Duplicate COM ports

[gus.quiroga]

We are seeing duplicate COM port assignments in Device
Manager. That is, there are sometimes 2 COM1s or 2 COM2s
or sometimes the correct configuration which is a COM1 and
COM2. A discussion with MS Tech Support revealed that the
HKLM\SYSTEM\CurrentControlSet\Enum\Root\*PNP0501 registry
key was not as it should be which is either the hardware
or the PnP misbehaving or somebody stepping on the
exchange. We are pounding on all fronts including the
motherboard and BIOS manufacturers but I thought it would
be worth a shot to see if anybody else has experienced
this.

 

[SaltPeter]

We are seeing duplicate COM port assignments in Device
Manager. That is, there are sometimes 2 COM1s or 2 COM2s
or sometimes the correct configuration which is a COM1 and
COM2. A discussion with MS Tech Support revealed that the
HKLM\SYSTEM\CurrentControlSet\Enum\Root\*PNP0501 registry
key was not as it should be which is either the hardware
or the PnP misbehaving or somebody stepping on the
exchange. We are pounding on all fronts including the
motherboard and BIOS manufacturers but I thought it would
be worth a shot to see if anybody else has experienced
this.

You never mentioned if W2K is running a standard HAL or ACPI HAL.

Sounds like an ACPI issue to me. When run using an ACPI HAL, as opposed to a
standard HAL, W2K creates a virtual IRQ table to reroute hardware resources.

Imagine an ACPI compatible motherboard thats running an ACPI W2K OS
installation. Some bioses provide the ability to disable ACPI support. All
of a sudden, W2K reroutes resources using the virtual table but the board
supplies a concurrent non-ACPI interface to its com ports as well. Hence:
the duplicates.

Try updating the motherboard's bios, then check for any ACPI option it might
provide. I'ld suggest using Pause to freeze POST (ESC to release) during
mobo's hardware detection and hardware configuration to confirm assigned
resources before W2K re-assigns them, if at all.

Finally, any IRDA ports enabled?

 

[Gus]

We are using a Standard HAL. The BIOS (believe it or not)
does not have a disable-ACPI capability. Instead it has a
disable-APM capability (ancient times). Yet the BIOS is a
custom built BIOS that was made for us earlier this year.
So, W2K correctly finds a Standard PC underneath it during
its installation and the BIOS is not ACPI, yet we are
still seeing the duplicate ports.

It could still be correct in that the BIOS sets up one
configuration and W2K another and we get a mish-mash. In
particular the
HKLM\System\CurrentControlSet\Root\Enum\*pnp0501 key ends
up with 3 entries underneath it even though there are only
2 COM ports. One of the entries is alway incomplete
(missing a key) so the device mgr ends up using the
complete ones (ones that have all 3 keys) to build the
device tree and sometimes the complete ones are both COM2s
and other times both COM1s and sometimes COM1 and COM2.

I have a question into the BIOS manufacturers to see if
the custom BIOS they built is a PnP BIOS. Given that it
still has an APM setting it might just be old enough to be
a non-PnP BIOS.

Any other thoughts given the new information?

- Gus

 

[SaltPeter]

We are using a Standard HAL. The BIOS (believe it or not)
does not have a disable-ACPI capability. Instead it has a
disable-APM capability (ancient times). Yet the BIOS is a
custom built BIOS that was made for us earlier this year.
So, W2K correctly finds a Standard PC underneath it during
its installation and the BIOS is not ACPI, yet we are
still seeing the duplicate ports.

It could still be correct in that the BIOS sets up one
configuration and W2K another and we get a mish-mash. In
particular the
HKLM\System\CurrentControlSet\Root\Enum\*pnp0501 key ends
up with 3 entries underneath it even though there are only
2 COM ports. One of the entries is alway incomplete
(missing a key) so the device mgr ends up using the
complete ones (ones that have all 3 keys) to build the
device tree and sometimes the complete ones are both COM2s
and other times both COM1s and sometimes COM1 and COM2.

I have a question into the BIOS manufacturers to see if
the custom BIOS they built is a PnP BIOS. Given that it
still has an APM setting it might just be old enough to be
a non-PnP BIOS.

Any other thoughts given the new information?

Nothing new, have you tried disabling the com ports? Assuming they aren't
needed.

Did you verify POST's device initialistion resource list? Its displayed
during a cold boot usually. Perhaps its the motherboard thats providing
duplicate com ports.

Since its a standard Hal, try slowing POST down a little. Sounds crazy? its
not. Most bioses provide a POST bios speed control mechanism which is
controlled via keyboard. Depending on bios and during POST, CTRL + or + and
CTRL - or - speeds up and slows POST execution. Tried clearing NVRAM? As in
clear CMOS?