[syslinux] [PATCH 3/3] v2: isohdpfx: Ctrl-key press forces load from first hard disk

[TJ]

---
 mbr/isohdpfx.S |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/mbr/isohdpfx.S b/mbr/isohdpfx.S
index 9e9d55c..bddb533 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 */
@@ -82,6 +83,15 @@ _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:				/* Provide a way for the user to force CHS addressing mode by pressing either Shift key */
+	testb	$0x04, 0x0417	/* I/O memory-mapped keyboard shift flags: 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 */
+	movb	$0x80, %dl		/* change the drive number about to be used in detect_bios_type */
+
+detect_bios_type:
 	/* Check to see if we have EBIOS */
 	pushw	%dx		/* drive number */
 	movb	$0x41, %ah	/* %al == 0 already */
-- 
1.6.0.4