1MHz is just as bad as as default as 30MHz. It may work in more cases,
but it is still broken in some.
As I said before the 1Mhz startup frequency could be 10kHz. The
important is not the value of the startup frequency, the important is to
know we have a startup frequency !!!
IMHO, there are two possibilities:
- we find a method to auto-configure a default that works in *every* case
That's the best to do at the end.
- or we require a configuration value that works (that may be chip- or
board-specific).
Will be never good. A JTAG frequency is not only board specific, but
wire (cable length) dependent, buffer dependend, dongle dependent ....
Too many parameters !!!
Having a default that works most of the time, but causes strange effects
in some cases, is really bad useability.
The question is what is 'most of time' 80% 90% 99%
Fixing at a default 10KHz frequency will help user to auto-detect their
JTAG chain ... and this is REALLY ever a GOOD thing to know the JTAG
chain is auto-detected -> my JTAG Chain is working, the JTAG transport
layer is working, user are already happy ;-)
Next, is to find the max. safe frequency :-)
>/ THE SAFE CORRECT ROBUST frequency can never be known as static ! A
/>/ good JTAG software has to find this frequency by itself
/>/ (auto-detecting the max safe JTAG frequency );-)
/Then how do you propose to implement such an auto-detection?
Work on 10KHz startup frequency.
READ the TAPID_old (the first TAP ID is enough)
READ the TAPID_new (the first TAP ID is enough)
WHILE TAPID_old = TAPID_new old
up/scale the frequency
TAPID_old <= TAPID_new;
READ the TAPID_new (the first TAP ID is enough)
DO
max safe frequency is TAPID_old
>/ The default frequency could be 10KHz instead 1MHZ ...
/Until some new really-low-power chip comes along that starts at an even
lower internal clock - this does not sound robust.
I am almost sure at 10KHz it will be 99% robust -> not enough !
Laurent
Amontec JTAGkey-2 Hi-SPEED USB JTAG CABLE
http://www.amontec.com
_______________________________________________
Openocd-development mailing list
Openocd-development@lists.berlios.de
https://lists.berlios.de/mailman/listinfo/openocd-development
