Just wanted to circle back on this, to provide some updates. Got my legit csync cable from retrogamingcables, and moved csync_o back to pin 3. This SNES is now looking and capturing as gloriously as ever.
I also wanted to provide the pre-configured pi image, in case anyone would find it useful for their dejitter board assembly/programming project.
Tested on Pi 1 Model B+, Pi 2, Pi 3 Model B; and snes_dejiter v1.2. The complete assembled and programmed dejitter board tested on SNES Mini (SNN-CPU-01).
Download pi image here: https://drive.google.com/open?id=1iy0jj0sSLmQe0vSsW8BpHByIsduTYyF9
There is a gui version and a non-gui version. The non-gui version may fit on a 2GB SD card, but I would go with a 4GB minimum, for either image, to be safe.
Connect 5V and ground from GPIO header to dejitter board JTAG connector before power on pi. Hot-plugging the JTAG signal lines is no problem, but hot-plugging 5V may cause a voltage error, requiring the pi to rebooted.
As far as I can tell, GPIO implementation on the Pi has not changed over the various model revisions, with the exception of the base address being different on Pi 3, compared to its predecessors. /home/pi/openocd-pi.conf contains instructions for changing the base address within the file, to ensure compatibility. Openocd-pi.conf contains much useful information, including GPIO header pin assignments, for connecting to dejitter board for programming:
>sudo nano /home/pi/openocd-pi.conf
Once you have read through openocd-pi.conf and done any initial testing, connect dejitter board to GPIO header/pi, and run the following commands:
> cd /home/pi
> sudo openocd –f openocd-pi.conf
Then proceed with the following instructions from marqs’ readme:
3. OpenOCD auto-probing should report a TAP controller with id 0x0150203f. You can now open another terminal to interact with openocd and program the chip:
telnet localhost 4444
> svf /home/pi/snes_dejitter.svf
4. The programming procedure should finish with no error, after which you can finish installation by powering off hardware and disconnecting the programmer.
/home/pi also contains snes_dejitter_new.svf, which is the latest svf version contained at the project github page. Programming with this svf was not successful for me, and I suggest ignoring this svf file, but it is there for posterity.
:edit: The uploaded image and dejitter board programming has now been tested successfully with a Pi (1) Model B+ and Pi 3 Model B (gpio base address has to be changed in /home/pi/openocd-pi.conf; notes are included within openocd-pi.conf, if you open it in a text editor).