Implement int 0x21 AH = 0x09, write string to stdout

src/int21/0.s

@@ -27,7 +27,27 @@ wrout:
 	mov dl, ' ' ; "tabs are expanded to blanks"
 .print:
 	mov al, dl
-	mov bl, 0x70
 	call print_character
 	pop bx
 	ret
+
+; AH = 0x09
+; write string to stdout
+; inputs:
+; 	DS:DX: pointer to '$'-terminated string
+; outputs:
+; 	AL: 0x24 ('$')
+wrout_str:
+	push si
+	mov si, dx
+	jmp .start_loop
+.print_loop:
+	mov dl, byte [si]
+	call wrout
+	inc si
+.start_loop:
+	cmp byte [si], '$'
+	jnz .print_loop
+	mov al, '$'
+	pop si
+	ret

src/int21/int21.s

@@ -30,7 +30,7 @@ nul:	stc
 ; TODO figure out a way to format this table. maybe it can be autogenerated?
 ; this table is misaligned for me and im the one who made it
 	;	x0	x1	x2	x3	x4	x5	x6	x7	x8	x9	xA	xB	xC	xD	xE	xF
-fn:	dw	nul,	rdin_echo,	wrout,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul	; 0x
+fn:	dw	nul,	rdin_echo,	wrout,	nul,	nul,	nul,	nul,	nul,	nul,	wrout_str,	nul,	nul,	nul,	nul,	nul,	nul	; 0x
 	dw	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul	; 1x
 	dw	nul,	nul,	nul,	nul,	nul,	setint,	nul,	nul,	nul,	nul,	nul,	nul,	gettime,	settime,	setverify,	nul	; 2x
 	dw	getver,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul,	nul	; 3x

src/kernel.s

@@ -7,12 +7,8 @@ kjmp: ; MUST be a jmp due to loader config
 %include "int21/int21.s"
 
 kernel_entry:
-	mov si, hello_string
-	mov bl, 0x70
-	call print_string
-
-	mov ah, 0x2
-	mov dl, '!'
+	mov ah, 0x9
+	mov dx, hello_string
 	int 0x21
 
 	jmp $