I'm using an Arduino Due board and a Black Magic probe v2.3b. Both "start" and "attach to process" methods do not work, but "attach to process" seems like it's close to working.

The BMP is running SW v1.9.0-rc0, HW revision 6. I am able to connect to it and attach to the Due through the command line using the commands:
"target extended-remote //./COM9"
"monitor swdp_scan"
[displays the Due]
"attach 1"
And I've been able to manually load the program's .elf to the debugger and attach to the Due that way.

In the Debug output (shown in the attached .txt file) it lists off several GDB commands. I've interacted with GDB through the command line (the same arm-none-eabi-gdb.exe Visual Micro uses), and I didn't run into any problems when I tried the same commands. COM9 is the correct port.

When I start debugging using "Start", it either displays the same thing as "Attach to process" (see .txt) or it says something like "debugging is not configured for this build" (it is, and it's a tossup as to which message it displays). "Attach to process" consistently shows what is seen in the .txt. 

This is when the optimization is set to "default optimizations" and the optimizations are disabled in the project's properties (Project -> Project Properties -> Configuration Properties -> C/C++ -> Optimization). 

"No optimizations" doesn't compile and gives me the error:
"core.a(UARTClass.cpp.o)*: In function HardwareSerial::HardwareSerial()
HardwareSerial.h:26: undefined reference to vtable for HardwareSerial"
The "No project" and "No project + libraries" optimization modes compiler, but they cause a popup box that says the same thing, regardless of if I try using "Start" or "Attach to process": 
"Unable to start debugging. Unexpected GDB output from command "-exec-run". Don't know how to run. Try "help target". 

I made sure to clean the solution when changing optimization levels. I've also tried every combination of restarting the Due and the black magic probe and starting them up in different orders.

I wanted to try everything I could before asking for help so I wouldn't waste anyone's time, but I'm stumped. Let me know if I missed anything.

I'm using Visual Micro Version 2.2022.1128, version minor 25 (the latest as of 18 Jan 2023). Windows 11 22H2 build 22621.1105. Visual Studio 2022 version 17.4.4. Using Arduino 2.

Thanks for the reply, but I'm still getting the same problem. I tried the shorter list of commands and that didn't change the output (but I did notice it was using the shorter set of commands that you attached). The commands work fine outside of Visual Studio/micro, and I mainly brought that up to show that my debugger is functional.

"Attach to process" does not work as it should. Check the text file attached to my original post for the output. I made sure there were no stray gdb processes running.

I've been messing around with it to try to figure anything out. I was able to load the .elf to the probe and view variables and functions by name via command line (one command at a time), but I had no way of controlling the program, so it wasn't very helpful. The breakpoints set in Visual Studio don't do anything and including them does not change the output file, which I confirmed by comparing hashes.

The only things I found that might be helpful is that the "start" command returns "Can't kill process" and then causes the probe to disconnect, and breakpoints (using the BKPT <imm8> instruction) cause the Due to hard fault, which I can tell by the PSR. Whether or not it's relevant, that's all I got.

Thanks again, for all the info and the help. I'm new to debuggers and I couldn't do this without help. 

I forgot to try rolling back the firmware, but I got around to it today. The probe I'm using is v2.3b, which got supported in 1.8.0. I didn't realize it until after I flashed 1.7.1, which caused it to not respond when attached to the board. The latest stables are 1.8.0 and 1.8.2.

I've tried a few different firmware versions. I made a fresh project with an unmodified board.txt when testing these. All loaded with DFU-util:
1.7.1 - Doesn't work
1.8.0/1.8.2 - Fails in VS, iffy in CMD. They behave the same, and I've attached the output from "Attach to process". The error is different than the one I posted when I was on 1.9.0rc0. I want to add that, when interfacing with it via CLI, the probe had a 50/50 chance as to whether or not it was able to find the board with "monitor swdp_scan", or just outright freeze at "Target voltage 3.3v".
1.9.0-rc1 - Fails in VS, almost working in CMD. Similar result to 1.9.0-rc0. Output file attached. This firmware works well in the command line, more of the functions/commands work, it's very consistent, the only problem I'm having over CLI is I cannot add breakpoints. When I try to add a breakpoint to setup/main/loop I get this error, even after I deleted all breakpoints (and it shows no breakpoints):

"Warning:
Cannot insert hardware breakpoint [number].
Could not insert hardware breakpoints:
You may have requested too many hardware breakpoints/watchpoints."

I couldn't even get that far in 1.9.0rc0, for what it's worth. I'd like the convenience of debugging in VS if possible, but for the project I'm working on right now, just getting it set up in CLI would be huge.

I bought my board off of Adafruit's website. Here's the store link I used:
https://www.adafruit.com/product/3839

I'm going to test my ribbon cable connections later today, and I think I can get access to another PC, to see if it's something with my computer.