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## 6 Config File Guidelines

This chapter is aimed at any user who needs to write a config file, including developers and integrators of OpenOCD and any user who needs to get a new board working smoothly. It provides guidelines for creating those files.

You should find the following directories under `$(INSTALLDIR)/scripts`, with files including the ones listed here. Use them as-is where you can; or as models for new files.

- `interface` ... These are for debug adapters. Files that configure JTAG adapters go here.

                $ ls interface
                arm-jtag-ew.cfg          hitex_str9-comstick.cfg  oocdlink.cfg
                arm-usb-ocd.cfg          icebear.cfg              openocd-usb.cfg
                at91rm9200.cfg           jlink.cfg                parport.cfg
                axm0432.cfg              jtagkey2.cfg             parport_dlc5.cfg
                calao-usb-a9260-c01.cfg  jtagkey.cfg              rlink.cfg
                calao-usb-a9260-c02.cfg  jtagkey-tiny.cfg         sheevaplug.cfg
                calao-usb-a9260.cfg      luminary.cfg             signalyzer.cfg
                chameleon.cfg            luminary-icdi.cfg        stm32-stick.cfg
                cortino.cfg              luminary-lm3s811.cfg     turtelizer2.cfg
                dummy.cfg                olimex-arm-usb-ocd.cfg   usbprog.cfg
                flyswatter.cfg           olimex-jtag-tiny.cfg     vsllink.cfg
                $

- `board` ... think Circuit Board, PWA, PCB, they go by many names. Board files contain initialization items that are specific to a board. They reuse target configuration files, since the same microprocessor chips are used on many boards, but support for external parts varies widely. For example, the SDRAM initialization sequence for the board, or the type of external flash and what address it uses. Any initialization sequence to enable that external flash or SDRAM should be found in the board file. Boards may also contain multiple targets: two CPUs; or a CPU and an FPGA.

                $ ls board
                arm_evaluator7t.cfg               keil_mcb1700.cfg
                at91rm9200-dk.cfg                 keil_mcb2140.cfg
                at91sam9g20-ek.cfg                linksys_nslu2.cfg
                atmel_at91sam7s-ek.cfg            logicpd_imx27.cfg
                atmel_at91sam9260-ek.cfg          mini2440.cfg
                atmel_sam3u_ek.cfg                olimex_LPC2378STK.cfg
                crossbow_tech_imote2.cfg          olimex_lpc_h2148.cfg
                csb337.cfg                        olimex_sam7_ex256.cfg
                csb732.cfg                        olimex_sam9_l9260.cfg
                digi_connectcore_wi-9c.cfg        olimex_stm32_h103.cfg
                dm355evm.cfg                      omap2420_h4.cfg
                dm365evm.cfg                      osk5912.cfg
                dm6446evm.cfg                     pic-p32mx.cfg
                eir.cfg                           propox_mmnet1001.cfg
                ek-lm3s1968.cfg                   pxa255_sst.cfg
                ek-lm3s3748.cfg                   sheevaplug.cfg
                ek-lm3s811.cfg                    stm3210e_eval.cfg
                ek-lm3s9b9x.cfg                   stm32f10x_128k_eval.cfg
                hammer.cfg                        str910-eval.cfg
                hitex_lpc2929.cfg                 telo.cfg
                hitex_stm32-performancestick.cfg  ti_beagleboard.cfg
                hitex_str9-comstick.cfg           topas910.cfg
                iar_str912_sk.cfg                 topasa900.cfg
                imx27ads.cfg                      unknown_at91sam9260.cfg
                imx27lnst.cfg                     x300t.cfg
                imx31pdk.cfg                      zy1000.cfg
                $

- `target` ... think chip. The “target” directory represents the JTAG TAPs on a chip which OpenOCD should control, not a board. Two common types of targets are ARM chips and FPGA or CPLD chips. When a chip has multiple TAPs (maybe it has both ARM and DSP cores), the target config file defines all of them.

