Hi all,
One problem occurs regarding the JTAG frequency, the JTAG Dongle and the
script compatibility :
The Amontec JTAGkey first generation (JTAGkey and JTAGkey Tiny) are
running at a maximum 6MHz .
The Amontec JTAGkey second generation (JTAGkey-2 JTAGkey-2P soon
JTAGkey-2 Tiny) are running at a maximum JTAG Frequency 30MHz
The Amontec JTAGkey third generation (JTAGkey-3) will run at a maximum
of 60Mhz JTAG Frequency.
The problem:
A lot of customers using both Amontec JTAGkey and Amontec JTAGkey-2 come
with the comment : "the JTAGkey-2 is not working with OpenOCD, but the
JTAGkey works ".
The problem is just coming from a too high JTAG Frequency when using
Amontec JTAGkey-2.
In fact, at the startup of OpenOCD, the JTAG frequency is set by default
to the maximum JTAG Frequency of the Dongle (for Amonte JTAGkey-2 30Mhz)
But a 30MHz JTAG Frequency is too high for a lot of system .
The workaround:
The workaround for the end-user is to customize their script with adding
the command 'adapter_khz' to reduce the JTAG frequency when using a
JTAGkey-2 second generation, as
adapter_khz 6000
or higher by doing some tests and by searching the maximum JTAG
freqeuncy of their system;-) ...
But this will be customization depending on both the Dongle capability
and the JTAG chain itself, see NOTE 2.
The solutions :
1. the solution will be to implement in openocd a function for
auto-detecting the maximum JTAG frequency capability of the system.
IMPORTANT NOTES :
1.
Here the big advantage of RTCK signal support from Amontec JTAGkey-2
If your processor has the RTCK signal, you do not need to do this
exercise of detecting the maximum frequency of the JTAG chain.
Just enable the RTCK to the Amontec JTAGkey-2, and the dongle will adapt
the JTAG frequency using RTCK ;-)
2.
The frequency of the JTAG chain depends on many factors :
- The target processor, only new devices accept TCK JTAG frequency up to
30MHz and/or more
- The number of target in the chain (capacity of the JTAG signals)
- The integrity (termination) of the JTAG signals on the target board
- The length of the JTAG Cable (inductance on the JTAG signals)
- The JTAG Dongle itself (how good are the buffer and the terminations
(resistor, capacity ...)
But for the end-user this factor are even unknown !
Regards,
Laurent Gauch
http://www.amontec.com/
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