Lpc2000

On Sunday 18 December 2005 14:00, Tom Walsh wrote:
> There seems to be a lot of interest on this list at developing an open
> source wiggler gdb tcp server.  Something to replace the OCDaemon.
> While I find that an intriguing idea with a lot of merit, the weakest
> point is still the wiggler electronics and that of the parallel port
> electronics.  The parallel port of a computer is a relatively low-speed
> device, it is not required of it to run megabits of data down to a
> printer.  Therefore, IMO, the chipsets used for a parallel port are
> garbage-variety electronics.

My project has been designed from ground up to be able to support different 
JTAG interfaces. Currently, it supports Wigglers, the FTDI FT2232C and a new 
configuration for the Amontec Chameleon Dongle (not yet released, but works 
really fine - ARM7TDMI RAM download at 60-70kByte/s). I've never used a real 
wiggler or a homemade one, so I don't know about the problems with these, but 
the Amontec Chameleon works just fine. It has a true IEEE1284 transceiver on 
the PC side (guess that guarantees good signal integrity over a long cable 
length) and a Xilinx CoolRunner CPLD (3.3/5V tolerant IO), and I've never had 
any problems with signal integrity at up to 16 MHz JTAG clock (that's for the 
new config, Wiggler wont go beyond 500kHz).

The parallelport is just not designed to do bitbanging - you can transfer 
500-1000 kByte/s using EPP accesses, at a latency of 1-2us.

> What I do think that could be done is an open-source JTAG pod.  Start
> out with something like a Revely RMS101
> (http://www.revely.com/RMS101/AboutRMS101.htm) board, or other low cost
> ARM board which has an ethernet.  Develop the electronics necessary to
> provide good signal conditioning to the Device Under Test's JTAG port.
> Then using that board, build up an open-source jtag solution.  While
> this would cost more than $10 for the electronics, I feel that it would
> be far superior to a wiggler, but still at a fraction of the cost of a
> commercial JTAG unit?  Software of this caliber would then not be
> limited to just one board electronics, others may decide (maybe
> SparkFun?) to further streamline the electronics and offer it at an even
> lower cost?

The software part is mostly independent from the underlying JTAG interface - 
all the tricky logic can be implemented equally well for a wiggler and a much 
smarter (and more expensive) device. This would give users the freedom to 
choose between hobbyist quality at a few $, or some more money for a 
thoroughly designed interface offering high TCK and a failure-proof 
electrical interface - both offering the same functionality.

Personally, I'd favor a FPGA based solution, using USB 2.0. Such a setup would 
allow very high speed at low cost while still offering more flexibility than 
a uC based solution with an Ethernet interface.

Regards,

Dominic Rath