From my experiments, it appears to be don't-care for TMS. They just need 100 TCK pulses to flip the bit to enable the JTAG power domain.
--
Rick Altherr
[email protected]

"He said he hadn't had a byte in three days. I had a short, so I split it with him."
 -- Unsigned



On Jun 10, 2009, at 1:28 PM, David Brownell wrote:

On Wednesday 10 June 2009, David Brownell wrote:
  http://tiexpressdsp.com/index.php/ICEPICK

The "how to add devices to an ICEpick-C scan chain" highlights
one point:  the JRC commands to add the ARM (and, for DaVinci,
the ETB) to the scan chain must be done each time the TAPs go
to the RESET state (via TMS or nTRST).

Hmm, and also:

        Before starting the debugger, the debug power domain must
        be activated by applying a minimum of 100 (free running)
        TCK pulses to the device after nTRST is pulled high.

It's not clear whether that means TMS high, low, or don't-care.
Does anyone know?

If it's not "TMS low" then I wonder if it's practical to make normal
startup processing -- or entry to JTAG's RESET state -- always do
that.  Could it hurt anything?

If "TMS low" works then it's a bit sad that JRCs aren't targets.
Else the reset-deassert-post handler could just "runtest 100";
those handlers don't kick in for TAPs, just targets.  (Which
seems like a non-useful restriction, FWIW.)

- Dave

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