From d1152995087544432268a349055a247488a6b99e Mon Sep 17 00:00:00 2001
From: Ry <ryanst755@gmail.com>
Date: Thu, 3 Nov 2022 19:10:54 -0700
Subject: [PATCH] Implement int 0x21 AH = 0x02, write character to stdout

---
 src/int21/0.s | 18 ++++++++++++++++--
 src/vga.s     | 17 +++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/int21/0.s b/src/int21/0.s
index 9fab32e..ce2c3e1 100644
--- a/src/int21/0.s
+++ b/src/int21/0.s
@@ -7,9 +7,23 @@
 ; outputs:
 ; 	AL: character read from stdin
 rdin_echo:
-	push ax
 	mov ah, 8
 	int 0x21
 	; TODO does echo go to stdout or to screen?
-	pop ax
+	ret
+
+; AH = 0x02
+; write character to stdout
+; inputs:
+; 	DL: character
+; outputs:
+; 	AL: last character output
+wrout:
+	; TODO handle ^C and stuff
+	; TODO handle stdout properly
+	push bx
+	mov al, dl
+	mov bl, 0x70
+	call print_character
+	pop bx
 	ret
diff --git a/src/vga.s b/src/vga.s
index 32aa442..46389e3 100644
--- a/src/vga.s
+++ b/src/vga.s
@@ -1,3 +1,20 @@
+; print a character to the screen
+; inputs:
+; 	AL: ASCII character
+; outputs:
+; 	none
+print_character:
+	push ax
+	push bx
+
+	mov ah, 0x0E
+	mov bh, 0x00
+	int 0x10
+
+	pop bx
+	pop ax
+	ret
+
 ; print a string to the screen
 ; inputs:
 ; 	DS:SI: pointer to '$'-terminated string