pet-projects/emu8086/src/RAMMemory.java

   1 import java.io.*;
   2
   3 /**
   4  * Emulates 8086-based computer RAM memory.
   5  *
   6  * @author Luiz Fernando N. Capitulino
   7  */
   8 public class RAMMemory implements Serializable {
   9         /**
  10          * RAM memory contents.
  11          */
  12         private short[] memory;
  13
  14         /**
  15          * Triggers InvalidMemException if addr is invalid
  16          *
  17          * @param addr memory address to check
  18          * @throws InvalidMemException
  19          */
  20         private void invalid_address(int addr) throws InvalidMemException
  21         {
  22                 if ((addr < 0) || (addr >= memory.length))
  23                         throw new InvalidMemException(addr);
  24         }
  25
  26         /**
  27          * Write all memory contents to stdout.
  28          */
  29         public void dump()
  30         {
  31                 for (int i = 0; i < memory.length; i++)
  32                         System.out.printf("%x   0x%x \n", i, memory[i]);
  33         }
  34
  35         /**
  36          * Print the contents of the specified address.
  37          *
  38          * @param addr RAM address to print contents
  39          */
  40         public void show(int addr)
  41         {
  42                 System.out.printf("[MEM 0x%x] 0x%x\n", addr, memory[addr]);
  43         }
  44
  45         /**
  46          * Write one byte into the specified RAM address.
  47          *
  48          * @param addr RAM address to write to
  49          * @param value new contents for the specified address
  50          * @throws InvalidMemException
  51          */
  52         public void write(int addr, short value) throws InvalidMemException
  53         {
  54                 invalid_address(addr);
  55                 memory[addr] = (short) (value & (short) 255);
  56         }
  57
  58         /**
  59          * Read one byte from the specified RAM address.
  60          *
  61          * @param addr RAM address to read from
  62          * @return address contents
  63          * @throws InvalidMemException
  64          */
  65         public short read(int addr) throws InvalidMemException
  66         {
  67                 invalid_address(addr);
  68                 return ((short) (memory[addr] & 255));
  69         }
  70
  71         /**
  72          * Constructor.
  73          *
  74          * @size RAM size in bytes.
  75          */
  76         public RAMMemory(int size)
  77         {
  78                 memory = new short[size];
  79         }
  80 }