abstractstructure.java

来自「纯java操作系统jnode,安装简单和操作简单的个人使用的Java操作系统」· Java 代码 · 共 65 行

/*
 * $Id: AbstractStructure.java,v 1.1 2003/11/25 11:42:17 epr Exp $
 */
package org.jnode.driver.usb.uhci;

import org.jnode.system.MemoryResource;
import org.jnode.system.ResourceManager;
import org.jnode.vm.Address;

/**
 * Generic descriptor class, that supports memory alignment
 * of the structure itself.
 * 
 * @author Ewout Prangsma ([e-mail])
 */
public abstract class AbstractStructure {

	private final byte[] data;
	private final MemoryResource dataRes;
	private final int offset;
	private final int descrAddr;

	/**
	 * Create a new instance
	 * @param rm The resource manager
	 * @param size The size of the descriptor in bytes
	 * @param alignment The alignment of the descriptor in bytes
	 */
	protected AbstractStructure(ResourceManager rm, int size, int alignment) {
		this.data = new byte[size + alignment];
		this.dataRes = rm.asMemoryResource(data);
		Address ptr = dataRes.getAddress();
		int offset = 0;
		while (((offset + Address.as32bit(ptr)) & (alignment-1)) != 0) {
			offset++;
		}
		this.offset = offset;
		this.descrAddr = Address.as32bit(dataRes.getAddress()) + offset;
	}
	
	/**
	 * Get a 32-bit integer at the given offset out of the descriptor
	 * @param ofs
	 */
	protected final int getInt(int ofs) {
		return dataRes.getInt(this.offset + ofs);
	}
	
	/**
	 * Set a 32-bit integer at the given offset into the descriptor
	 * @param ofs
	 * @param value
	 */
	protected final void setInt(int ofs, int value) {
		dataRes.setInt(this.offset + ofs, value);
	}
	
	/**
	 * Gets the address (in physical memory) of the start of the descriptor.
	 */
	public int getDescriptorAddress() {
		return descrAddr;
	}
}