While dragging all my old hardware out of the loft, I camme across an original GPH breakout board, and also a cradle. Both have a built in 'wiggler' JTAG parallel port adapter and while I do still have a parallel port on my desktop, I never found it to be particularly reliable in the past so would rather use my Olimex USB JTAG dongle. Furthermore, I'd like to experiment with connecting some ESP8266 boards to the UART pins directly, without the level shifting on the RS232 connections provided by the GPH boards.
To this end, I set about constructing my own using the connectors which can be purchased at multi-com.pl. I got some 24-core signal cable used to wire in burglar alarms, and built a cable terminating in a DB25 connector, so I can use it for multiple boards (e.g. Wiz, Caanoo) in the future.
I have prepared a schematic based on the information on the GP2X Wiki, and created a board layout in EasyEDA. It cost $2 for 5 boards including delivery from jlcpcp.com (which is the same company as EasyEDA, so has good integration with the layout tool).
Using a cheap CLP2102 based UART<->USB serial dongle off eBay, I have successfully got the serial console working, use baud rate 115200 and 8N1 settings in Minicom.
For JTAG, you can download my example openocd 0.10.0 config here. To connect to the GP2X, run:
openocd -f gp2x-openocd.cfgYou'll need to tweak the interface part of the file for whatever JTAG interface you will be using. A simple way to test if it is working is to telnet localhost 4444 then issue the following command which displays the content of the GPIO register the buttons are connected to:
mdh phys 0xc0001184 1
I've always found the F100 has really unreliable JTAG, it is worse for MK2 units (those with a Korean label on the back) on which I have almost never managed to initiate a stable connection (I suspect this may be due to the nRESET pin being removed in the MK2). My First Edition unit works fine, as does my F200.