                $ ls target
                aduc702x.cfg     imx27.cfg     pxa255.cfg
                ar71xx.cfg       imx31.cfg     pxa270.cfg
                at91eb40a.cfg    imx35.cfg     readme.txt
                at91r40008.cfg   is5114.cfg    sam7se512.cfg
                at91rm9200.cfg   ixp42x.cfg    sam7x256.cfg
                at91sam3u1c.cfg  lm3s1968.cfg  samsung_s3c2410.cfg
                at91sam3u1e.cfg  lm3s3748.cfg  samsung_s3c2440.cfg
                at91sam3u2c.cfg  lm3s6965.cfg  samsung_s3c2450.cfg
                at91sam3u2e.cfg  lm3s811.cfg   samsung_s3c4510.cfg
                at91sam3u4c.cfg  lm3s9b9x.cfg  samsung_s3c6410.cfg
                at91sam3u4e.cfg  lpc1768.cfg   sharp_lh79532.cfg
                at91sam3uXX.cfg  lpc2103.cfg   smdk6410.cfg
                at91sam7sx.cfg   lpc2124.cfg   smp8634.cfg
                at91sam9260.cfg  lpc2129.cfg   stm32.cfg
                c100.cfg         lpc2148.cfg   str710.cfg
                c100config.tcl   lpc2294.cfg   str730.cfg
                c100helper.tcl   lpc2378.cfg   str750.cfg
                c100regs.tcl     lpc2478.cfg   str912.cfg
                cs351x.cfg       lpc2900.cfg   telo.cfg
                davinci.cfg      mega128.cfg   ti_dm355.cfg
                dragonite.cfg    netx500.cfg   ti_dm365.cfg
                epc9301.cfg      omap2420.cfg  ti_dm6446.cfg
                feroceon.cfg     omap3530.cfg  tmpa900.cfg
                icepick.cfg      omap5912.cfg  tmpa910.cfg
                imx21.cfg        pic32mx.cfg   xba_revA3.cfg
                $

- more ... browse for other library files which may be useful. For example, there are various generic and CPU-specific utilities.

The `openocd.cfg` user config file may override features in any of the above files by setting variables before sourcing the target file, or by adding commands specific to their situation.

### 6.1 Interface Config Files

The user config file should be able to source one of these files with a command like this:

         source [find interface/FOOBAR.cfg]

A preconfigured interface file should exist for every debug adapter in use today with OpenOCD. That said, perhaps some of these config files have only been used by the developer who created it.

A separate chapter gives information about how to set these up. See Debug Adapter Configuration. Read the OpenOCD source code (and Developer's GUide) if you have a new kind of hardware interface and need to provide a driver for it.

### 6.2 Board Config Files

The user config file should be able to source one of these files with a command like this:

         source [find board/FOOBAR.cfg]

The point of a board config file is to package everything about a given board that user config files need to know. In summary the board files should contain (if present)

1. One or more `source [target/...cfg]` statements
2. NOR flash configuration (see NOR Configuration)
3. NAND flash configuration (see NAND Configuration)
4. Target `reset` handlers for SDRAM and I/O configuration
5. JTAG adapter reset configuration (see Reset Configuration)
6. All things that are not “inside a chip”

Generic things inside target chips belong in target config files, not board config files. So for example a `reset-init` event handler should know board-specific oscillator and PLL parameters, which it passes to target-specific utility code.

The most complex task of a board config file is creating such a `reset-init` event handler. Define those handlers last, after you verify the rest of the board configuration works.

#### 6.2.1 Communication Between Config files

In addition to target-specific utility code, another way that board and target config files communicate is by following a convention on how to use certain variables.

The full Tcl/Tk language supports “namespaces”, but JIM-Tcl does not. Thus the rule we follow in OpenOCD is this: Variables that begin with a leading underscore are temporary in nature, and can be modified and used at will within a target configuration file.

Complex board config files can do the things like this, for a board with three chips:

         # Chip #1: PXA270 for network side, big endian
         set CHIPNAME network
         set ENDIAN big
         source [find target/pxa270.cfg]
         # on return: _TARGETNAME = network.cpu
         # other commands can refer to the "network.cpu" target.
         $_TARGETNAME configure .... events for this CPU..

         # Chip #2: PXA270 for video side, little endian
         set CHIPNAME video
         set ENDIAN little
         source [find target/pxa270.cfg]
         # on return: _TARGETNAME = video.cpu
         # other commands can refer to the "video.cpu" target.
         $_TARGETNAME configure .... events for this CPU..

