Commit bde4a404 authored by dbrownell's avatar dbrownell
Browse files

Doc updates: add section on target software changes, minor fixes


git-svn-id: svn://svn.berlios.de/openocd/trunk@2774 b42882b7-edfa-0310-969c-e2dbd0fdcd60
parent d96e3eae
......@@ -845,6 +845,54 @@ the main bootloader code (which won't fit into that SRAM).
Other helper scripts might be used to write production system images,
involving considerably more than just a three stage bootloader.
@section Target Software Changes
Sometimes you may want to make some small changes to the software
you're developing, to help make JTAG debugging work better.
For example, in C or assembly language code you might
use @code{#ifdef JTAG_DEBUG} (or its converse) around code
handling issues like:
@itemize @bullet
@item @b{ARM Wait-For-Interrupt}...
Many ARM chips synchronize the JTAG clock using the core clock.
Low power states which stop that core clock thus prevent JTAG access.
Idle loops in tasking environments often enter those low power states
via the @code{WFI} instruction (or its coprocessor equivalent, before ARMv7).
You may want to @emph{disable that instruction} in source code,
or otherwise prevent using that state,
to ensure you can get JTAG access at any time.
For example, the OpenOCD @command{halt} command may not
work for an idle processor otherwise.
@item @b{Delay after reset}...
Not all chips have good support for debugger access
right after reset; many LPC2xxx chips have issues here.
Similarly, applications that reconfigure pins used for
JTAG access as they start will also block debugger access.
To work with boards like this, @emph{enable a short delay loop}
the first thing after reset, before "real" startup activities.
For example, one second's delay is usually more than enough
time for a JTAG debugger to attach, so that
early code execution can be debugged
or firmware can be replaced.
@item @b{Debug Communications Channel (DCC)}...
Some processors include mechanisms to send messages over JTAG.
Many ARM cores support these, as do some cores from other vendors.
(OpenOCD may be able to use this DCC internally, speeding up some
operations like writing to memory.)
Your application may want to deliver various debugging messages
over JTAG, by @emph{linking with a small library of code}
provided with OpenOCD and using the utilities there to send
various kinds of message.
@xref{Software Debug Messages and Tracing}.
@end itemize
@node Config File Guidelines
@chapter Config File Guidelines
......@@ -2462,7 +2510,7 @@ If necessary, disables the tap
by sending it a @option{tap-disable} event.
Returns the string "1" if the tap
specified by @var{dotted.name} is enabled,
and "0" if it is disbabled.
and "0" if it is disabled.
@end deffn
@deffn Command {jtag tapenable} dotted.name
......@@ -2470,13 +2518,13 @@ If necessary, enables the tap
by sending it a @option{tap-enable} event.
Returns the string "1" if the tap
specified by @var{dotted.name} is enabled,
and "0" if it is disbabled.
and "0" if it is disabled.
@end deffn
@deffn Command {jtag tapisenabled} dotted.name
Returns the string "1" if the tap
specified by @var{dotted.name} is enabled,
and "0" if it is disbabled.
and "0" if it is disabled.
@quotation Note
Humans will find the @command{scan_chain} command more helpful
......@@ -5600,7 +5648,7 @@ as used by Linux with CONFIG_DEBUG_ICEDCC;
otherwise the libdcc format is used.
@end deffn
@deffn Command {trace history} (@option{clear}|count)
@deffn Command {trace history} [@option{clear}|count]
With no parameter, displays all the trace points that have triggered
in the order they triggered.
With the parameter @option{clear}, erases all current trace history records.
......@@ -5608,7 +5656,7 @@ With a @var{count} parameter, allocates space for that many
history records.
@end deffn
@deffn Command {trace point} (@option{clear}|identifier)
@deffn Command {trace point} [@option{clear}|identifier]
With no parameter, displays all trace point identifiers and how many times
they have been triggered.
With the parameter @option{clear}, erases all current trace point counters.
......
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