On Tue, Oct 15, 2013 at 10:29 AM, Paul Fertser <[email protected]> wrote:
>
>
> 1. http://openocd.zylin.com/1516 without this change it's impossible
> to put MSP430 into JTAG mode, that's needed if you have it in the
> chain with some other supported target. Unfortunately, this is not
> enough as MSP430 needs the magic sequence to be done faster than what
> we can get this way. http://openocd.zylin.com/#/c/1550/ this was
> supposed to solve, and is known to work on real hardware. Andreas,
> what do you propose instead?
>
Well, the obvious solution would be to *not* put non-JTAG devices in the
JTAG chain. If someone is determined to do so anyway, they could use a
suitable instrument such as a waveform generator to toggle the required
pins before connecting the JTAG debug tool. It's kind of out of scope for
OpenOCD.
If someone wants to persuade OpenOCD into generating the necessary
waveforms, and want to make sure it works for all (conforming) adapters, I
suggest to interleave calls to jtag_add_reset(-ish) and jtag_add_delay to
get the right toggle rate. Unfortunately the current jtag_add_reset does
way too much to be usable for that purpose (for one thing, the jtag_add_*
functions are queued so why the heck does it execute the queue??). However,
the JTAG API is not really designed for bitbanging the reset signals so it
would all be rather hackish anyway. Nothing in the API can guarantee you a
*minimum* toggle rate, only a maximum (and only if explicit delays are
added; the adapter_khz setting doesn't necessarily apply to anything other
than scans AFAIK).
The 1550 change does it wrong in at least two ways:
1. It changes the semantics of the jtag_reset command (it skips all the
extra stuff that jtag_add_reset does, wrong as it may be).
2. It gives no guarantee as to what the actual toggle rate will be. The
JTAG API provides no such guarantee so neither can this nor any similar
patch.
/Andreas
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