         # Chip #3: Xilinx FPGA for glue logic
         set CHIPNAME xilinx
         unset ENDIAN
         source [find target/spartan3.cfg]

That example is oversimplified because it doesn't show any flash memory, or the `reset-init` event handlers to initialize external DRAM or (assuming it needs it) load a configuration into the FPGA. Such features are usually needed for low-level work with many boards, where “low level” implies that the board initialization software may not be working. (That's a common reason to need JTAG tools. Another is to enable working with microcontroller-based systems, which often have no debugging support except a JTAG connector.)

Target config files may also export utility functions to board and user config files. Such functions should use name prefixes, to help avoid naming collisions.

Board files could also accept input variables from user config files. For example, there might be a `J4_JUMPER` setting used to identify what kind of flash memory a development board is using, or how to set up other clocks and peripherals.

#### 6.2.2 Variable Naming Convention

Most boards have only one instance of a chip. However, it should be easy to create a board with more than one such chip (as shown above). Accordingly, we encourage these conventions for naming variables associated with different `target.cfg` files, to promote consistency and so that board files can override target defaults.

Inputs to target config files include:

- `CHIPNAME` ... This gives a name to the overall chip, and is used as part of tap identifier dotted names. While the default is normally provided by the chip manufacturer, board files may need to distinguish between instances of a chip.
- `ENDIAN` ... By default `little` - although chips may hard-wire `big`. Chips that can't change endianness don't need to use this variable.
- `CPUTAPID` ... When OpenOCD examines the JTAG chain, it can be told verify the chips against the JTAG IDCODE register. The target file will hold one or more defaults, but sometimes the chip in a board will use a different ID (perhaps a newer revision).

Outputs from target config files include:

- `_TARGETNAME` ... By convention, this variable is created by the target configuration script. The board configuration file may make use of this variable to configure things like a “reset init” script, or other things specific to that board and that target. If the chip has 2 targets, the names are `_TARGETNAME0`, `_TARGETNAME1`, ... etc.

#### 6.2.3 The reset-init Event Handler

Board config files run in the OpenOCD configuration stage; they can't use TAPs or targets, since they haven't been fully set up yet. This means you can't write memory or access chip registers; you can't even verify that a flash chip is present. That's done later in event handlers, of which the target `reset-init` handler is one of the most important.

Except on microcontrollers, the basic job of `reset-init` event handlers is setting up flash and DRAM, as normally handled by boot loaders. Microcontrollers rarely use boot loaders; they run right out of their on-chip flash and SRAM memory. But they may want to use one of these handlers too, if just for developer convenience.

> Note: Because this is so very board-specific, and chip-specific, no examples are included here. Instead, look at the board config files distributed with OpenOCD. If you have a boot loader, its source code will help; so will configuration files for other JTAG tools (see Translating Configuration Files).

Some of this code could probably be shared between different boards. For example, setting up a DRAM controller often doesn't differ by much except the bus width (16 bits or 32?) and memory timings, so a reusable TCL procedure loaded by the `target.cfg` file might take those as parameters. Similarly with oscillator, PLL, and clock setup; and disabling the watchdog. Structure the code cleanly, and provide comments to help the next developer doing such work. (You might be that next person trying to reuse init code!)

The last thing normally done in a `reset-init` handler is probing whatever flash memory was configured. For most chips that needs to be done while the associated target is halted, either because JTAG memory access uses the CPU or to prevent conflicting CPU access.

#### 6.2.4 JTAG Clock Rate

Before your `reset-init` handler has set up the PLLs and clocking, you may need to run with a low JTAG clock rate. See JTAG Speed. Then you'd increase that rate after your handler has made it possible to use the faster JTAG clock. When the initial low speed is board-specific, for example because it depends on a board-specific oscillator speed, then you should probably set it up in the board config file; if it's target-specific, it belongs in the target config file.

For most ARM-based processors the fastest JTAG clock1 is one sixth of the CPU clock; or one eighth for ARM11 cores. Consult chip documentation to determine the peak JTAG clock rate, which might be less than that.

