Put a ribbon on it... we finally got working A20M code. This should besyslinux-1.40

the official 1.40.

2 files changed, 70 insertions, 52 deletions

diff --git a/NEWS b/NEWS
index 839815a1..712272fb 100644
--- a/NEWS
+++ b/NEWS
@@ -1,7 +1,7 @@
 Changes in 1.40:
-	* Increase A20M delay to avoid problems on certain IBM
-	  Thinkpads (thanks to Donnie Barnes of RedHat for vital info
-	  on this one.)
+	* Increase A20M delay and put in a test to avoid problems on
+	  certain IBM Thinkpads (thanks to Donnie Barnes of RedHat
+	  for vital info on this one.)
 	* Support COMBOOT style boot command images.
 	* Support chain loading (foreign operating systems, e.g. DOS).
 	* Include a new "copybs" DOS utility to copy a boot sector to
@@ -58,45 +58,45 @@ Changes in 1.31:
 	  don't need Turbo C.)
 
 Changes in 1.30:
-        * Added support for loading bzImage and initrd loading, and made
-          SYSLINUX new-setup-code aware (SYSLINUX 1.30 id=0x31).
-        * Added LILO-style kernel labels; see the LABEL and IMPLICIT
-          keywords in README file.
-        * Added support for colorization of intro and help screens.
-        * The vga= option is now handled correctly.
-        * Massive rewrite of large chunks of the code in order to
-          support the first two new features.
+	* Added support for loading bzImage and initrd loading, and made
+	  SYSLINUX new-setup-code aware (SYSLINUX 1.30 id=0x31).
+	* Added LILO-style kernel labels; see the LABEL and IMPLICIT
+	  keywords in README file.
+	* Added support for colorization of intro and help screens.
+	* The vga= option is now handled correctly.
+	* Massive rewrite of large chunks of the code in order to
+	  support the first two new features.
 
 Changes in 1.20:
-        * Added simple online help at the "boot:" prompt.
-        * Removed 2880K image as I no longer have access to such a
-          floppy drive.  (Donations accepted!!)
-        * Decided to distribute the source in a subdirectory rather
-          than in a nested zipfile.
+	* Added simple online help at the "boot:" prompt.
+	* Removed 2880K image as I no longer have access to such a
+	  floppy drive.	 (Donations accepted!!)
+	* Decided to distribute the source in a subdirectory rather
+	  than in a nested zipfile.
 
 Changes in 1.11:
-        * Removed a sanity check which would cause booting to fail on
-          Phoenix BIOS version 4.03.  Apparently this BIOS is buggy.
+	* Removed a sanity check which would cause booting to fail on
+	  Phoenix BIOS version 4.03.  Apparently this BIOS is buggy.
 
 Changes in 1.10:
-        * Added configuration file SYSLINUX.CFG.  This file contains all
-          configurable options, and can be edited from any OS which can
-          access an MS-DOS filesystem; there is no longer a need to run
-          SYSLINUX.EXE except to write the boot sector.
-        * Default command line now given by "default" line in config
-          file.
-        * LINUXMSG.TXT and BOOTMSG.TXT hard-coded file names replaced by
-          "display" and "prompt" lines in config file.
-        * LILO-style option appending now supported ("append" line in
-          config file).
-        * Prompt timeout is now supported ("timeout" line in config
-          file).  The timeout is cancelled when anything is typed on the
-          command line.
-        * Pressing <ESC> or <Ctrl-C> at the Loading... stage now aborts
-          the kernel loading in progress and returns the user to the
-          boot: prompt.
-        * The installer now automatically sets the READONLY flag on
-          LDLINUX.SYS.
+	* Added configuration file SYSLINUX.CFG.  This file contains all
+	  configurable options, and can be edited from any OS which can
+	  access an MS-DOS filesystem; there is no longer a need to run
+	  SYSLINUX.EXE except to write the boot sector.
+	* Default command line now given by "default" line in config
+	  file.
+	* LINUXMSG.TXT and BOOTMSG.TXT hard-coded file names replaced by
+	  "display" and "prompt" lines in config file.
+	* LILO-style option appending now supported ("append" line in
+	  config file).
+	* Prompt timeout is now supported ("timeout" line in config
+	  file).  The timeout is cancelled when anything is typed on the
+	  command line.
+	* Pressing <ESC> or <Ctrl-C> at the Loading... stage now aborts
+	  the kernel loading in progress and returns the user to the
+	  boot: prompt.
+	* The installer now automatically sets the READONLY flag on
+	  LDLINUX.SYS.
 	* Added 2880K disk image.
 
