Continuously print 'A' at boot

real_mode_boot_to_A.asm

; Continuously print 'A' at boot
;
; Tested with NASM version 2.15.04
;         and QEMU emulator version 5.1.0
;
; To compile:
;     nasm -f bin real_mode_boot_to_A.asm -o real_mode_boot_to_A.bin
;
; To run:
;     qemu-system-x86_64 real_mode_boot_to_A.bin
;
; To run and avoid seeing a warning:
;     qemu-system-x86_64 -drive format=raw,file=real_mode_boot_to_A.bin
;
;     ( https://unix.stackexchange.com/questions/276480/ )
;
; Resource: https://github.com/cfenollosa/os-tutorial



start:
    mov ah, 0x0e ; Teletype output ( https://en.wikipedia.org/wiki/INT_10H )
    mov al, 'A'  ; The character to print

print:
    int 0x10
    jmp print

times 510 - ($-$$) db 0 ; Pad the remaining of the first 510 bytes with 0
dw 0xaa55               ; Magic bytes required at end of boot sector



; License: Zero Clause BSD
; Copyright (C) 2020 by Costava
;
; Permission to use, copy, modify, and/or distribute this software for any
; purpose with or without fee is hereby granted.
;
; THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
; REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
; AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
; INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
; LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
; OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
; PERFORMANCE OF THIS SOFTWARE.