Hardware documentation mp900c jtag
From JLiMe.com
Contents |
About
In short Jtag is a way to gain complete control over your handheld. It can listen/alter the communication stream between the different parts of the hardware.
Most useful aspects for the mp900c is that you can debug code and reflash without any worry of bricking the device. You can read more about Jtag on wikipedia here
Howto
The goal is to create an adapter that fits into the JTAG connector pictured below.
This connector is a Molex PicoBlade socket. To build a cable that fits this, you can order the Molex connector and contacts from DigiKey:
The connector is NOT a Molex PicoBlade socket. I just received the the connectors from DigiKey and they do not fit:
Since I still can't find a plug to fit the JTAG socket, I decided to look for a good way to make contact with the JTAG contacts in the CF slot without having to solder wires directly to the motherboard. What I discovered was that xD flash cards have the exact same contact width and spacing as the JTAG contacts on the mp900 mobo. So I gutted a multi-cart reader to cut out the xD socket contacts. I then glued them to a CF card in the correct spot and soldered my GoodFET JTAG cable to it:
and a closeup:
I have yet to fully test this, but in theory it works. Getting the contacts glued just right is nearly impossible. I taped the contacts to the mobo it the correct position, then put glue on the back and slid a CF card into the slot so that contacts glued to the CF card. If this isn't reliable enough, I'll just solder directly to the mobo.
GoodFET JTAG
Travis Goodspeed has been quite neighborly with the creation and release of his opensource/openhardware GoodFET line of USB to JTAG adapters. The GoodFET boards use an MSP430 microcontroller and speak a simple protocol to the PC. The PC side libraries are all written in Python and are quite hackable.
I am currently building a couple of GoodFET 21's for hacking my mp900. I will be running the barebones JTAG firmware and will be building the mp900 JTAG commands on top of that (cribbing heavily from the JTAG tools that can already talk to the mp900).
The schematic for the GoodFET 21 looks like:
The cable connecting the GoodFET to the mp900 looks like:
GoodFET mp900 TDO pin 1 ------- TDO pin 7 TDI pin 3 ------- TDI pin 4 TMS pin 5 ------- TMS pin 3 TCK pin 7 ------- TCK pin 1 GND pin 9 ------- GND pin 8
Parallel Port JTAG Cable Schematics
NOTE: Below is a schematic for a JTAG cable for connecting to the JTAG contacts under the CF card socket. The pin numbers on the mp900 side correspond to those contacts and NOT the pins in the other JTAG socket shown above. However this cable could be made to work with the Molex Socket shown above.
