root/memory32.s

        .include "memory.inc"

        .global InitMemManagement
        .global AllocPage

        .text

        .code32

#==================================
# Find top of memory
#==================================
InitMemManagement:
        movw $0, (memorySemaphore)
        movl $0, NoOfAllocations
        movl $256, nPagesFree
        mov $0x0019FFFC, %eax
        mov $0, %ebx
        mov $0x6d72646c, %ecx
MemLoop:
        mov %ecx, (%eax)
        mov (%eax), %ebx
        cmp %ebx, %ecx
        jne MemLoopEnd
        add $0x00060003, %eax
        mov %eax, oMemMax
        sub $0x00060003, %eax
        add $0x00100000, %eax
        addl $256, nPagesFree
        mov $0, %ebx
        jmp MemLoop
MemLoopEnd:
        mov $0x00004000, %ecx
.a:     movb $0, PageMap(%ecx)
        loop .a
        # Mark used memory in MemoryMap
        # all this is defined as belonging to Task 1

        # GDT and IDT
        movb $1, PageMap
        decl nPagesFree

        # OS Memory
        # mov ecx, DataSegLen
        mov $0x1000, %ecx
        shr $0xB, %ecx
        add $2, %ecx              # # of pages in OS data segment
        add $0xF, %ecx            # # of pages in OS code segment
        mov $PageMap, %ebx
.again: 
        movb $1, (%ebx)
        inc %ebx
        decl nPagesFree
        loop .again

        # 0x0006F000 - 0x0006FFFF Static Message Ports
        movb $1, PageMap + 0x6F

        # 0x00070000 - 0x00071000 Disk Buffer
        movb $1, PageMap + 0x70

        # 0x0007F000 - 0x0007FFFF Page Map
        movb $1, PageMap + 0x7F

        # 0x00080000 - 0x00081000, TaskStructs
        movb $1, PageMap + 0x80
        mov  $0x80000, %ebx
        mov  $0x1000, %ecx
.again3:
        movb $0, (%ebx, %ecx)
        loop .again3

        # 0x000A0000 - 0x00100000, Ports, ROM, VideoMem, etc.
        mov $(PageMap + 0xA0), %ebx
        mov $0x60, %ecx
.ag2:   movb $1, (%ebx)
        inc %ebx
        decl nPagesFree
        loop .ag2

        # 0x001F0000 - 0x00200000, Shared Memory
        mov $(PageMap + 0x1F0), %ebx
        mov $0x10, %ecx
.ag3:   movb $1, (%ebx)
        inc %ebx
        decl nPagesFree
        loop .ag3

        ret

#===========================================
# Allocate a page of memory
# AL = task to allocate memory to
# if EAX = 0xFF then memory is for PT
# 0 fill the page
# return in EAX the Physical Memory address
#===========================================
AllocPage:
        push %ebx
        push %ecx
        # find first free page of Physical Memory
        mov $0, %ebx
.again2: cmpb $0, PageMap(%ebx)
        je .found
        inc %ebx
        jmp .again2
        # mark page as in use
.found: mov %al, PageMap(%ebx)
        # compute Physical Address
        xchg %eax, %ebx
        shl $12, %eax
        decl nPagesFree
        #mov  %eax, %ebx
        mov  $0x1000, %ecx
.again4:
        movb $0, (%eax, %ecx)
        loop .again4
        pop %ecx
        pop %ebx
        ret