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Correctly installing OpenOCD includes making your operating system give OpenOCD access to debug adapters. Once that has been done, Tcl commands are used to select which one is used, and to configure how it is used.
Note: Because OpenOCD started out with a focus purely on JTAG, you may find places where it wrongly presumes JTAG is the only transport protocol in use. Be aware that recent versions of OpenOCD are removing that limitation. JTAG remains more functional than most other transports. Other transports do not support boundary scan operations, or may be specific to a given chip vendor. Some might be usable only for programming flash memory, instead of also for debugging.
Debug Adapters/Interfaces/Dongles are normally configured through commands in an interface configuration file which is sourced by your openocd.cfg file, or through a command line -f interface/....cfg option.
source [find interface/olimex-jtag-tiny.cfg]
These commands tell OpenOCD what type of JTAG adapter you have, and how to talk to it. A few cases are so simple that you only need to say what driver to use:
# jlink interface interface jlink
Most adapters need a bit more configuration than that.
The interface command tells OpenOCD what type of debug adapter you are using. Depending on the type of adapter, you may need to use one or more additional commands to further identify or configure the adapter.
Use the interface driver name to connect to the target.
List the debug adapter drivers that have been built into the running copy of OpenOCD.
Specifies the transports supported by this debug adapter. The adapter driver builds-in similar knowledge; use this only when external configuration (such as jumpering) changes what the hardware can support.
Returns the name of the debug adapter driver being used.
Each of the interface drivers listed here must be explicitly enabled when OpenOCD is configured, in order to be made available at run time.
Amontec Chameleon in its JTAG Accelerator configuration, connected to a PC’s EPP mode parallel port. This defines some driver-specific commands:
Specifies either the address of the I/O port (default: 0x378 for LPT1) or the number of the /dev/parport device.
Displays status of RTCK option. Optionally sets that option first.
Olimex ARM-JTAG-EW USB adapter This has one driver-specific command:
Logs some status
Supports bitbanged JTAG from the local system, presuming that system is an Atmel AT91rm9200 and a specific set of GPIOs is used.
ARM CMSIS-DAP compliant based adapter.
The vendor ID and product ID of the CMSIS-DAP device. If not specified the driver will attempt to auto detect the CMSIS-DAP device. Currently, up to eight [vid, pid] pairs may be given, e.g.
cmsis_dap_vid_pid 0xc251 0xf001 0x0d28 0x0204
Display various device information, like hardware version, firmware version, current bus status.
A dummy software-only driver for debugging.
Cirrus Logic EP93xx based single-board computer bit-banging (in development)
FTDI FT2232 (USB) based devices over one of the userspace libraries.
Note that this driver has several flaws and the ftdi driver is
recommended as its replacement.
These interfaces have several commands, used to configure the driver before initializing the JTAG scan chain:
Provides the USB device description (the iProduct string) of the FTDI FT2232 device. If not specified, the FTDI default value is used. This setting is only valid if compiled with FTD2XX support.
Specifies the serial-number of the FTDI FT2232 device to use, in case the vendor provides unique IDs and more than one FT2232 device is connected to the host. If not specified, serial numbers are not considered. (Note that USB serial numbers can be arbitrary Unicode strings, and are not restricted to containing only decimal digits.)
Each vendor’s FT2232 device can use different GPIO signals to control output-enables, reset signals, and LEDs. Currently valid layout name values include:
The vendor ID and product ID of the FTDI FT2232 device. If not specified, the FTDI default values are used. Currently, up to eight [vid, pid] pairs may be given, e.g.
ft2232_vid_pid 0x0403 0xcff8 0x15ba 0x0003
On some systems using FT2232 based JTAG interfaces the FT_Read function call in ft2232_read() fails to return the expected number of bytes. This can be caused by USB communication delays and has proved hard to reproduce and debug. Setting the FT2232 latency timer to a larger value increases delays for short USB packets but it also reduces the risk of timeouts before receiving the expected number of bytes. The OpenOCD default value is 2 and for some systems a value of 10 has proved useful.
Used to select the channel of the ft2232 chip to use (between 1 and 4). The default value is 1.
For example, the interface config file for a Turtelizer JTAG Adapter looks something like this:
interface ft2232 ft2232_device_desc "Turtelizer JTAG/RS232 Adapter" ft2232_layout turtelizer2 ft2232_vid_pid 0x0403 0xbdc8
This driver is for adapters using the MPSSE (Multi-Protocol Synchronous Serial Engine) mode built into many FTDI chips, such as the FT2232, FT4232 and FT232H. It is a complete rewrite to address a large number of problems with the ft2232 interface driver.
