package org.jscsi.target.scsi.cdb;

 import java.nio.ByteBuffer;

 import org.jscsi.target.util.ReadWrite;

 /**

  * This class represents Command Descriptor Blocks for the <code>READ (6)

  * </code> SCSI command.

  * <p>

  * The READ (6) command requests that the device server read the specified logical block(s) and transfer them to the

  * data-in buffer. Each logical block read includes user data and, if the medium is formatted with protection

  * information enabled, protection information. Each logical block transferred includes user data but does not include

  * protection information.

  * <p>

  * Although the READ (6) command is limited to addressing up to 2,097,151 logical blocks, this command has been

  * maintained as mandatory since some system initialization routines require that the READ (6) command be used. System

  * initialization routines should migrate from the READ (6) command to the READ (10) command, which is capable of

  * addressing 4,294,947,295 logical blocks, or the READ (16) command, which is capable of addressing

  * 18,446,744,073,709,551,615 logical blocks.

  * 

  * @author Andreas Ergenzinger

  */

 public class Read6Cdb extends ReadCdb {

     public Read6Cdb (ByteBuffer buffer) {

         super(buffer);

     }

     @Override

     protected long deserializeLogicalBlockAddress (ByteBuffer buffer) {

         // the first three bits of byte 1 are reserved i.e. must be 0

         // check that

         final byte b = buffer.get(1);

         if (((b >> 5) & 7) != 0) addIllegalFieldPointer(1);

         // read the field's value

         return ((b & 31) << 16) | ReadWrite.readTwoByteInt(buffer, 2);

     }

     @Override

     protected int deserializeTransferLength (ByteBuffer buffer) {

         /*

          * A TRANSFER LENGTH field set to zero specifies that 256 logical blocks shall be read. Any other value

          * specifies the number of logical blocks that shall be read.

          */

         final int value = ReadWrite.readOneByteInt(buffer, 4);

         if (value == 0) return 256;

         return value;

     }

     @Override

     protected int getLogicalBlockAddressFieldIndex () {

         return 1;

     }

     @Override

     protected int getTransferLengthFieldIndex () {

         return 4;

     }

 }