From bc13c12be96fab35cb2f25df4f37c283cca70b98 Mon Sep 17 00:00:00 2001 From: David Brownell Date: Fri, 9 Oct 2009 12:52:42 -0700 Subject: [PATCH] add documentation about reset customization 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 --- doc/openocd.texi | 120 ++++++++++++++++++++++++++++++++++++++++++----- src/jtag/core.c | 29 ++++++++---- 2 files changed, 127 insertions(+), 22 deletions(-) diff --git a/doc/openocd.texi b/doc/openocd.texi index daa94609..bf80e123 100644 --- a/doc/openocd.texi +++ b/doc/openocd.texi @@ -1563,6 +1563,17 @@ read/write memory on your target, @command{init} must occur before the memory read/write commands. This includes @command{nand probe}. @end deffn +@deffn {Overridable Procedure} jtag_init +This is invoked at server startup to verify that it can talk +to the scan chain (list of TAPs) which has been configured. + +The default implementation first tries @command{jtag arp_init}, +which uses only a lightweight JTAG reset before examining the +scan chain. +If that fails, it tries again, using a harder reset +from the overridable procedure @command{init_reset}. +@end deffn + @anchor{TCP/IP Ports} @section TCP/IP Ports @cindex TCP port @@ -2192,8 +2203,9 @@ issues (not limited to errata). For example, certain JTAG commands might need to be issued while the system as a whole is in a reset state (SRST active) but the JTAG scan chain is usable (TRST inactive). -(@xref{JTAG Commands}, where the @command{jtag_reset} -command is presented.) +Many systems treat combined assertion of SRST and TRST as a +trigger for a harder reset than SRST alone. +Such custom reset handling is discussed later in this chapter. @end itemize There can also be other issues. @@ -2260,7 +2272,7 @@ Possible values are @option{none} (the default), @option{trst_only}, @quotation Tip If your board provides SRST and/or TRST through the JTAG connector, -you must declare that or else those signals will not be used. +you must declare that so those signals can be used. @end quotation @item @@ -2309,6 +2321,81 @@ powerup and pressing a reset button. @end itemize @end deffn +@section Custom Reset Handling + +OpenOCD has several ways to help support the various reset +mechanisms provided by chip and board vendors. +The commands shown in the previous section give standard parameters. +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. + +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 +of SRST and/or TRST manipulations, because of quirks that +the @command{reset_config} mechanism doesn't address; +or asserting both might trigger a stronger reset, which +needs special attention. + +Experiment with lower level operations, such as @command{jtag_reset} +and the @command{jtag arp_*} operations shown here, +to find a sequence of operations that works. +@xref{JTAG Commands}. +When you find a working sequence, it can be used to override +@command{jtag_init}, which fires during OpenOCD startup +(@pxref{Configuration Stage}); +or @command{init_reset}, which fires during reset processing. + +You might also want to provide some project-specific reset +schemes. For example, on a multi-target board the standard +@command{reset} command would reset all targets, but you +may need the ability to reset only one target at time and +thus want to avoid using the board-wide SRST signal. + +@deffn {Overridable Procedure} init_reset mode +This is invoked near the beginning of the @command{reset} command, +usually to provide as much of a cold (power-up) reset as practical. +By default it is also invoked from @command{jtag_init} if +the scan chain does not respond to pure JTAG operations. +The @var{mode} parameter is the parameter given to the +low level reset command (@option{halt}, +@option{init}, or @option{run}), @option{setup}, +or potentially some other value. + +The default implementation just invokes @command{jtag arp_init-reset}. +Replacements will normally build on low level JTAG +operations such as @command{jtag_reset}. +Operations here must not address individual TAPs +(or their associated targets) +until the JTAG scan chain has first been verified to work. + +Implementations must have verified the JTAG scan chain before +they return. +This is done by calling @command{jtag arp_init} +(or @command{jtag arp_init-reset}). +@end deffn + +@deffn Command {jtag arp_init} +This validates the scan chain using just the four +standard JTAG signals (TMS, TCK, TDI, TDO). +It starts by issuing a JTAG-only reset. +Then it performs