From: H. Peter Anvin <hpa@zytor.com>
Date: Wed, 18 Jun 2008 16:05:33 +0000 (-0700)
Subject: TEST: issue a null command to the KBC as part of A20-flipping
X-Git-Tag: syslinux-3.70-pre19^0
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=34ffe9a0423644b7635683e462cab573f97ff255;p=platform%2Fupstream%2Fsyslinux.git

TEST: issue a null command to the KBC as part of A20-flipping

UHCI supposedly wants a null command (0FFh) sent to the KBC as part of
the A20-flipping sequence.  See if that works for us.
---

diff --git a/core/bcopy32.inc b/core/bcopy32.inc
index 8f36d64..4ebbe3c 100644
--- a/core/bcopy32.inc
+++ b/core/bcopy32.inc
@@ -413,7 +413,7 @@ a20_kbc:
 
 		mov byte [cs:A20Type], A20_KBC	; Starting KBC command sequence
 
-		mov al,0D1h			; Command write
+		mov al,0D1h			; Write output port
 		out 064h, al
 		call empty_8042_uncond
 
@@ -421,6 +421,13 @@ a20_kbc:
 		out 060h, al
 		call empty_8042_uncond
 
+		; Apparently the UHCI spec assumes that A20 toggle
+		; ends with a null command (assumed to be for sychronization?)
+		; Put it here to see if it helps anything...
+		mov al,0FFh			; Null command
+		out 064h, al
+		call empty_8042_uncond
+
 		; Verify that A20 actually is enabled.  Do that by
 		; observing a word in low memory and the same word in
 		; the HMA until they are no longer coherent.  Note that
@@ -534,12 +541,19 @@ a20d_fast:
 ;
 a20d_kbc:
 		call empty_8042_uncond
+
 		mov al,0D1h
-		out 064h, al		; Command write
+		out 064h, al		; Write output port
 		call empty_8042_uncond
+
 		mov al,0DDh		; A20 off
 		out 060h, al
 		call empty_8042_uncond
+
+		mov al,0FFh		; Null command/synchronization
+		out 064h, al
+		call empty_8042_uncond
+
 		; Wait a bit for it to take effect
 a20d_snooze:
 		push cx
diff --git a/memdisk/memdisk16.asm b/memdisk/memdisk16.asm
index 692ed8b..d73ddc5 100644
--- a/memdisk/memdisk16.asm
+++ b/memdisk/memdisk16.asm
@@ -294,7 +294,7 @@ a20_kbc:
 
 		mov byte [A20Type], A20_KBC	; Starting KBC command sequence
 
-		mov al,0D1h			; Command write
+		mov al,0D1h			; Write output port
 		out 064h, al
 		call empty_8042_uncond
 
@@ -302,6 +302,13 @@ a20_kbc:
 		out 060h, al
 		call empty_8042_uncond
 
+		; Apparently the UHCI spec assumes that A20 toggle
+		; ends with a null command (assumed to be for sychronization?)
+		; Put it here to see if it helps anything...
+		mov al,0FFh			; Null command
+		out 064h, al
+		call empty_8042_uncond
+
 		; Verify that A20 actually is enabled.  Do that by
 		; observing a word in low memory and the same word in
 		; the HMA until they are no longer coherent.  Note that
@@ -424,12 +431,19 @@ a20d_fast:
 ;
 a20d_kbc:
 		call empty_8042_uncond
+
 		mov al,0D1h
-		out 064h, al		; Command write
+		out 064h, al		; Write output port
 		call empty_8042_uncond
+
 		mov al,0DDh		; A20 off
 		out 060h, al
 		call empty_8042_uncond
+
+		mov al,0FFh		; Null command/synchronization
+		out 064h, al
+		call empty_8042_uncond
+
 		; Wait a bit for it to take effect
 a20d_snooze:
 		push cx