A20 gate not responding! error message

[Claus Futtrup]

Dear all,

Please give any hints to solving the above error message. I have tried first
to install Coyote Linux on a floppy to boot on the old machine, then
Floppyfw ... both give the same error:

Loading initrd.gz...
A20 gate not responding!
boot: _

I am a newbie to Linux. I understand the message the way that Linux is
waiting for me to put an acceptable boot disk in the floppy drive.

The Floppydisk for Floppyfw is made with rawwritewin.exe - without any error
messages and with floppyfw-current.img.

I hope one of you guys can get me started solving this (in the right
direction). As a newbie I will probably need a good explanation.

I have searched the web and become a quite a bit more knowledgeable about
this, but no solution showed up (in a way that I can understand).
http://www.win.tue.nl/~aeb/linux/kbd/A20.html
(from
http://www.telenovela-world.com/~spade/linux/howto/Linux-i386-Boot-Code-HOWTO/setup.html#enable_a20)

The way I understand it - hardware is a multitude of possibilities and the
solution depends on my hardware. Therefore this short description:

PC/AT 486DX/33, mainboard from UMC, UM486, which is based on the UM82C480
chipset (consisting of UM82C481 = memory controller, UM82C482 = system
controller og UM82C206 = peripheral controller).

The boeard is equipped with 128 kb cache (one bank out of two : 4 x 32 kb
SRAM), and 20 Mb 30-Pin DRAM configured as 4 x 1Mb in bank 0 + 4 x 4Mb in
bank
1. The RAM is with true parity bit (it is old server hardware) - not ASIC
"cheating-parity."

The board is too old to have VESA local bus, it only has 8-bit XT ISA, and
16-bit AT ISA slots.

In the manual it says:
Support fast A20 Gate and fast CPU reset to boost performance of software
utilizing 80486 protected mode, such as OS/2, UNIX,...etc.

Besides it says under potential fatal errors:
8042 GATE-A20 ERROR: error in getting into protected mode.
My BIOS doesn't give this error, so I assume that A20 works as it should. I
can see that 8042 is some hardware for keyboard control sitting right next
to the BIOS.

BIOS:
BIOS-Version: UM486/486SX V1.3 09-24-91
BIOS-Date: 07/07/91
BIOS-ID string: 40-0500-D01131-00101111-070791-UMCWB-F

This BIOS has no settings named anything like A20. The BIOS cannot be
updated (it isnot a flash BIOS).

In the setup of the BIOS the machine is running without any fiddling with
parameters.
(regular clock / 4 on the bus, no fast page DRAM + 2 ms wait state which is
how it should be)

What can I do to move on?

Best regards,
Claus

[KR]

Post by Claus Futtrup
Please give any hints to solving the above error message. I have tried first
to install Coyote Linux on a floppy to boot on the old machine, then
Loading initrd.gz...
A20 gate not responding!
boot: _

The motherboard is probably broken.

The A20 line is activated and deactivated by (wait for it) the keyboard
controller. You could try replacing it with a 8042 IC from another board.

[Claus Futtrup]

Hi Kristian and all,

Post by KR

Post by Claus Futtrup
Loading initrd.gz...
A20 gate not responding!
boot: _

The motherboard is probably broken.
The A20 line is activated and deactivated by (wait for it) the keyboard
controller. You could try replacing it with a 8042 IC from another board.
8042 GATE-A20 ERROR: error in getting into protected mode.
My BIOS doesn't give this error, so I assume that A20 works as it should.

Best regards,
Claus

[Jules]

Post by Claus Futtrup
Hi Kristian and all,

Post by KR

Post by Claus Futtrup
Loading initrd.gz...
A20 gate not responding!
boot: _

The motherboard is probably broken.
The A20 line is activated and deactivated by (wait for it) the keyboard
controller. You could try replacing it with a 8042 IC from another board.
8042 GATE-A20 ERROR: error in getting into protected mode.
My BIOS doesn't give this error, so I assume that A20 works as it should.