The driver is using libusb-1.0 in asynchronous mode to talk to the FTDI device, bypassing intermediate libraries like libftdi of D2XX. Performance-wise it is consistently faster than the ft2232 driver, sometimes several times faster.
A major improvement of this driver is that support for new FTDI based adapters can be added competely through configuration files, without the need to patch and rebuild OpenOCD.
The driver uses a signal abstraction to enable Tcl configuration files to
define outputs for one or several FTDI GPIO. These outputs can then be
controlled using the ftdi_set_signal command. Special signal names
are reserved for nTRST, nSRST and LED (for blink) so that they, if defined,
will be used for their customary purpose.
Depending on the type of buffer attached to the FTDI GPIO, the outputs have to be controlled differently. In order to support tristateable signals such as nSRST, both a data GPIO and an output-enable GPIO can be specified for each signal. The following output buffer configurations are supported:
These interfaces have several commands, used to configure the driver before initializing the JTAG scan chain:
The vendor ID and product ID of the adapter. If not specified, the FTDI default values are used. Currently, up to eight [vid, pid] pairs may be given, e.g.
ftdi_vid_pid 0x0403 0xcff8 0x15ba 0x0003
Provides the USB device description (the iProduct string) of the adapter. If not specified, the device description is ignored during device selection.
Specifies the serial-number of the adapter to use, in case the vendor provides unique IDs and more than one adapter is connected to the host. If not specified, serial numbers are not considered. (Note that USB serial numbers can be arbitrary Unicode strings, and are not restricted to containing only decimal digits.)
Selects the channel of the FTDI device to use for MPSSE operations. Most adapters use the default, channel 0, but there are exceptions.
Specifies the initial values of the FTDI GPIO data and direction registers. Each value is a 16-bit number corresponding to the concatenation of the high and low FTDI GPIO registers. The values should be selected based on the schematics of the adapter, such that all signals are set to safe levels with minimal impact on the target system. Avoid floating inputs, conflicting outputs and initially asserted reset signals.
Creates a signal with the specified name, controlled by one or more FTDI GPIO pins via a range of possible buffer connections. The masks are FTDI GPIO register bitmasks to tell the driver the connection and type of the output buffer driving the respective signal. data_mask is the bitmask for the pin(s) connected to the data input of the output buffer. -ndata is used with inverting data inputs and -data with non-inverting inputs. The -oe (or -noe) option tells where the output-enable (or not-output-enable) input to the output buffer is connected.
Both data_mask and oe_mask need not be specified. For example, a
simple open-collector transistor driver would be specified with -oe
only. In that case the signal can only be set to drive low or to Hi-Z and the
driver will complain if the signal is set to drive high. Which means that if
it’s a reset signal, reset_config must be specified as
srst_open_drain, not srst_push_pull.
A special case is provided when -data and -oe is set to the same bitmask. Then the FTDI pin is considered being connected straight to the target without any buffer. The FTDI pin is then switched between output and input as necessary to provide the full set of low, high and Hi-Z characteristics. In all other cases, the pins specified in a signal definition are always driven by the FTDI.
Set a previously defined signal to the specified level.
For example adapter definitions, see the configuration files shipped in the interface/ftdi directory.
Drive JTAG from a remote process. This sets up a UNIX or TCP socket connection with a remote process and sends ASCII encoded bitbang requests to that process instead of directly driving JTAG.
The remote_bitbang driver is useful for debugging software running on processors which are being simulated.
Specifies the TCP port of the remote process to connect to or 0 to use UNIX sockets instead of TCP.
Specifies the hostname of the remote process to connect to using TCP, or the name of the UNIX socket to use if remote_bitbang_port is 0.
For example, to connect remotely via TCP to the host foobar you might have something like:
interface remote_bitbang remote_bitbang_port 3335 remote_bitbang_host foobar
To connect to another process running locally via UNIX sockets with socket named mysocket:
interface remote_bitbang remote_bitbang_port 0 remote_bitbang_host mysocket
USB JTAG/USB-Blaster compatibles over one of the userspace libraries for FTDI chips. These interfaces have several commands, used to configure the driver before initializing the JTAG scan chain:
Provides the USB device description (the iProduct string) of the FTDI FT245 device. If not specified, the FTDI default value is used. This setting is only valid if compiled with FTD2XX support.
The vendor ID and product ID of the FTDI FT245 device. If not specified, default values are used. Currently, only one vid, pid pair may be given, e.g. for Altera USB-Blaster (default):
usb_blaster_vid_pid 0x09FB 0x6001
The following VID/PID is for Kolja Waschk’s USB JTAG:
usb_blaster_vid_pid 0x16C0 0x06AD
Sets the state of the unused GPIO pins on USB-Blasters (pins 6 and 8 on the female JTAG header). These pins can be used as SRST and/or TRST provided the appropriate connections are made on the target board.
