I can't connect WinDbg to target machine over Serial

Hi All,

I've done WinDbg debugging before over Serial. So, this is just messing with my mind at the moment. Hopefully, someone can find my issue with the steps I am using.

On the target machine,
Windows 10 Pro (Build 19041.vb_release.191206-1406)
Using COM2
bcdedit /debug on
bcdedit /dbgsettings serial debugport:2 baudrate:115200

On the Host machine.
Windows 10 Home (Build 19045)
WinDbg from Windows DDK 22621
Using COM4
COM Port: COM4
BAUD: 115200

I've also tried the new WinDbg downloaded from here: https://aka.ms/windbg/download

Neither WinDbg(new) WinDbg(classic) can connect.

Note: I've booted into UEFI shell and sent a character over COM2 to the host machine using COM4. When I use Putty, I can see the character that is transmitted over serial from the target machine on the host machine. So, I know the hardware is setup correctly. Any Ideas on why WinDbg can't connect to the target machine????

Thanks In Advance,

It's a real COM port on the target, yes? Not USB<->Serial or anything.

Hi Scott,

Target Machine = Real COM port.
Host Machine = USB<->Serial.

I had this working before with Visual Studio 2017 with WinDbg classic from DDK = 17763

Are you positive that Windows sees this COM port as COM2? Have you confirmed that you can communicate with Putty from Windows?

It really should "just work", debugger version shouldn't matter.

Hi Scott,

Yes, Windows sees the COM2 port in Device Manager on the Target Machine. That was my feeling as well. It should just work. If I find a resolution on what the issue is, then I will post here.

Hi Ayushmaan,

I was thinking SecureBoot might be the problem. But, that is turned off in the BIOS and I made sure to install the Windows OS on the target machine with this option disabled. Also, I am on a Bare Metal install and not a VM. So, I'm not sure that will fix my problem. But, thank you for the reference as I may use this information in the future when debugging on a VM.