From 40065266f3e104082fca8c0d12c2bacd085ebd22 Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Mon, 20 Apr 2020 19:13:06 +0200
Subject: [PATCH] Implement int 29h: Fast console output

---
 boot/kernel.asm | 50 ++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 37 insertions(+), 13 deletions(-)

diff --git a/boot/kernel.asm b/boot/kernel.asm
index 482904b..7c94c61 100644
--- a/boot/kernel.asm
+++ b/boot/kernel.asm
@@ -6,7 +6,11 @@
 
 banner:	db "rdos", 0xA, 0xD, '$'
 
+	; Alias for Int 21h,AH=0h
 int20h:	xor ah, ah
+	; allow extenders to get away with only hooking 21h
+	jmp [cs:(0x21 * 4)]
+
 int21h:	; inside of kernel, direction always goes up
 	; the iret will restore it to the user value later
 	cld
@@ -30,7 +34,7 @@ int21h:	; inside of kernel, direction always goes up
 	pop bp
 	pop ax
 	; iret frame: IP CS FLAGS
-	iret
+iret:	iret
 
 	; Subfunction ptr
 	; this is used as extra register in int21h
@@ -72,12 +76,10 @@ putc:	push ax
 	; DOS 1+ 9h - WRITE STRING TO STANDARD OUTPUT
 	; IN	ds:dx	'$'-terminated string
 puts:	push si
-	mov ah, 0x0E
-	xor bx, bx
 .loop:	lodsb
 	cmp al, '$'
 	je .end
-	int 0x10
+	int 0x29
 	jmp .loop
 .end:	pop si
 	ret
@@ -202,11 +204,19 @@ ldbpb:	push ds
 	pop ds
 	ret
 
-main:	mov si, banner
-	mov ah, 0x09
-	int 0x21
-end:	hlt
-	jmp end
+	; DOS 2+ - FAST CONSOLE OUTPUT
+	; IN	al	character to print
+fputc:	push ax
+	push bx
+	mov ah, 0x0E
+	xor bx, bx
+	int 0x10
+	pop bx
+	pop ax
+	iret
+
+main:	hlt
+	jmp main
 
 init:	cli
 	xor ax, ax
@@ -220,14 +230,28 @@ init:	cli
 	mov cx, (init-$$)
 	rep movsb
 
+	; Set boot drive as current drive
 	call dnconv
 	call select
 
+	; Set int 0x20 to 0x2F
+	mov bx, ivects+0x7C00-$$
+	mov cx, 0x10
 	mov al, 0x20
-	mov dx, int20h
-	call setint
-	mov al, 0x21
-	mov dx, int21h
+.loop:	mov dx, [bx]
 	call setint
+	inc al
+	inc bx
+	inc bx
+	loop .loop
+
+	mov si, banner
+	mov ah, 0x09
+	int 0x21
 
 	jmp 0:main
+
+ivects:	dw int20h, int21h, iret, iret
+	dw iret, iret, iret, iret
+	dw iret, fputc, iret, iret
+	dw iret, iret, iret, iret