LeapFrog Pollux Platform: FTDI JTAG How To

Background
I had been curious about JTAG ever since I started experimenting with Didj. I had wondered about whether it could be used to investigate our Pollux-based devices.

As we all progressed with our experimentation, Moogle identified the JTAG pads on Didj, and then bcav added a wiki entry on how to use the JTAG port to debug a bootloader on Didj with OpenOCD (Open On-Chip Debugger). We later happily discovered that JTAG pads are clearly labeled on the Leapster Explorer mainboard (in my book, its a Big Win whenever a manufacturer acknowleges our Fundamental Rights!)

I had JTAG experimentation on my list-of-things-to-try for a while, but I didnt want to spend $72 to buy the JTAG dongle bcav used in the wiki entry. (I did have a home-made wiggler cable that I hacked together for use with WRT routers, but I wasn't confident enough that it would fit the bill for this use case. Plus the speed over a parallel port was not great)

Upon learning that that the ftdi2232 chip could be used to bitbang a JTAG connection and that the same part powers many USB-based JTAG cables, I purchased a $30 breakout board that was based on that chip - DLP Design DLP-USB1232H (datasheet).

What follows are the steps I used to make this breakout work with Didj, LX, LPX, and the Pollux-based eGo netbooks.

NOTE: if you aren't interested in wiring up your own usb JTAG using the FT2232, you can purchase a Flyswatter from TinCanTools for $49.95

Connecting


The table below illustrates how to connect the DLP-USB1232H device pins to Didj, LX and the eGo. The pinout on the breakout is in the DLP-USB1232H datasheet (pinout is on page 4 and page 7).

IMPORTANT: You also need to connect pins 8 and 9 together on the DLP-USB1232H module in order to configure it to be powered via USB.

[1] As an alternative to TP103, either side of R43 (jumper/0 Ohms) or the right pad of R45 (unpopulated) works. This is near the other test pads.

Also, the Didj or LX must be powered on.

Software Installation
Install OpenOCD (examples are Ubuntu Lucid)

$ sudo apt-get install openocd

Place this configuration file - name it dlp-usb1232h.cfg - into your openocd /usr/share/openocd/scripts/interface directory:

Place the file below, named openocd.cfg (originally described here), into your home directory:

Usage
To launch OpenOCD from your home directory:

$ sudo /usr/bin/openocd -s /usr/share/openocd/scripts

To access OpenOCD directly, telnet to localhost port 4444:

$ telnet localhost 4444

Usage Examples
Read the registers using the 'mdw phys ' command in OpenOCD. In this example we are reading the MLCCONTROL0 register:

To write registers, use 'mww phys ' In this example we are changing to the MLC to RGB888 mode, setting the H-stride and V-stride appropriately, and then setting the dirty flag:

The reset command will restart the device: >reset To debug bootloaders with GDB, see Didj JTAG How To.

Resources
The DLP-USB1232H is available from various sources, e.g.: Digikey, Mouser, or Saelig.

The module can also be used as a cheap and simple SPI BIOS chip programmer together with the flashrom utility.