I connect to the board by putty and run the following:
gdbserver --multi :2345
And I get:
Listening on port 2345
Then I run the following in Windows cmd (on the PC that the board is connected to via serial port):
(gdb) target extended :2345
And after a few seconds, I get:
:2345: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
I also tried COM17:2345 instead of just :2345 and I got:
COM17:2345: No such file or directory.
(COM17 is the serial port I'm connected to as it appears in Device Manager)