Why isn't VMWare copying the content of my drive to Memory Address 0x7C00? [OSDev]

[paikuhan]

Hi,

I created a simple "Master Boot Record" for my toy OS. The first sector (MBR) loads perfectly to memory address 0x7C00. At first I didn't know why, but I was finally able to use pointer to other memory addresses by adding these few line at the start of my nasm code:

CLI
MOV AX,CS ; Copy code segment
MOV DS,AX ; Make DS correct
MOV ES,AX ; Make ES correct
MOV SS,AX ; Make SS correct
MOV BP,0x7C00
MOV SP,0x7C00 ; SETUP A STACK
STI

Note that I don't need them with Bochs Emulator (I'm guessing because it's outdated?), but need them in both VMWare Player and Oracle VirtualBox. Then what I made my MBR do is to load itself at memory address 0x600 and jump to that address + skipping previously executed instructions. Up to this point everything is fine. Now to my issue: The next thing the code is supposed to do is load the partition's first sector to memory address 0x7C00 (where the old copy of the MBR resides) and jump back there but this doesn't happen. the old copy of the MBR is not overwritten and thus VMWare Player is looping between 0x7C00 and 0x600.

Here is my full code:

;********************************************************************;
;* START OF CODE *;
;********************************************************************;

%define SIZE 512 ; MBR sector size (512 bytes)
%define BASE 0x7C00 ; Address at which BIOS will load MBR
%define DEST 0x0600 ; Address at which MBR should be copied

;********************************************************************;
;* NASM settings *;
;********************************************************************;

[BITS 16] ; Enable 16-bit real mode
[ORG BASE] ; Set the base address for MBR

;********************************************************************;
;* Setup segment registers *;
;********************************************************************;
CLI
MOV AX,CS ; Copy code segment
MOV DS,AX ; Make DS correct
MOV ES,AX ; Make ES correct
MOV SS,AX ; Make SS correct
MOV BP,0x7C00
MOV SP,0x7C00 ; SETUP A STACK
STI ;IT WAS ORIGINALLY PUBLISHED ON HTTPS://WWW.APRIORIT.COM/

;********************************************************************;
;* Prepare registers *;
;********************************************************************;
MOV BX,Prepare
CALL print_string ; function that prints a string whose pointer is loaded in BX

XOR AX,AX
MOV DS,AX
MOV ES,AX
MOV SS,AX
MOV SP,BASE

;********************************************************************;
;* Copy MBR to DEST and jump there *;
;********************************************************************;
MOV BX,Copy
CALL print_string ; function that prints a string whose pointer is loaded in BX

MOV SI,BASE
MOV DI,DEST
MOV CX,SIZE
CLD
REP MOVSB

JMP DEST + SKIP ; When you ask to jump somewhere it will jump in absolute address
; For instance JMP 0x05 will jump to memory address 0x05 instead
; of 0x7C05

SKIP: EQU ($ - $$) ; Go here in copied code

MOV BX,Loading
CALL print_string ; function that prints a string whose pointer is loaded in BX

;Extended Read
MOV AH, 0x42
MOV AL, 3
;MOV DL,
MOV BX, 0
MOV DS, BX
MOV SI, DAP
MOV BX, 0x7C00
INT 0x13

JMP 0x7600 + 0x7C00

DAP:
DAP_SIZE: DB 0x10
UNUSED: DB 0x00
SECTOR_COUNT: DW 3 ; int 13 resets this to # of blocks actually read/written
SEGMENT_OFFSET: DD 0x7C00 ; memory buffer destination address (0:7c00)
LBA: DQ 2048 ; put the lba to read in this spot

%include "../../inc/chapter3/print_string.inc.asm" ; print string function is in an external file

Prepare: DB "Prepare registers.",10,13,0
Copy: DB "Copy MBR to DEST and jump there.",10,13,0
Loading: DB "Loading the partition bootsector.",10,13,0

TIMES 446-($-$$) DB 0

;********************************************************************;
;* END OF CODE *;
;********************************************************************;

Note that on the Bochs Emulator and on Oracle Virtualbox the old MBR is overwritten and there is no endless loop. What should I do to make VMWare Player copy the partition's first sector to memory 0x7C00.

Thanks in advance.