Re: [f-cpu] today's idea : JTAG console !

[Graham Seaman <graham@seul.org>]

On Wed, 9 Oct 2002 whygee@club-internet.fr wrote:

> hi !
> 
> are there some IC test specialists in this list ?
> how many people have used and programmed tools
> for the JTAG interface ?

There's a discussion on jtag software/hardware  (ie driver
hardware, not the internal implementation) going on the
the geda-dev mailing list archived at geda.seul.org at the moment
 - see the 'gtag' thread. You may find a link to relevant software
there.

Graham


> 
> This synchronous interface uses a few wires and
> it's a wide-spread IEEE standard that is used to
> test PCB traces, IC internal units, program and check
> FPGAs, configure systems... There is a relatively good
> article about this in Elektor (available now in France)
> and there are many resources about this on the Net.
> 
> Today's idea is to add an architecture-specific
> (shift) register that can be used to communicate
> with the core itself, without any need for serial
> RS232 ports etc. This JTAG register is split in
> 2 parts, one for writing and another for reading,
> so the host (whatever type) can send bytes to the
> CPU and the CPU can answer. Some kind of protocol
> must be defined (a flag must be used to specify
> if the last byte has been "consumed" or "read" by
> the target) but it will remain very simple.
> 
> A more sophisticated SW layer can be made on this,
> allowing very simple debugging and development,
> either emulated, simulated or in HW, with very few
> efforts. Because it only needs 2 SRs and a few wires
> that are used for testing only, it requires very few HW
> resources and it is compatible with most existing test
> devices.
> 
> I have already used (a bit) JTAG at the university
> but i don't trust their programs (which i believe
> to break most standards and good taste). So i would like
> to ask the listees whether they have used or programmed
> GPL'd code for JTAG ?
> 
> Is somebody wanting to be responsible for the design of
> this unit and of the JTAG interface ?
> 
> YG
> (sorry if this post is a bit messy)
> 
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