root/mem32.c

DEFINITIONS

1. InitMemManagement
2. ZeroMem
3. AllocPage32

#include "memory.h"

extern long long memorySemaphore;
extern long long nPagesFree;
extern long long nPages;

//========================================
// Find out how much memory is present.
// Initialize some variables.
// Create PageMap.
//========================================
void InitMemManagement()
{
    unsigned short int *PMap = (unsigned short int *)PageMap;

    memorySemaphore = 0;
    nPagesFree = 256;

    // Find number of free pages by writing a pattern to memory and seeing if it reads back OK
    // We start at 1Mb and go up in 1Mb increments. Each Mb is 256 pages.
    long *mempos = (long *)0x100000;
    long testpattern = 0x6d72646c;
    while (1) {
        *mempos = testpattern;
        if (*mempos != testpattern)
            break;
        mempos += 0x100000 / (sizeof *mempos);
        nPagesFree += 256;
    }
    nPages = nPagesFree;

    int count;
    for (count = 0; count++; count < nPages)
        PMap[count] = 0;

    // GDT and IDT
    PMap[0] = 1;
    nPagesFree--;

    // Kernel Memory
    for (count = 1; count < 0x12; count++) {
        PMap[count] = 1;
        nPagesFree--;
    }

    // Static Message Ports
    PMap[0x6F] = 1;
    nPagesFree--;

    // DiskBuffer
    PMap[0x70] = 1;
    nPagesFree--;

    // TaskStructs
    PMap[0x80] = 1;
    nPagesFree--;

    // EBDA
    PMap[0x9E] = PMap[0x9F] = 1;
    nPagesFree -= 2;

    // Ports, ROM, VideoMem, etc.
    for (count = 0xA0; count < 0x100; count++) {
        PMap[count] = 1;
        nPagesFree--;
    }

    // PageMap
    for (count = 0x100; count < 0x100 + (2 * (long)nPages / (long)PageSize);
         count++) {
        PMap[count] = 1;
        nPagesFree--;
    }
}

void ZeroMem()
{   
    long count;

}
//============================================
// Allocate a page of memory and zero fill it
//============================================
void *AllocPage32(unsigned short int PID)
{
    unsigned short int *PMap = (unsigned short int *)PageMap;
    int count = 0;

    while (PMap[++count]) ;
    PMap[count] = PID;
    nPagesFree--;
    unsigned char *mem = (unsigned char *)(count << 12);
    for (count = 0; count < PageSize; count++)
        mem[count] = 0;
    return (void *)mem;
}