For example, to use pin 6 as SRST (as with an AVR board):
$_TARGETNAME configure -event reset-assert \
"usb_blaster pin6 1; wait 1; usb_blaster pin6 0"
Gateworks GW16012 JTAG programmer. This has one driver-specific command:
Display either the address of the I/O port (default: 0x378 for LPT1) or the number of the /dev/parport device. If a parameter is provided, first switch to use that port. This is a write-once setting.
Segger J-Link family of USB adapters. It currently supports only the JTAG transport.
Compatibility Note: Segger released many firmware versions for the many harware versions they produced. OpenOCD was extensively tested and intended to run on all of them, but some combinations were reported as incompatible. As a general recommendation, it is advisable to use the latest firmware version available for each hardware version. However the current V8 is a moving target, and Segger firmware versions released after the OpenOCD was released may not be compatible. In such cases it is recommended to revert to the last known functional version. For 0.5.0, this is from "Feb 8 2012 14:30:39", packed with 4.42c. For 0.6.0, the last known version is from "May 3 2012 18:36:22", packed with 4.46f.
Display the device firmware capabilities.
Display various device information, like hardware version, firmware version, current bus status.
Set the JTAG protocol version to be used. Without argument, show the actual JTAG protocol version.
Display the J-Link configuration.
Set the Kickstart power on JTAG-pin 19. Without argument, show the Kickstart configuration.
Set the MAC address of the J-Link Pro. Without argument, show the MAC address.
Set the IP configuration of the J-Link Pro, where A.B.C.D is the IP address, E the bit of the subnet mask and F.G.H.I the subnet mask. Without arguments, show the IP configuration.
Set the USB address; this will also change the product id. Without argument, show the USB address.
Reset the current configuration.
Save the current configuration to the internal persistent storage.
Set the USB PID of the interface. As a configuration command, it can be used only before ’init’.
Supports PC parallel port bit-banging cables: Wigglers, PLD download cable, and more. These interfaces have several commands, used to configure the driver before initializing the JTAG scan chain:
Set the layout of the parallel port cable used to connect to the target. This is a write-once setting. Currently valid cable name values include:
Display either the address of the I/O port (default: 0x378 for LPT1) or the number of the /dev/parport device. If a parameter is provided, first switch to use that port. This is a write-once setting.
When using PPDEV to access the parallel port, use the number of the parallel port: parport_port 0 (the default). If parport_port 0x378 is specified you may encounter a problem.
Displays how many nanoseconds the hardware needs to toggle TCK;
the parport driver uses this value to obey the
adapter_khz configuration.
When the optional nanoseconds parameter is given,
that setting is changed before displaying the current value.
The default setting should work reasonably well on commodity PC hardware. However, you may want to calibrate for your specific hardware.
Tip: To measure the toggling time with a logic analyzer or a digital storage oscilloscope, follow the procedure below:
> parport_toggling_time 1000 > adapter_khz 500This sets the maximum JTAG clock speed of the hardware, but the actual speed probably deviates from the requested 500 kHz. Now, measure the time between the two closest spaced TCK transitions. You can use
runtest 1000or something similar to generate a large set of samples. Update the setting to match your measurement:> parport_toggling_time <measured nanoseconds>Now the clock speed will be a better match for
adapter_khz ratecommands given in OpenOCD scripts and event handlers.You can do something similar with many digital multimeters, but note that you’ll probably need to run the clock continuously for several seconds before it decides what clock rate to show. Adjust the toggling time up or down until the measured clock rate is a good match for the adapter_khz rate you specified; be conservative.
This will configure the parallel driver to write a known cable-specific value to the parallel interface on exiting OpenOCD.
For example, the interface configuration file for a classic “Wiggler” cable on LPT2 might look something like this:
interface parport parport_port 0x278 parport_cable wiggler
ASIX PRESTO USB JTAG programmer.
Configures the USB serial number of the Presto device to use.
Raisonance RLink USB adapter
usbprog is a freely programmable USB adapter.
vsllink is part of Versaloon which is a versatile USB programmer.
Note: This defines quite a few driver-specific commands, which are not currently documented here.
This is a driver that supports multiple High Level Adapters. This type of adapter does not expose some of the lower level api’s that OpenOCD would normally use to access the target.
Currently supported adapters include the ST STLINK and TI ICDI.
Currently Not Supported.
Currently Not Supported.
Specifies the adapter layout to use.
The vendor ID and product ID of the device.
