+@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{Watchdog Timers}...
+Watchog timers are typically used to automatically reset systems if
+some application task doesn't periodically reset the timer. (The
+assumption is that the system has locked up if the task can't run.)
+When a JTAG debugger halts the system, that task won't be able to run
+and reset the timer ... potentially causing resets in the middle of
+your debug sessions.
+
+It's rarely a good idea to disable such watchdogs, since their usage
+needs to be debugged just like all other parts of your firmware.
+That might however be your only option.
+
+Look instead for chip-specific ways to stop the watchdog from counting
+while the system is in a debug halt state. It may be simplest to set
+that non-counting mode in your debugger startup scripts. You may however
+need a different approach when, for example, a motor could be physically
+damaged by firmware remaining inactive in a debug halt state. That might
+involve a type of firmware mode where that "non-counting" mode is disabled
+at the beginning then re-enabled at the end; a watchdog reset might fire
+and complicate the debug session, but hardware (or people) would be
+protected.@footnote{Note that many systems support a "monitor mode" debug
+that is a somewhat cleaner way to address such issues. You can think of
+it as only halting part of the system, maybe just one task,
+instead of the whole thing.
+At this writing, January 2010, OpenOCD based debugging does not support
+monitor mode debug, only "halt mode" debug.}
+
+@item @b{ARM Semihosting}...
+@cindex ARM semihosting
+When linked with a special runtime library provided with many
+toolchains@footnote{See chapter 8 "Semihosting" in
+@uref{http://infocenter.arm.com/help/topic/com.arm.doc.dui0203i/DUI0203I_rvct_developer_guide.pdf,
+ARM DUI 0203I}, the "RealView Compilation Tools Developer Guide".
+The CodeSourcery EABI toolchain also includes a semihosting library.},
+your target code can use I/O facilities on the debug host. That library
+provides a small set of system calls which are handled by OpenOCD.
+It can let the debugger provide your system console and a file system,
+helping with early debugging or providing a more capable environment
+for sometimes-complex tasks like installing system firmware onto
+NAND or SPI flash.
+
+@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.@footnote{As a more
+polite alternative, some processors have special debug-oriented
+registers which can be used to change various features including
+how the low power states are clocked while debugging.
+The STM32 DBGMCU_CR register is an example; at the cost of extra
+power consumption, JTAG can be used during low power states.}
+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
+
+@section Target Hardware Setup
+
+Chip vendors often provide software development boards which
+are highly configurable, so that they can support all options
+that product boards may require. @emph{Make sure that any
+jumpers or switches match the system configuration you are
+working with.}
+
+Common issues include:
+
+@itemize @bullet
+
+@item @b{JTAG setup} ...
+Boards may support more than one JTAG configuration.
+Examples include jumpers controlling pullups versus pulldowns
+on the nTRST and/or nSRST signals, and choice of connectors
+(e.g. which of two headers on the base board,
+or one from a daughtercard).
+For some Texas Instruments boards, you may need to jumper the
+EMU0 and EMU1 signals (which OpenOCD won't currently control).
+
+@item @b{Boot Modes} ...
+Complex chips often support multiple boot modes, controlled
+by external jumpers. Make sure this is set up correctly.
+For example many i.MX boards from NXP need to be jumpered
+to "ATX mode" to start booting using the on-chip ROM, when
+using second stage bootloader code stored in a NAND flash chip.
+
+Such explicit configuration is common, and not limited to
+booting from NAND. You might also need to set jumpers to
+start booting using code loaded from an MMC/SD card; external
+SPI flash; Ethernet, UART, or USB links; NOR flash; OneNAND
+flash; some external host; or various other sources.
+
+
+@item @b{Memory Addressing} ...
+Boards which support multiple boot modes may also have jumpers
+to configure memory addressing. One board, for example, jumpers
+external chipselect 0 (used for booting) to address either
+a large SRAM (which must be pre-loaded via JTAG), NOR flash,
+or NAND flash. When it's jumpered to address NAND flash, that
+board must also be told to start booting from on-chip ROM.
+
+Your @file{board.cfg} file may also need to be told this jumper
+configuration, so that it can know whether to declare NOR flash
+using @command{flash bank} or instead declare NAND flash with
+@command{nand device}; and likewise which probe to perform in
+its @code{reset-init} handler.
+
+A closely related issue is bus width. Jumpers might need to
+distinguish between 8 bit or 16 bit bus access for the flash
+used to start booting.
+
+@item @b{Peripheral Access} ...
+Development boards generally provide access to every peripheral
+on the chip, sometimes in multiple modes (such as by providing
+multiple audio codec chips).
+This interacts with software
+configuration of pin multiplexing, where for example a
+given pin may be routed either to the MMC/SD controller
+or the GPIO controller. It also often interacts with
+configuration jumpers. One jumper may be used to route
+signals to an MMC/SD card slot or an expansion bus (which
+might in turn affect booting); others might control which
+audio or video codecs are used.
+
+@end itemize
+
+Plus you should of course have @code{reset-init} event handlers
+which set up the hardware to match that jumper configuration.
+That includes in particular any oscillator or PLL used to clock
+the CPU, and any memory controllers needed to access external
+memory and peripherals. Without such handlers, you won't be
+able to access those resources without working target firmware
+which can do that setup ... this can be awkward when you're
+trying to debug that target firmware. Even if there's a ROM
+bootloader which handles a few issues, it rarely provides full
+access to all board-specific capabilities.
+