how to jtag your 900/900c
if your 900 or 900c suddenly stops powering up, maybe after a system
crash or just on its own after a reboot,
then it probably has a corrupt bootloader image, but otherwise
perfectly working hardware.
or if you flashed the device in the wrong way (oops) that resulted in
well, here's the ultimate last chance solution.
what you need:
- PC with windows (98 or later), or linux works too, but this
description applies to windows
- if you are on windows, then also cygwin from http://cygwin.com
- parallel port on PC
- jtag cable, schematics for a working example (very simple!!) here: http://hpcmonex.net/nec900/files/jtag/900c_jtag.jpg
note, this emulates a wiggler cable... you can also order some more
serious type of wiggler but that costs more.
- soldering iron and the right screwdriver to disassemble the 900c
- bootloader file
- jtag tools 0.5.1, here's a version compiled for cygwin: http://hpcmonex.net/nec900/files/jtag/jtag900cfinal.zip
1. after you got all the above, disassemble the 900c, hpcnec has
a disassembly guide here: http://hpcnec.com/cgi-bin/hpcnec.cgi?fid=15&topic_id=1204570453
2. solder the jtag cable to the jtag pins on the 900c like
this: in this
picture and sort out the LPT end on the PC too.
NOTE: an alternative jtag header and pinout exists on the motherboard, for more information refer to the hpcfactor thread linked at the bottom of this page.
3. now to make the software work... assuming you are on windows,
download and install cygwin from http://cygwin.com. when
it gets to ask you about which packages to download,
leave all that on default except for an extra package you need, it's
ioperm under Devel packages.
4. using cmd.exe, cmd into cygwin\bin and run this command: ioperm
5. after that, here is the already compiled jtag tools for
cygwin in windows: jtag900cfinal.zip.
download and unzip that to cygwin\home\yourusername\jtag.
then copy the jtag folder within usr\local\share from
jtag900cfinal.zip into cygwin\usr\local\share\jtag
now it's all
to start jtag tools, run cygwin from the cygwin icon on desktop or
start menu, and from the cmd it opens, issue this command: cd jtag,
then issue this command: cd src, finally issue this: ./jtag
6. connect the 900c if you haven't already, and power it up by
simply inserting the battery and putting it on AC power as well! type
this command: cable parallel 0x378 WIGGLER
(check if your parallel port is indeed on 0x378, in device manager, lpt
port, resources) it should say Initializing ...
of course, if you have a non wiggler cable that is supported by jtag
tools then use the name of that instead.
7. then type this command: detect
this should tell you your CPU is a PXA255A0.
if it doesn't return
anything, make sure the device is on AC properly / battery is fully
charged. the point is that the board must be powered on for detect to work.
8. next command is: detectflash
that should return lots of info on the flash
9. now try reading your current bootloader image: readmem
0x0 0x80000 filename
you can check its contents or compare it to saboot.nb0 bootloader image
to see if it is the same... if not then it's probably corrupt and you
have a good chance to revive the device.
10. now flash the file you extracted from the bootloader download:
flashmem msbin saboot.xip
if verification is ok, then you are almost finished now.
11. disconnect from the PC, remove power from 900c, and try
reinserting battery and powering up. it should boot up now! if not then
maybe something went wrong, try jtag again. note, it's fine if it
doesn't boot to OS, just bootloader. you jtagged bootloader 4.10 in, so feel free to just reflash an OS!
1. if you had a 900 running hpc2000 OS then the above posted bootloader
will not boot the OS. but the solution is simple: you can choose to
keep hpc2000 or upgrade to cenet.
if you want hpc2000, then just download and flash this
hpc2000 image compatible with cenet bootloader. if you want ce.net
then download stock cenet rom from my download page
(select any of the options except "Not listed").
then, flash the image from CF card using C+F method (how to described at this link).
2. if cygwin won't run jtag tools then read more for a solution: 1)
somewhere else on your PC outside cygwin folder. 2) take the cygwindlls
folder from the extracted jtag900cfinal.zip and copy the dlls from it into
\src folder. 3) then copy the jtag folder within usr\local\share from
jtag900cfinal.zip into cygwin\usr\local\share\jtag. 4) then, simply
(using windows cmd.exe) cmd into the \src folder where you copied the
cygwindlls folder contents too and type the command jtag to run jtag tools. hopefully
3. for more information, you can read the original 900c jtag thread at:
this also describes an alternative pinout for jtag, but as a sumup it is:
on the white JTAG connector under the modem: test - 8, nTRST 9, TCK 1, TMS 3, TDI 5, TDO 10, A1-DC3,3V