Enable SWO tracing (if supported). The source clock rate for the trace port must be specified, this is typically the CPU clock rate. If the optional output file is specified then raw trace data is appended to the file, and the file is created if it does not exist.
opendous-jtag is a freely programmable USB adapter.
This is the Keil ULINK v1 JTAG debugger.
This is the Zylin ZY1000 JTAG debugger.
Note: This defines some driver-specific commands, which are not currently documented here.
Turn power switch to target on/off. No arguments: print status.
This SoC is present in Raspberry Pi which is a cheap single-board computer exposing some GPIOs on its expansion header.
The driver accesses memory-mapped GPIO peripheral registers directly for maximum performance, but the only possible race condition is for the pins’ modes/muxing (which is highly unlikely), so it should be able to coexist nicely with both sysfs bitbanging and various peripherals’ kernel drivers. The driver restores the previous configuration on exit.
See interface/raspberrypi-native.cfg for a sample config and pinout.
As noted earlier, depending on the version of OpenOCD you use, and the debug adapter you are using, several transports may be available to communicate with debug targets (or perhaps to program flash memory).
displays the names of the transports supported by this version of OpenOCD.
Select which of the supported transports to use in this OpenOCD session. The transport must be supported by the debug adapter hardware and by the version of OpenOCD you are using (including the adapter’s driver). No arguments: returns name of session’s selected transport.
JTAG is the original transport supported by OpenOCD, and most of the OpenOCD commands support it. JTAG transports expose a chain of one or more Test Access Points (TAPs), each of which must be explicitly declared. JTAG supports both debugging and boundary scan testing. Flash programming support is built on top of debug support.
SWD (Serial Wire Debug) is an ARM-specific transport which exposes one Debug Access Point (DAP, which must be explicitly declared. (SWD uses fewer signal wires than JTAG.) SWD is debug-oriented, and does not support boundary scan testing. Flash programming support is built on top of debug support. (Some processors support both JTAG and SWD.)
Declares a single DAP which uses SWD transport. Parameters are currently the same as "jtag newtap" but this is expected to change.
Updates TRN (turnaraound delay) and prescaling.fields of the Wire Control Register (WCR). No parameters: displays current settings.
CMSIS-DAP is an ARM-specific transport that is used to connect to compilant debuggers.
The Serial Peripheral Interface (SPI) is a general purpose transport which uses four wire signaling. Some processors use it as part of a solution for flash programming.
JTAG clock setup is part of system setup. It does not belong with interface setup since any interface only knows a few of the constraints for the JTAG clock speed. Sometimes the JTAG speed is changed during the target initialization process: (1) slow at reset, (2) program the CPU clocks, (3) run fast. Both the "slow" and "fast" clock rates are functions of the oscillators used, the chip, the board design, and sometimes power management software that may be active.
The speed used during reset, and the scan chain verification which
follows reset, can be adjusted using a reset-start
target event handler.
It can then be reconfigured to a faster speed by a
reset-init target event handler after it reprograms those
CPU clocks, or manually (if something else, such as a boot loader,
sets up those clocks).
See Target Events.
When the initial low JTAG speed is a chip characteristic, perhaps
because of a required oscillator speed, provide such a handler
in the target config file.
When that speed is a function of a board-specific characteristic
such as which speed oscillator is used, it belongs in the board
config file instead.
In both cases it’s safest to also set the initial JTAG clock rate
to that same slow speed, so that OpenOCD never starts up using a
clock speed that’s faster than the scan chain can support.
jtag_rclk 3000
$_TARGET.cpu configure -event reset-start { jtag_rclk 3000 }
If your system supports adaptive clocking (RTCK), configuring JTAG to use that is probably the most robust approach. However, it introduces delays to synchronize clocks; so it may not be the fastest solution.
NOTE: Script writers should consider using jtag_rclk
instead of adapter_khz, but only for (ARM) cores and boards
which support adaptive clocking.
A non-zero speed is in KHZ. Hence: 3000 is 3mhz. JTAG interfaces usually support a limited number of speeds. The speed actually used won’t be faster than the speed specified.
Chip data sheets generally include a top JTAG clock rate. The actual rate is often a function of a CPU core clock, and is normally less than that peak rate. For example, most ARM cores accept at most one sixth of the CPU clock.
Speed 0 (khz) selects RTCK method. See FAQ RTCK. If your system uses RTCK, you won’t need to change the JTAG clocking after setup. Not all interfaces, boards, or targets support “rtck”. If the interface device can not support it, an error is returned when you try to use RTCK.
This Tcl proc (defined in startup.tcl) attempts to enable RTCK/RCLK. If that fails (maybe the interface, board, or target doesn’t support it), falls back to the specified frequency.
# Fall back to 3mhz if RTCK is not supported jtag_rclk 3000
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