From af5df85c16cf66d8d9aec3cdb3150c42f69a529c Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Sat, 26 Dec 2020 20:54:39 +0000
Subject: [PATCH] Use ebios extensions if enabled

---
 kernel/drive.asm | 42 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 7 deletions(-)

diff --git a/kernel/drive.asm b/kernel/drive.asm
index 9e09c75..3418217 100644
--- a/kernel/drive.asm
+++ b/kernel/drive.asm
@@ -13,9 +13,11 @@ dsknum:		resb 1
 		; bios drive we end up using
 biosnum:	resb 1
 
+dap:		resw 2
+.buf:		resw 2
 		; current sector number
 		; absolute, ignores partition
-dskseek:	resd 1
+dskseek:	resd 2
 
 		; bit 0 (1) - dirty flag for dskbuf
 		; bit 1 (2) - controller configured
@@ -69,7 +71,10 @@ int13:		; debug output
 		; read BIOS int13h/AH=8 values
 		; DPT data gets copied over our dpt
 		; CHS data gets inserted into our bpb
-getprm:		mov ah, 8
+getprm:		test byte [dskflag], 4
+		jnz .nodpt
+		; do the query
+		mov ah, 8
 		mov dl, [biosnum]
 		call int13
 		; bail out if error
@@ -159,9 +164,26 @@ loghdd:		sub dl, 2
 		cmp dl, 4
 		jnc logerr
 		push dx
-		mov byte [biosnum], 0x80
+		mov dl, 0x80
+		mov byte [biosnum], dl
+		; test for ebios extensions
+		mov ah, 0x41
+		mov bx, 0x55AA
+		call int13
+		sbb bx, 0xAA55
+		jnz .chs
+		; enable ebios and assume controller is configured
+		or byte [dskflag], (2+4)
+		; initialize DAP
+		mov word [dap], 0x1000
+		mov word [dap+2], 1
+		mov word [dap+4], dskbuf
+		xor ax, ax
+		mov word [dap+6], ax
+		mov word [dap+12], ax
+		mov word [dap+14], ax
 		; get chs data (needed or we cant load vbr)
-		call getprm
+.chs:		call getprm
 		; read mbr
 		xor ax, ax
 		xor dx, dx
@@ -244,9 +266,15 @@ _read:		mov ch, 2
 		db 0x3D ; cmp ax, imm16: causes next instr to be skipped
 _write:		mov ch, 3
 		mov cl, 1 ; read len
-		; TODO: do ebios i/o
+		; check if ebios supported
+		test byte [dskflag], 4
+		jz .l00
+		mov ax, cx
+		or ah, 0x40
+		mov si, dap
+		jmp .do
 		; check if we can skip controller reset
-		test byte [dskflag], 2
+.l00:		test byte [dskflag], 2
 		jnz .l01
 		; do controller reset
 		mov dl, [biosnum]
@@ -280,8 +308,8 @@ _write:		mov ch, 3
 		xchg ax, cx
 		xchg cx, dx
 		xchg dh, dl
-		mov dl, [biosnum]
 		mov bx, dskbuf
+.do:		mov dl, [biosnum]
 		; ah: subfunction selected via cx previously
 		; al: 1 = reading 1 sector
 		; cx: sector and cylinder number