LeapFrog Pollux Platform: FTDI JTAG How To

Didj FTDI2232 JTAG setup

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

Didj JTAG pads

Didj nSRST pad on opposite side of mainboard from JTAG pads

Leapster Explorer JTAG pads

LeapPad 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, LX and the eGo. 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	LPX Test Pad label	eGo photo label
TRST	17	TP9	RST	RST	nTRST
TDI	16	TP10	TDI	TDI	TDI
TMS	5	TP11	TMS	TMS	TMS
TCK	18	TP12	TCK	TCK	TCK
TDO	2	TP13	TDO	TDO	TDO
(S)RST	13	TP103 [1]	nRST	nRST	nPORST
GND	Either 1 or 10	TP14	GND	GND	use any 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.

[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:

#
# 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] } {
  set  _CHIPNAME $CHIPNAME
} else {
  set  _CHIPNAME pollux
}
if { [info exists ENDIAN] } {
  set  _ENDIAN $ENDIAN
} else {
  set  _ENDIAN little
}
if { [info exists CPUTAPID ] } {
  set _CPUTAPID $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
set _TARGETNAME $_CHIPNAME.cpu
target create $_TARGETNAME arm926ejs -endian $_ENDIAN -chain-position $_TARGETNAME -variant arm926ejs 

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

>halt
>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:

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

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.

References

Didj JTAG How To

DLP-USB1232H_and_OpenOCD_based_JTAG_adapter

Low-cost Bitbang JTAG using the FTDI FT232