> Warning: On most ARMs, JTAG clock detection is coupled to the core clock, so software using a `wait for interrupt` operation blocks JTAG access. Adaptive clocking provides a partial workaround, but a more complete solution just avoids using that instruction with JTAG debuggers.

If both the chip and the board support adaptive clocking, use the `jtag_rclk` command, in case your board is used with JTAG adapter which also supports it. Otherwise use `adapter_khz`. Set the slow rate at the beginning of the reset sequence, and the faster rate as soon as the clocks are at full speed.

### 6.3 Target Config Files

Board config files communicate with target config files using naming conventions as described above, and may source one or more target config files like this:

         source [find target/FOOBAR.cfg]

The point of a target config file is to package everything about a given chip that board config files need to know. In summary the target files should contain

1. Set defaults
2. Add TAPs to the scan chain
3. Add CPU targets (includes GDB support)
4. CPU/Chip/CPU-Core specific features
5. On-Chip flash

As a rule of thumb, a target file sets up only one chip. For a microcontroller, that will often include a single TAP, which is a CPU needing a GDB target, and its on-chip flash.

More complex chips may include multiple TAPs, and the target config file may need to define them all before OpenOCD can talk to the chip. For example, some phone chips have JTAG scan chains that include an ARM core for operating system use, a DSP, another ARM core embedded in an image processing engine, and other processing engines.

#### 6.3.1 Default Value Boiler Plate Code

All target configuration files should start with code like this, letting board config files express environment-specific differences in how things should be set up.

         # Boards may override chip names, perhaps based on role,
         # but the default should match what the vendor uses
         if { [info exists CHIPNAME] } {
            set  _CHIPNAME $CHIPNAME
         } else {
            set  _CHIPNAME sam7x256
         }

         # ONLY use ENDIAN with targets that can change it.
         if { [info exists ENDIAN] } {
            set  _ENDIAN $ENDIAN
         } else {
            set  _ENDIAN little
         }

         # TAP identifiers may change as chips mature, for example with
         # new revision fields (the "3" here).  Pick a good default; you
         # can pass several such identifiers to the "jtag newtap" command.
         if { [info exists CPUTAPID ] } {
            set _CPUTAPID $CPUTAPID
         } else {
            set _CPUTAPID 0x3f0f0f0f
         }

Remember: Board config files may include multiple target config files, or the same target file multiple times (changing at least `CHIPNAME`).

Likewise, the target configuration file should define `_TARGETNAME` (or `_TARGETNAME0` etc) and use it later on when defining debug targets:

         set _TARGETNAME $_CHIPNAME.cpu
         target create $_TARGETNAME arm7tdmi -chain-position $_TARGETNAME

#### 6.3.2 Adding TAPs to the Scan Chain

After the “defaults” are set up, add the TAPs on each chip to the JTAG scan chain. See TAP Declaration, and the naming convention for taps.

In the simplest case the chip has only one TAP, probably for a CPU or FPGA. The config file for the Atmel AT91SAM7X256 looks (in part) like this:

         jtag newtap $_CHIPNAME cpu -irlen 4 -expected-id $_CPUTAPID

A board with two such at91sam7 chips would be able to source such a config file twice, with different values for `CHIPNAME`, so it adds a different TAP each time.

If there are nonzero `-expected-id` values, OpenOCD attempts to verify the actual tap id against those values. It will issue error messages if there is mismatch, which can help to pinpoint problems in OpenOCD configurations.

         JTAG tap: sam7x256.cpu tap/device found: 0x3f0f0f0f
                         (Manufacturer: 0x787, Part: 0xf0f0, Version: 0x3)
         ERROR: Tap: sam7x256.cpu - Expected id: 0x12345678, Got: 0x3f0f0f0f
         ERROR: expected: mfg: 0x33c, part: 0x2345, ver: 0x1
         ERROR:      got: mfg: 0x787, part: 0xf0f0, ver: 0x3

There are more complex examples too, with chips that have multiple TAPs. Ones worth looking at include:

- `target/omap3530.cfg` – with disabled ARM and DSP, plus a JRC to enable them
- `target/str912.cfg` – with flash, CPU, and boundary scan
- `target/ti_dm355.cfg` – with ETM, ARM, and JRC (this JRC is not currently used)

