Commit 4e56a230 authored by David Brownell's avatar David Brownell
Browse files

target: groundwork for "reset-assert" event

This defines a "reset-assert" event and a supporting utility
routine, and documents both how targets should implement it
and how config scripts should use it.  Core-specific updates
are needed to make this work.
Signed-off-by: default avatarDavid Brownell <>
parent 4d2750e5
......@@ -1411,6 +1411,20 @@ chip can be tweaked by the board.
Some chips have specific ways the TRST and SRST signals are
managed. In the unusual case that these are @emph{chip specific}
and can never be changed by board wiring, they could go here.
For example, some chips can't support JTAG debugging without
both signals.
Provide a @code{reset-assert} event handler if you can.
Such a handler uses JTAG operations to reset the target,
letting this target config be used in systems which don't
provide the optional SRST signal, or on systems where you
don't want to reset all targets at once.
Such a handler might write to chip registers to force a reset,
use a JRC to do that (preferable -- the target may be wedged!),
or force a watchdog timer to trigger.
(For Cortex-M3 targets, this is not necessary. The target
driver knows how to use trigger an NVIC reset when SRST is
not available.)
Some chips need special attention during reset handling if
they're going to be used with JTAG.
......@@ -1418,6 +1432,8 @@ An example might be needing to send some commands right
after the target's TAP has been reset, providing a
@code{reset-deassert-post} event handler that writes a chip
register to report that JTAG debugging is being done.
Another would be reconfiguring the watchdog so that it stops
counting while the core is halted in the debugger.
JTAG clocking constraints often change during reset, and in
some cases target config files (rather than board config files)
......@@ -2401,6 +2417,12 @@ There are also @emph{event handlers} associated with TAPs or Targets.
Those handlers are Tcl procedures you can provide, which are invoked
at particular points in the reset sequence.
@emph{When SRST is not an option} you must set
up a @code{reset-assert} event handler for your target.
For example, some JTAG adapters don't include the SRST signal;
and some boards have multiple targets, and you won't always
want to reset everything at once.
After configuring those mechanisms, you might still
find your board doesn't start up or reset correctly.
For example, maybe it needs a slightly different sequence
......@@ -3390,9 +3412,14 @@ For example:
@itemize @bullet
@item What should happen when GDB connects? Should your target reset?
@item When GDB tries to flash the target, do you need to enable the flash via a special command?
@item Is using SRST appropriate (and possible) on your system?
Or instead of that, do you need to issue JTAG commands to trigger reset?
SRST usually resets everything on the scan chain, which can be inappropriate.
@item During reset, do you need to write to certain memory locations
to set up system clocks or
to reconfigure the SDRAM?
How about configuring the watchdog timer, or other peripherals,
to stop running while you hold the core stopped for debugging?
@end itemize
All of the above items can be addressed by target event handlers.
......@@ -3457,16 +3484,28 @@ The following target events are defined:
@item @b{reset-assert-pre}
@* Issued as part of @command{reset} processing
after @command{reset_init} was triggered
but before SRST alone is re-asserted on the tap.
but before either SRST alone is re-asserted on the scan chain,
or @code{reset-assert} is triggered.
@item @b{reset-assert}
@* Issued as part of @command{reset} processing
after @command{reset-assert-pre} was triggered.
When such a handler is present, cores which support this event will use
it instead of asserting SRST.
This support is essential for debugging with JTAG interfaces which
don't include an SRST line (JTAG doesn't require SRST), and for
selective reset on scan chains that have multiple targets.
@item @b{reset-assert-post}
@* Issued as part of @command{reset} processing
when SRST is asserted on the tap.
after @code{reset-assert} has been triggered.
or the target asserted SRST on the entire scan chain.
@item @b{reset-deassert-pre}
@* Issued as part of @command{reset} processing
when SRST is about to be released on the tap.
after @code{reset-assert-post} has been triggered.
@item @b{reset-deassert-post}
@* Issued as part of @command{reset} processing
when SRST has been released on the tap.
after @code{reset-deassert-pre} has been triggered
and (if the target is using it) after SRST has been
released on the scan chain.
@item @b{reset-end}
@* Issued as the final step in @command{reset} processing.
......@@ -147,6 +147,7 @@ static const Jim_Nvp nvp_target_event[] = {
{ .value = TARGET_EVENT_RESET_START, .name = "reset-start" },
{ .value = TARGET_EVENT_RESET_ASSERT_PRE, .name = "reset-assert-pre" },
{ .value = TARGET_EVENT_RESET_ASSERT, .name = "reset-assert" },
{ .value = TARGET_EVENT_RESET_ASSERT_POST, .name = "reset-assert-post" },
{ .value = TARGET_EVENT_RESET_DEASSERT_PRE, .name = "reset-deassert-pre" },
{ .value = TARGET_EVENT_RESET_DEASSERT_POST, .name = "reset-deassert-post" },
......@@ -154,8 +155,8 @@ static const Jim_Nvp nvp_target_event[] = {
{ .value = TARGET_EVENT_RESET_HALT_POST, .name = "reset-halt-post" },
{ .value = TARGET_EVENT_RESET_WAIT_PRE, .name = "reset-wait-pre" },
{ .value = TARGET_EVENT_RESET_WAIT_POST, .name = "reset-wait-post" },
{ .value = TARGET_EVENT_RESET_INIT , .name = "reset-init" },
{ .value = TARGET_EVENT_RESET_END, .name = "reset-end" },
{ .value = TARGET_EVENT_RESET_INIT, .name = "reset-init" },
{ .value = TARGET_EVENT_RESET_END, .name = "reset-end" },
{ .value = TARGET_EVENT_EXAMINE_START, .name = "examine-start" },
{ .value = TARGET_EVENT_EXAMINE_END, .name = "examine-end" },
......@@ -3523,6 +3524,20 @@ void target_handle_event(struct target *target, enum target_event e)
* Returns true only if the target has a handler for the specified event.
bool target_has_event_action(struct target *target, enum target_event event)
struct target_event_action *teap;
for (teap = target->event_action; teap != NULL; teap = teap->next) {
if (teap->event == event)
return true;
return false;
enum target_cfg_param {
......@@ -196,6 +196,7 @@ enum target_event
TARGET_EVENT_RESET_ASSERT, /* C code uses this instead of SRST */
......@@ -226,7 +227,9 @@ struct target_event_action {
struct Jim_Obj *body;
int has_percent;
struct target_event_action *next;
bool target_has_event_action(struct target *target, enum target_event event);
struct target_event_callback
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