 Changes in 1.03:
@@ -107,13 +107,13 @@ Changes in 1.03:
 	* Changed default kernel name on disk images to LINUX.
 
 Changes in 1.02:
-        * Fixed bug that would garble the command line on recent kernels
-          with more than 4 sectors of setup code (this wasn't really a
-          *bug*; rather, a kernel change broke the code.  Unfortunately
-          the Linux boot interface is still sorely undocumented).
-        * Added BOOTMSG.TXT file support (message file which does not
-          force display of the boot prompt).
+	* Fixed bug that would garble the command line on recent kernels
+	  with more than 4 sectors of setup code (this wasn't really a
+	  *bug*; rather, a kernel change broke the code.  Unfortunately
+	  the Linux boot interface is still sorely undocumented).
+	* Added BOOTMSG.TXT file support (message file which does not
+	  force display of the boot prompt).
 
 Changes in 1.01:
-        * Fixed bug on some (most?) 386 BIOSes would require two boot
-          attempts.
+	* Fixed bug on some (most?) 386 BIOSes would require two boot
+	  attempts.
diff --git a/ldlinux.asm b/ldlinux.asm
index c15e9b19..9185bec2 100644
--- a/ldlinux.asm
+++ b/ldlinux.asm
@@ -341,6 +341,7 @@ InitRDCNameLen  resw 1			; Length of unmangled initrd name
 NextCharJump    resw 1			; Routine to interpret next print char
 SetupSecs	resw 1			; Number of setup sectors
 SavedSP		resw 1			; Our SP while running a COMBOOT image
+A20test		resw 1			; Counter for testing status of A20
 TextAttrBX      equ $
 TextAttribute   resb 1			; Text attribute for message file
 TextPage        resb 1			; Active display page
@@ -2300,8 +2301,8 @@ bcopy:
 ;
 ; We typically toggle A20 twice for every 64K transferred.
 ; 
-%define	io_delay  out 080h,al		; Invalid port (we hope)
-%define delaytime 1024			; ISA bus cycles (1.5 µs)
+%define	io_delay  times 4 out 0EDh,al	; Invalid port (we hope)
+%define delaytime 256			; 4 x ISA bus cycles (@ 1.5 µs)
 
 enable_a20:
 		call empty_8042
@@ -2310,12 +2311,21 @@ enable_a20:
 		call empty_8042
 		mov al,0DFh		; A20 on
 		out 060h, al
-kbc_delay:	call empty_8042
-		push cx
-		mov cx, delaytime
-.delayloop:	io_delay
-		loop .delayloop
-		pop cx
+		call kbc_delay
+		; 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
+		; we don't do the same check in the disable case, because
+		; we don't want to *require* A20 masking (SYSLINUX should
+		; work fine without it, if the BIOS does.)
+		push es
+		mov ax,0FFFFh		; HMA
+		mov es,ax
+.a20_wait:	inc word [ss:A20test]
+		mov ax,[es:A20test+10h]
+		cmp ax,[ss:A20test]
+		je .a20_wait
+		pop es
 		ret
 
 disable_a20:
@@ -2327,6 +2337,14 @@ disable_a20:
 		out 060h, al
 		jmp short kbc_delay
 
+kbc_delay:	call empty_8042
+		push cx
+		mov cx, delaytime
+.delayloop:	io_delay
+		loop .delayloop
+		pop cx
+		ret
+
 empty_8042:
 		io_delay
 		in al, 064h		; Status port