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add documentation about reset customization

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We added two overridable procedures; document them, and the
two jtag arp_* operations they necessarily expose.

Update the comment about the jtag_init_reset() routine; it's
been obsolete for as long as it's had SRST support.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
This commit is contained in:
David Brownell
2009-10-09 12:52:42 -07:00
parent c3428f5b7a
commit bc13c12be9
2 changed files with 127 additions and 22 deletions
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29
src/jtag/core.c
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@@ -1360,22 +1360,31 @@ int jtag_init_reset(struct command_context_s *cmd_ctx)
if ((retval = jtag_interface_init(cmd_ctx)) != ERROR_OK)
return retval;
LOG_DEBUG("Trying to bring the JTAG controller to life by asserting TRST / TLR");
LOG_DEBUG("Initializing with hard TRST+SRST reset");
/* Reset can happen after a power cycle.
/*
* This procedure is used by default when OpenOCD triggers a reset.
* It's now done through an overridable Tcl "init_reset" wrapper.
*
* Ideally we would only assert TRST or run TLR before the target reset.
* This started out as a more powerful "get JTAG working" reset than
* jtag_init_inner(), applying TRST because some chips won't activate
* JTAG without a TRST cycle (presumed to be async, though some of
* those chips synchronize JTAG activation using TCK).
*
* However w/srst_pulls_trst, trst is asserted together with the target
* reset whether we want it or not.
* But some chips only activate JTAG as part of an SRST cycle; SRST
* got mixed in. So it became a hard reset routine, which got used
* in more places, and which coped with JTAG reset being forced as
* part of SRST (srst_pulls_trst).
*
* NB! Some targets have JTAG circuitry disabled until a
* trst & srst has been asserted.
* And even more corner cases started to surface: TRST and/or SRST
* assertion timings matter; some chips need other JTAG operations;
* TRST/SRST sequences can need to be different from these, etc.
*
* NB! here we assume nsrst/ntrst delay are sufficient!
*
* NB! order matters!!!! srst *can* disconnect JTAG circuitry
* Systems should override that wrapper to support system-specific
* requirements that this not-fully-generic code doesn't handle.
*
* REVISIT once Tcl code can read the reset_config modes, this won't
* need to be a C routine at all...
*/
jtag_add_reset(1, 0); /* TAP_RESET, using TMS+TCK or TRST */
if (jtag_reset_config & RESET_HAS_SRST)