jsos

college code for operating system fundamentals in js
memory.js

(3335B)
      1 /* ------------  
      2    CPU.js
      3 
      4    Requires global.js.
      5    
      6    Core Memory implementation.  
      7    In this manner, it's A LITTLE BIT like a hypervisor,
      8    in that the Document envorinment inside a browser is the "bare metal" (so to speak) for which we write code
      9    that hosts our client OS. But that analogy only goes so far, and the lines are blurred, because we are using
     10    JavaScript in both the host and client environments.
     11 
     12    This code references page numbers in the text book: 
     13    Operating System Concepts 8th editiion by Silberschatz, Galvin, and Gagne.  ISBN 978-0-470-12872-5
     14    ------------ */
     15 
     16 /* 
     17  * The core memory has an array to save bytes of data.
     18  * Bytes will be formatted as integers of 0-255, but 
     19  * outputs in hex format.
     20  */
     21 function memory(maxBytes) {
     22  
     23   /* The main container of bytes in memory. */
     24   this.memory = new Array();
     25 
     26   /* 
     27    * Whether it should update the output when 
     28    * a byte is set in memory.
     29    */
     30   var showOuput = true;
     31 
     32   /* Initializes the memory with zeros. */
     33   this.init = function() {
     34     for(var i=0; i<maxBytes; i++) {
     35       this.memory[i] = 0;
     36     }
     37     this.output();
     38   }
     39 
     40   /* 
     41    * Allocates an array of bytes starting from base.
     42    */
     43   this.allocateBytes = function(bytes, base) {
     44     this.showOutput = false;
     45 
     46     for(var i=0; i<bytes.length; i++) {
     47       this.setByte(bytes[i], base+i);
     48     }
     49 
     50     this.showOutput = true;
     51     this.output();
     52   }
     53 
     54   /* 
     55    * Deallocates an array of bytes starting from base.
     56    */
     57   this.deallocateBytes = function(base, limit) {
     58     var result = [];
     59     this.showOutput = false;
     60 
     61     for(var i=base; i<=limit; i++) {
     62       result[i-base] = this.getByte(i)
     63       this.setByte(0, i);
     64     }
     65 
     66     this.showOutput = true;
     67     this.output();
     68 
     69     return result;
     70   }
     71 
     72   /* 
     73    * Gets byte value in a location.
     74    */
     75   this.getByte = function(location) {
     76     if(!this.isValidLocation(location))
     77       krnTrapError(_ERROR_STACK_OVERFLOW);
     78     return this.memory[location];
     79   }
     80 
     81   /*
     82    * Allocate a byte in a location in memory.
     83    */
     84   this.setByte = function(byte, location) {
     85     if(!isByte(byte))
     86       krnTrapError(_ERROR_INVALID_BYTE_VALUE);
     87     if(!this.isValidLocation(location))
     88       krnTrapError(_ERROR_STACK_OVERFLOW);
     89     this.memory[location] = byte;
     90 
     91     if(showOuput) this.output();
     92   }
     93 
     94   /* Memory dump. */
     95   this.dumpMemory = function() {
     96     return this.memory;
     97   }
     98 
     99   /* 
    100    * Outputs memory dump to interface.
    101    */
    102   this.output = function() {
    103 
    104     // 8 columns
    105     function extract(dump) {
    106       var i=0;
    107       var html = "";
    108       for(var j=0; j < dump.length; j++) {
    109         if(i == 8) {
    110           i=0;
    111           html += '</tr>';
    112           if(j < dump.length) 
    113             html += '<tr><th align="right">'+
    114                 pad(j.toString(16),4).toUpperCase()+'</th>';
    115         }
    116         i++;
    117         html += '<td>'+
    118           pad(dump[j].toString(16),2).toUpperCase()+'</td>';
    119       } 
    120       return html;
    121     }
    122 
    123     var dump = this.dumpMemory();
    124     var html = '<tr><th>location</th></tr><tr>';
    125     html += '<th align="right">0000</th>';
    126     html += extract(dump);
    127     html += '</tr>'; 
    128     document.
    129         getElementById("memoryDumpTable").innerHTML = html;
    130   }
    131 
    132   /*
    133    * Checks if the location address is valid.
    134    */
    135   this.isValidLocation = function(location) {
    136     return location > -1 && location < maxBytes;
    137   }
    138 }