[syslinux] [PATCH] isohdpfx: Ctrl-key press forces load from first hard disk

[TJ]

---
 mbr/isohdpfx.S |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/mbr/isohdpfx.S b/mbr/isohdpfx.S
index 9e9d55c..cccdcc9 100644
--- a/mbr/isohdpfx.S
+++ b/mbr/isohdpfx.S
@@ -67,6 +67,7 @@ _start:
 	movw	%ax, %ss
 	movw	$stack, %sp
 	movw	%sp, %si
+	movw	%sp, %bp	/* needed later if drive number is to be forced due to Ctrl key being pressed */
 	pushw	%es		/* es:di -> $PnP header */
 	pushw	%di
 	pushw	%dx		/* dl -> drive number */
@@ -82,7 +83,18 @@ _start:
 	ljmpw	$0, $next
 
 next:
+	/* Provide a way for the user to force boot from first hard-disk by pressing a Ctrl key */
+get_shift_keys:	
+	movb	$0x02, %ah		/* function: get keyboard shift flags */
+	int		$0x16			/* read keys; shift flags returned in AL */
+	testb	$0x04, %al		/* control key pressed? */
+	jz		detect_bios_type
+force_first_hard_disk:
+	movb 	$0x80, -6(%bp)	/* offset from top-of-stack to drive number; force it to be first hard disk */
+
+detect_bios_type:
 	/* Check to see if we have EBIOS */
+	movw	(driveno), %dx
 	pushw	%dx		/* drive number */
 	movb	$0x41, %ah	/* %al == 0 already */
 	movw	$0x55aa, %bx
-- 
1.6.0.4