checks to verify that the scan chain configuration +matches the TAPs it can observe. +Those checks include checking IDCODE values for each active TAP, +and verifying the length of their instruction registers using +TAP @code{-ircapture} and @code{-irmask} values. +If these tests all pass, TAP @code{setup} events are +issued to all TAPs with handlers for that event. +@end deffn + +@deffn Command {jtag arp_init-reset} +This uses TRST and SRST to try resetting +everything on the JTAG scan chain +(and anything else connected to SRST). +It then invokes the logic of @command{jtag arp_init}. +@end deffn + @node TAP Declaration @chapter TAP Declaration @@ -2540,9 +2627,6 @@ there seems to be no problems with JTAG scan chain operations. @section Other TAP commands -@c @deffn Command {jtag arp_init-reset} -@c ... more or less "toggle TRST ... and SRST too, what the heck" - @deffn Command {jtag cget} dotted.name @option{-event} name @deffnx Command {jtag configure} dotted.name @option{-event} name string At this writing this TAP attribute @@ -3218,7 +3302,7 @@ The following target events are defined: @end ignore @item @b{reset-assert-pre} @* Issued as part of @command{reset} processing -after SRST and/or TRST were activated and deactivated, +after @command{reset_init} was triggered but before SRST alone is re-asserted on the tap. @item @b{reset-assert-post} @* Issued as part of @command{reset} processing @@ -3248,10 +3332,11 @@ multiplexing, and so on. the target clocks are fully set up.) @item @b{reset-start} @* Issued as part of @command{reset} processing -before either SRST or TRST are activated. +before @command{reset_init} is called. -This is the most robust place to switch to a low JTAG clock rate, if -SRST disables PLLs needed to use a fast clock. +This is the most robust place to use @command{jtag_rclk} +or @command{jtag_khz} to switch to a low JTAG clock rate, +when reset disables PLLs needed to use a fast clock. @ignore @item @b{reset-wait-pos} @* Currently not used @@ -5983,6 +6068,17 @@ The @command{reset_config} command should already have been used to configure how the board and JTAG adapter treat these two signals, and to say if either signal is even present. @xref{Reset Configuration}. + +Note that TRST is specially handled. +It actually signifies JTAG's @sc{reset} state. +So if the board doesn't support the optional TRST signal, +or it doesn't support it along with the specified SRST value, +JTAG reset is triggered with TMS and TCK signals +instead of the TRST signal. +And no matter how that JTAG reset is triggered, once +the scan chain enters @sc{reset} with TRST inactive, +TAP @code{post-reset} events are delivered to all TAPs +with handlers for that event. @end deffn @deffn Command {runtest} @var{num_cycles} @@ -6015,7 +6111,7 @@ The @var{tap_state} names used by OpenOCD in the @command{drscan}, and @command{irscan} commands are: @itemize @bullet -@item @b{RESET} ... should act as if TRST were active +@item @b{RESET} ... acts as if TRST were pulsed @item @b{RUN/IDLE} ... don't assume this always means IDLE @item @b{DRSELECT} @item @b{DRCAPTURE} @@ -6046,7 +6142,7 @@ may not be as expected. @item @sc{run/idle}, @sc{drpause}, and @sc{irpause} are reasonable choices after @command{drscan} or @command{irscan} commands, since they are free of JTAG side effects. -However, @sc{run/idle} may have side effects that appear at other +@item @sc{run/idle} may have side effects that appear at non-JTAG levels, such as advancing the ARM9E-S instruction pipeline. Consult the documentation for the TAP(s) you are working with. @end itemize diff --git a/src/jtag/core.c b/src/jtag/core.c index 1c9d13c9..14c28fb7 100644 --- a/src/jtag/core.c +++ b/src/jtag/core.c @@ -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. - * - * Ideally we would only assert TRST or run TLR before the target reset. + /* + * This procedure is used by default when OpenOCD triggers a reset. + * It's now done through an overridable Tcl "init_reset" wrapper. * - * However w/srst_pulls_trst, trst is asserted together with the target - * reset whether we want it or not. + * 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). * - * NB! Some targets have JTAG circuitry disabled until a - * trst & srst has been asserted. + * 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! here we assume nsrst/ntrst delay are sufficient! + * 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! 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) -- 2.39.5