LeapFrog Pollux Platform: FTDI JTAG How To

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Didj FTDI2232 JTAG setup


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 and LX.


Didj JTAG pads
Didj nSRST pad on opposite side of mainboard from JTAG pads
Explorer JTAG pads
Augen eGo 730-4 front JTAG pads
Augen eGo 730-4 back JTAG pads

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

Pin type DLP-USB1232H pin # Didj Test Pad label LX Test Pad label
(S)RST 13 TP103 nRST
GND Either 1 or 10 TP14 GND

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.

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/interfaces directory:

# DLP Design DLP-USB1232H USB-to-UART/FIFO interface module
# http://www.dlpdesign.com/usb/usb1232h.shtml
interface ft2232
ft2232_device_desc "Dual RS232-HS"
ft2232_layout usbjtag
ft2232_vid_pid 0x0403 0x6010

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

telnet port 4444
source [find interface/dlp-usb1232h.cfg]
jtag_khz 15000
# length of reset signal: [ms]
jtag_nsrst_assert_width 100
# don't talk to JTAG after reset for: [ms]
jtag_nsrst_delay 250
reset_config trst_and_srst separate
# end reset config
if { [info exists CHIPNAME] } {
} else {
  set  _CHIPNAME pollux
if { [info exists ENDIAN] } {
} else {
  set  _ENDIAN little
if { [info exists CPUTAPID ] } {
} else {
  # force an error till we get a good number
  set _CPUTAPID 0x07926f0f
#jtag scan chain
jtag newtap $_CHIPNAME cpu -irlen 4 -expected-id $_CPUTAPID
target create $_TARGETNAME arm926ejs -endian $_ENDIAN -chain-position $_TARGETNAME -variant arm926ejs 


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 <address>' command in OpenOCD. In this example we are reading the MLCCONTROL0 register:

>mdw phys 0xc0004024
0xc0004024: 86534024

To write registers, use 'mww phys <address> <value>' 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:

>mww phys 0xc0004024 0x46534024
>mww phys 0xc0004028 0x00000003
>mww phys 0xc000402c 0x000003c0
>mww phys 0xc0004024 0x4653d034

The reset command will restart the device (Explorer only at this time):


To debug bootloaders with GDB, see Didj JTAG How To.


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.


Didj JTAG How To


Low-cost Bitbang JTAG using the FTDI FT232

To do