a ROM file into the given memory page.

The ROM file is specified as a Java Resource and loaded by means of Class.getResource(String).

Parameters:

name - The name of the resource where the ROM file resides.

page - The memory page into which to load the ROM file.

Throws:

java.io.IOException - Thrown if the resource is not found or an error occurs during reading.

pageIn

public void pageIn(int frame,
                   int page)

Maps a particular physical page into a given virtual frame number.

The method sets:

• m_frameToPage[frame] = page
• m_frame[frame] = m_page[page]

Parameters:

frame - The virtual frame number. You cannot map a RAM page into frame 0.

page - The physical page number.

getBytes

public byte[] getBytes(int page)

Returns the byte array that comprises a particular page.

read8

public int read8(int addr16)

Reads a byte from a particular 16-bit address.

The address is mapped into a frame number by taking the first two bits, and then frame number is then mapped into a physical page. The remaining address bits are used to index into the physical page.

Parameters:

addr16 - The 16-bit address to read from.

Returns:

Returns the 8 bits at the specified address.

write8

public void write8(int addr16,
                   int val8)

Writes a byte to a particular 16-bit address.

The address is mapped into a frame number by taking the first two bits, and then frame number is then mapped into a physical page. The remaining address bits are used to index into the physical page.

Nothing is written to a ROM page.

If the address falls into the memory mapped area of the screen memory, the screen object is updated appropriately.

Parameters:

addr16 - The 16-bit address to write to.

val8 - The 8 bits to write at the specified address.

read16

public int read16(int addr16)

Reads a word starting at a particular 16-bit address.

The method calls read8() for two consecutive addresses and collates the results.

Parameters:

addr16 - The 16-bit address to start reading from.

Returns:

Returns the 16 bits from the two consecutive addresses.

See Also:

read8(int)

write16

public void write16(int addr16,
                    int val16)

Writes a word starting at a particular 16-bit address.

The method calls write8() for two consecutive addresses, with the two halves of the specified argument.

Parameters:

addr16 - The 16-bit address to start writing to.

val16 - The 16 bits to start writing at the specified address.

See Also:

write16(int, int)

load

public void load(BaseLoader loader)

Load the memory contents from the given BaseLoader object.

The BaseLoader contains a "headless" memory object inside it, whose page contents are copied into the page contents of "this" memory object.

Specified by:

load in class BaseComponent

See Also:

BaseLoader

toString

public java.lang.String toString()

Return a string representation of the memory state, which is useful for debugging.

Overrides:

toString in class java.lang.Object