#### 6.3.3 Add CPU targets

After adding a TAP for a CPU, you should set it up so that GDB and other commands can use it. See CPU Configuration. For the at91sam7 example above, the command can look like this; note that `$_ENDIAN` is not needed, since OpenOCD defaults to little endian, and this chip doesn't support changing that.

         set _TARGETNAME $_CHIPNAME.cpu
         target create $_TARGETNAME arm7tdmi -chain-position $_TARGETNAME

Work areas are small RAM areas associated with CPU targets. They are used by OpenOCD to speed up downloads, and to download small snippets of code to program flash chips. If the chip includes a form of “on-chip-ram” - and many do - define a work area if you can. Again using the at91sam7 as an example, this can look like:

         $_TARGETNAME configure -work-area-phys 0x00200000 \
                      -work-area-size 0x4000 -work-area-backup 0

#### 6.3.4 Chip Reset Setup

As a rule, you should put the `reset_config` command into the board file. Most things you think you know about a 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 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 `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. An example might be needing to send some commands right after the target's TAP has been reset, providing a `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) are the right places to handle some of those issues. For example, immediately after reset most chips run using a slower clock than they will use later. That means that after reset (and potentially, as OpenOCD first starts up) they must use a slower JTAG clock rate than they will use later. See JTAG Speed.

> Important: When you are debugging code that runs right after chip reset, getting these issues right is critical. In particular, if you see intermittent failures when OpenOCD verifies the scan chain after reset, look at how you are setting up JTAG clocking.

#### 6.3.5 ARM Core Specific Hacks

If the chip has a DCC, enable it. If the chip is an ARM9 with some special high speed download features - enable it.

If present, the MMU, the MPU and the CACHE should be disabled.

Some ARM cores are equipped with trace support, which permits examination of the instruction and data bus activity. Trace activity is controlled through an “Embedded Trace Module” (ETM) on one of the core's scan chains. The ETM emits voluminous data through a “trace port”. (See ARM Hardware Tracing.) If you are using an external trace port, configure it in your board config file. If you are using an on-chip “Embedded Trace Buffer” (ETB), configure it in your target config file.

         etm config $_TARGETNAME 16 normal full etb
         etb config $_TARGETNAME $_CHIPNAME.etb

#### 6.3.6 Internal Flash Configuration

This applies ONLY TO MICROCONTROLLERS that have flash built in.

Never ever in the “target configuration file” define any type of flash that is external to the chip. (For example a BOOT flash on Chip Select 0.) Such flash information goes in a board file - not the TARGET (chip) file.

Examples:

- at91sam7x256 - has 256K flash YES enable it.
- str912 - has flash internal YES enable it.
- imx27 - uses boot flash on CS0 - it goes in the board file.
- pxa270 - again - CS0 flash - it goes in the board file.

### 6.4 Translating Configuration Files

If you have a configuration file for another hardware debugger or toolset (Abatron, BDI2000, BDI3000, CCS, Lauterbach, Segger, Macraigor, etc.), translating it into OpenOCD syntax is often quite straightforward. The most tricky part of creating a configuration script is oftentimes the reset init sequence where e.g. PLLs, DRAM and the like is set up.

One trick that you can use when translating is to write small Tcl procedures to translate the syntax into OpenOCD syntax. This can avoid manual translation errors and make it easier to convert other scripts later on.

Example of transforming quirky arguments to a simple search and replace job:

         #   Lauterbach syntax(?)
         #
         #       Data.Set c15:0x042f %long 0x40000015
         #
         #   OpenOCD syntax when using procedure below.
         #
         #       setc15 0x01 0x00050078

         proc setc15 {regs value} {
             global TARGETNAME

             echo [format "set p15 0x%04x, 0x%08x" $regs $value]

             arm mcr 15 [expr ($regs>>12)&0x7] \
                 [expr ($regs>>0)&0xf] [expr ($regs>>4)&0xf] \
                 [expr ($regs>>8)&0x7] $value
         }

#### Footnotes

[1] A FAQ http://www.arm.com/support/faqdev/4170.html gives details.