; SPDX-License-Identifier: WTFPL
; nasm sertest.asm -o sertest.img

	section	.text
	use16

	jmp short start
	nop

	; disk description table (to emulate floppy)
	db "TESTCODE"		; OEMLabel
	dw 512			; BytesPerSector
	db 1			; SectorsPerCluster
	dw 1			; ReservedForBoot
	db 2			; NumberOfFats
	dw 224			; RootDirEntries
	dw 2880			; LogicalSectors
	db 0f0h			; MediumByte
	dw 9			; SectorsPerFat
	dw 18			; SectorsPerTrack
	dw 2			; Sides
	dd 0			; HiddenSectors
	dd 0			; LargeSectors
	dw 0			; DriveNo
	db 41			; Signature
	dd 0			; VolumeID
	db "TESTCODE000"	; VolumeLabel
	db "FAT12   "		; FileSystem

start:
	xor dx, dx		; com0
	mov al, '>'
	call put_char

wait_for_key:	
	xor ah, ah
	int 16h
	cmp al, '0'
	jb wait_for_key
	cmp al, '7'
	jg wait_for_key
	call put_char
	; bit[0:3] of al: baudrate value
	; 000 110
	; 001 150
	; 010 300
	; 011 600
	; 100 1200
	; 101 2400
	; 110 4800
	; 111 9600

set_baudrate:
	shl al, 5
	or al, 03h
	xor ah, ah
	int 14h

	mov cx, 64

wait_for_tx:
	mov ah, 3
	int 14h
	test ah, 20h
	jz wait_for_tx

send_character:
	mov al, 'U'
	mov ah, 1
	int 14h

	loop wait_for_tx

	jmp wait_for_key

put_char:
	mov ah, 0eh
	xor bh, bh
	int 10h
	ret

	; end of boot sector and blank contents
	times 510 - ($ - $$) db 0
	dw 0aa55h

	times (2879 * 512) db 0xe5