2-Stage x86 bootloader with boot loop

=====[stage1.asm]==================================================

[BITS 16]    ;16-bit real mode
[ORG 0x7C00] ;program origin

JMP start

msg_halt  DB "HALT0",0x00
msg_ok    DB "OK",0x0D,0x0A,0x00
msg_fail  DB "FAIL",0x0D,0x0A,0x00
msg_reset DB "Resetting Disk...",0x00
msg_read  DB "Reading Sector...",0x00
msg_st1   DB "Welcome to stage 1",0x0D,0x0A,0x00
msg_exit  DB "Now leaving stage 1",0x0D,0x0A,0x0D,0x0A,0x00

currentDrive DB 0x00 ;Drive number
;---------------
;Halt the system
;---------------
fn_halt:
    MOV SI,msg_halt
    CALL fn_print
  _halt:
    CLI
    HLT
    JMP _halt

;---------------------------------------------------------
;Print null-terminated string with address in SI to screen
;---------------------------------------------------------
fn_print:
    PUSH AX
    PUSH BX
  _print:
    LODSB
    OR AL,AL
    JZ _printDone
    MOV AH,0x0E
    MOV BH,0x00
    MOV BL,0x0F
    INT 0x10
    JMP _print
  _printDone:
    POP BX
    POP AX
    RET

;------------------------------
;Reset hdd back to first sector
;------------------------------
fn_reset_disk:
    PUSH AX
    PUSH DX

    MOV SI,msg_reset
    CALL fn_print

  _reset_disk:
    MOV AH,0x00               ;Reset drive
    MOV DL,BYTE[currentDrive] ;Drive number
    INT 0x13                  ;Video BIOS interrupt
    JC _reset_disk            ;Retry on fail

    MOV SI,msg_ok
    CALL fn_print

    POP DX
    POP AX
    RET

;--------------------------------------------
;Read a sector from the disk to 0x0500:0x0000
;--------------------------------------------
fn_read_sector:
    MOV DI,0x05
    MOV AX,0x0500             ;Location of stage 2
    MOV ES,AX                 ;Populate buffer secment
    XOR BX,BX                 ;Clear buffer offset

    MOV SI,msg_read
    CALL fn_print

  _try_read:
    MOV AH,0x02               ;Read from drive
    MOV AL,1                  ;How many sectors to read
    MOV CH,0                  ;Track/Cylinder number
    MOV CL,2                  ;Sector to read
    MOV DH,0                  ;Head number
    MOV DL,BYTE[currentDrive] ;Drive number
    INT 0x13
    JNC _read_done
    DEC DI
    CMP DI,0
    JZ  _read_error
    JMP _try_read
  _read_error:
    MOV SI,msg_fail
    CALL fn_print
    CALL fn_halt
    CLI
    HLT
  _read_done:
    MOV SI,msg_ok
    CALL fn_print
    RET

start:
    MOV [currentDrive],dl ;Save drive number
    CLI                   ;Disable interrupts while setting up the stack
    XOR AX,AX             ;Real mode flat memory model
    MOV DS,AX
    MOV ES,AX
    MOV FS,AX
    MOV GS,AX
    MOV SS,AX
    MOV SP,0xFFFF
    STI                   ;Enable interrupts

    MOV AH,0x00           ;Set video mode
    MOV AL,0x12           ;640x480x8 @ 80x30
    INT 0x10              ;Video BIOS interrupt

    MOV SI,msg_st1
    CALL fn_print

    CALL fn_reset_disk
    CALL fn_read_sector

    MOV SI,msg_exit
    CALL fn_print
    JMP  0x0500:0x0000

    CALL fn_halt

    CLI
    HLT

TIMES 510-($-$$) HLT         ;Padding bytes
DB    0x55, 0xAA             ;Mark bootable



=====[stage2.asm]==================================================

[BITS 16]    ;16-bit real mode
[ORG 0x5000] ;program origin

JMP main

%include "gdt.inc" ;Global Descriptor Table definition

msg_halt  DB "HALT1",0x00
msg_ok    DB "OK",0x0D,0x0A,0x00
msg_st2   DB "Welcome to Stage 2",0x0D,0x0A,0x00
msg_gdt   DB "Setting up GDT...",0x00
msg_a20   DB "Enabling A20 Gate...",0x00
msg_pm    DB "Entering Protected Mode...",0x00

;---------------
;Halt the system
;---------------
fn_halt:
    MOV SI,msg_halt
    CALL fn_print
  _halt:
    CLI
    HLT
    JMP _halt

;---------------------------------------------------------
;Print null-terminated string with address in SI to screen
;---------------------------------------------------------
fn_print:
    PUSH AX
    PUSH BX
  _print:
    LODSB
    OR AL,AL
    JZ _printDone
    MOV AH,0x0E
    MOV BH,0x00
    MOV BL,0x0F
    INT 0x10
    JMP _print
  _printDone:
    POP BX
    POP AX
    RET

fn_enable_A20:
  MOV AX,0x2401
  INT 0x15
  RET

main:
    CLI                   ;Disable interrupts while setting up the stack
    XOR AX,AX             ;Real mode flat memory model
    MOV DS,AX
    MOV ES,AX
    MOV FS,AX
    MOV GS,AX
    MOV SS,AX
    MOV SP,0xFFFF
    STI                   ;Enable interrupts

    MOV SI,msg_st2
    CALL fn_print

    MOV SI,msg_gdt
    CALL fn_print
    CALL fn_load_gdt
    MOV SI,msg_ok
    CALL fn_print

    MOV SI,msg_a20
    CALL fn_print
    CALL fn_enable_A20
    MOV SI,msg_ok
    CALL fn_print

    MOV SI,msg_pm
    CALL fn_print
    MOV EAX,CR0
    OR  EAX,1
    MOV CR0,EAX
    MOV SI,msg_ok
    CALL fn_print

    CALL fn_halt

TIMES 510-($-$$) HLT         ;Padding bytes


=====[gdt.inc]==================================================
fn_load_gdt:
                cli                             ;disable interrupts
                pusha                           ;save registers
                lgdt    [gdt_ptr]               ;load the gdt
                sti                             ;enable interrupts
                popa                            ;restore registers
                ret                             ;return

descriptor_table:
        ;null descriptor
                db      0                       ;fill 8 bytes with zeros
                db      0

        ;code descriptor
                dw      0FFFFH                  ;limit low
                dw      0                       ;base low
                db      0                       ;base middle
                db      10011010b               ;access
                db      11001111b               ;granularity
                db      0                       ;base high

        ;data descriptor
                dw      0FFFFH                  ;limit low
                dw      0                       ;base low
                db      0                       ;base middle
                db      10010010b               ;access
                db      11001111b               ;granularity
                db      0                       ;base high
end_table:
gdt_ptr:
                dw      end_table - descriptor_table - 1                ;the sise of the descriptor table - 1
                dd      descriptor_table                                ;base of the GDT