Far as I know a PC BIOS code will only ever be running in real mode
though; the jump to protected mode will only happen when the Linux
kernel's loaded (or the equivalent under Windows, say).

I'm sure very old PC BIOSes used to test the A20 line at machine startup
though - but maybe they no longer bother doing this in order to save ROM
space for other things.

[Larry Blanchard]

Post by Jules
I'm sure very old PC BIOSes used to test the A20 line at machine startup
though - but maybe they no longer bother doing this in order to save ROM
space for other things.

IIRC, some PC Bioses will let you enable/disable that line. Perhaps the
OP should check that.

[Claus Futtrup]

Hi Jules, Larry and al

Post by Larry Blanchard

Post by Jules
I'm sure very old PC BIOSes used to test the A20 line at machine startup
though - but maybe they no longer bother doing this in order to save ROM
space for other things.

IIRC, some PC Bioses will let you enable/disable that line. Perhaps the
OP should check that.

Thank you for your concern about this issue. The AMI BIOS has the following
options (I don't see anything that will tinker with the A20 - or the 8042
keyboard controller):

Standard CMOS Setup
Simple stuff, like time and date, HD and FD setup, VGA and Keyboard.

Advanced CMOS Setup
* Above 1Mb Mem Test - disabled
* HD RAM Area - 0:300
* Sys Boot w. Num Lock - ON
* Weitek (math-) Processor - disabled
* Cache Memory - Both
* Password Checking - disabled
* VROM Shadow C000 - Yes
* VROM Shadow C400 - Yes
* VROM Shadow F000 - Yes
* Main Memory relocation - Yes

Advanced Chipset Setup
* Bus Clock - CLKIN / 4
* Fast Page Mode DRAM - disabled
* DRAM Wait States - 2 W/S
* Non Cache Mem - disabled
* Non Cache Mem - disabled
* Non Cache Mem - disabled
* Non Cache Mem - disabled
Mem above 16Mb cacheable - disabled
F000 Mem, 64k cacheabel - Yes
C000 Mem, 16k cacheabel - Yes
C400 Mem, 16k cacheabel - Yes

If you can pin the problem, then it is highly appreciated.

Best regards,
Claus

[r***@yahoo.com]

Real mode can only access the lower 1 MB, so the BIOS has to switch to
protected mode for the memory test.
I would guess Claus's problem is caused by a mobo incompatibility.
Maybe GateA20 switches too slowly or it supports *only* Fast GateA20
(which is an IO port external to the 8042.)
This could be influenced by peripherals connected to the KBC. Try
another keyboard/mouse or disconnect them all. But otherwise this looks
like a problem that needs motherboard schematics and kernel source
work.

[Beowulf]

Post by Claus Futtrup
Dear all,
Please give any hints to solving the above error message. I have tried first
to install Coyote Linux on a floppy to boot on the old machine, then
Loading initrd.gz...
A20 gate not responding!
boot: _
I am a newbie to Linux. I understand the message the way that Linux is
waiting for me to put an acceptable boot disk in the floppy drive.
The Floppydisk for Floppyfw is made with rawwritewin.exe - without any error
messages and with floppyfw-current.img.
I hope one of you guys can get me started solving this (in the right
direction). As a newbie I will probably need a good explanation.
I have searched the web and become a quite a bit more knowledgeable about
this, but no solution showed up (in a way that I can understand).
http://www.win.tue.nl/~aeb/linux/kbd/A20.html
(from
http://www.telenovela-world.com/~spade/linux/howto/Linux-i386-Boot-Code-HOWTO/setup.html#enable_a20)
The way I understand it - hardware is a multitude of possibilities and the
PC/AT 486DX/33, mainboard from UMC, UM486, which is based on the UM82C480
chipset (consisting of UM82C481 = memory controller, UM82C482 = system
controller og UM82C206 = peripheral controller).
The boeard is equipped with 128 kb cache (one bank out of two : 4 x 32 kb
SRAM), and 20 Mb 30-Pin DRAM configured as 4 x 1Mb in bank 0 + 4 x 4Mb in
bank
1. The RAM is with true parity bit (it is old server hardware) - not ASIC
"cheating-parity."
The board is too old to have VESA local bus, it only has 8-bit XT ISA, and
16-bit AT ISA slots.
Support fast A20 Gate and fast CPU reset to boost performance of software
utilizing 80486 protected mode, such as OS/2, UNIX,...etc.
8042 GATE-A20 ERROR: error in getting into protected mode.
My BIOS doesn't give this error, so I assume that A20 works as it should. I
can see that 8042 is some hardware for keyboard control sitting right next
to the BIOS.
BIOS-Version: UM486/486SX V1.3 09-24-91
BIOS-Date: 07/07/91
BIOS-ID string: 40-0500-D01131-00101111-070791-UMCWB-F
This BIOS has no settings named anything like A20. The BIOS cannot be
updated (it isnot a flash BIOS).
In the setup of the BIOS the machine is running without any fiddling with
parameters.
(regular clock / 4 on the bus, no fast page DRAM + 2 ms wait state which is
how it should be)
What can I do to move on?
Best regards,
Claus

1. BIOS runs in real mode
2. bad keyboard and/or mouse port

Are you using a PS/2 mouse port? I've seen this behavior with the early
PS/2 implementations since the UART is shared with the keyboard.

The A20 line is required to go into protected mode and NEEDS the proper
keyboard (thank IBM!). If you can't go to protected mode then the
keyboard or UART on the motherboard is the culprit. Many newer kb don't
supply the correct A20 line.

This is a well known "old school" issue that popped up alot with windows
3.1 and os/2 back in the day.

[Claus Futtrup]

Post by Beowulf
1. BIOS runs in real mode
2. bad keyboard and/or mouse port
Are you using a PS/2 mouse port? I've seen this behavior with the early
PS/2 implementations since the UART is shared with the keyboard.

No, the mouse runs on COM1. The Keyboard is not PS/2 either - this is so
old, that it uses an AT keyboard (5-pin DIN socket).

Post by Beowulf
The A20 line is required to go into protected mode and NEEDS the proper
keyboard (thank IBM!). If you can't go to protected mode then the
keyboard or UART on the motherboard is the culprit. Many newer kb don't
supply the correct A20 line.

Thanks for this explanation. This sounds tricky.

Post by Beowulf
This is a well known "old school" issue that popped up alot with windows
3.1 and os/2 back in the day.

Yes ... and the computer runs Win 3.11 just fine (and used to run OS/2 just
fine as well). This is what makes me think there is something sneaky about
it - perhaps Linux just doesn't support the hardware anymore.

Best regards,
Claus

[Beowulf]

Post by Claus Futtrup

Post by Beowulf
1. BIOS runs in real mode
2. bad keyboard and/or mouse port
Are you using a PS/2 mouse port? I've seen this behavior with the early
PS/2 implementations since the UART is shared with the keyboard.

No, the mouse runs on COM1. The Keyboard is not PS/2 either - this is so
old, that it uses an AT keyboard (5-pin DIN socket).

Post by Beowulf
The A20 line is required to go into protected mode and NEEDS the proper
keyboard (thank IBM!). If you can't go to protected mode then the
keyboard or UART on the motherboard is the culprit. Many newer kb don't
supply the correct A20 line.

Thanks for this explanation. This sounds tricky.

Post by Beowulf
This is a well known "old school" issue that popped up alot with windows
3.1 and os/2 back in the day.

Yes ... and the computer runs Win 3.11 just fine (and used to run OS/2 just
fine as well). This is what makes me think there is something sneaky about
it - perhaps Linux just doesn't support the hardware anymore.
Best regards,
Claus

Say, You may want to try slackware. I've had good luck with it on older
hw. Although I haven't gone THAT far back with it! It may be that
Coyote isn't properly recognizing the chipset but that Slack will. I
did run it on on old AMD486DX100 with SIS chipset (slack v. 7)