JTAG support — Usage

Use of JTAG for debugging

JTAG can be used to single-step and debug loaded applications, or even applications resident in ROM, including the GDB stub ROM.

Debugging of ROM applications is only possible if using hardware breakpoints. The Cortex-M3 core of the STM32 only supports six such hardware breakpoints, so they should be used sparingly. If using a GDB front-end such as Eclipse, check it has not set unnecessary extra breakpoints such as at main(). Some JTAG devices give the option of whether to set hardware or software breakpoints by default. Be sure to configure your device appropriately.

The base BCM943364WCD1 module exposes the STM32F411RE JTAG/SWD signals on the module connectors TP7..TP11. A suitable hardware connection would be required to allow JTAG debugging. The BCM943364WCD1_EVB kit provides a standard 20-pin ARM JTAG header J3, but by default the module JTAG connection is configured to use the BCM9WCD9EVAL1 motherboard FT2232 connection presented via the USB J4 connector. Direct support for this USB interface is provided by the WICED-SDK supplied OpenOCD binary.

When debugging via JTAG, you are likely to need to disable the default HAL idle thread action, otherwise there may be issues where the target fails to halt and the debugging session is unreliable. More details can be found in the Cortex-M architectural HAL.

Normally a notable disadvantage with JTAG debugging is that it does not allow thread-aware debugging, such as the ability to inspect different eCos threads or their stack backtraces, set thread-specific breakpoints, and so on. Fortunately the Ronetix PEEDI JTAG unit does support thread-aware debugging of eCos applications, however extra configuration steps are required. Consult the PEEDI documentation for more details as usage is beyond the scope of this document.

OpenOCD notes

The following OpenOCD documentation uses as an example the BCM943364WCD1_EVB J4 USB JTAG connection. An OpenOCD configuration that supports the ft2232 interface and understands the ft2232_layout BCM9WCD1EVAL1 configuration must be used, Such an openocd is pre-built and available in the WICED-SDK. For example WICED-SDK revision 3.5.1 the necessary host binaries can be found in the directory WICED-SDK-3.5.1/tools/OpenOCD.

An example OpenOCD configuration file openocd.bcm943364wcd1_evb.cfg is provided within the eCos platform HAL package in the source repository. This will be in the directory packages/hal/cortexm/stm32/bcm943364wcd1/VERSION/misc relative to the root of your eCos installation.

This configuration file can be used with the WICED-SDK supplied OpenOCD on the host as follows:

$ ./Linux64/openocd-all-brcm-libftdi -f openocd.bcm943364wcd1_evb.cfg
Open On-Chip Debugger 0.9.0-00029-g33ca6ac-dirty (2015-05-28-14:31)
Licensed under GNU GPL v2
For bug reports, read
Info : only one transport option; autoselect 'jtag'
trst_and_srst separate srst_nogate trst_push_pull srst_push_pull connect_assert_srst
adapter speed: 2000 kHz
adapter_nsrst_delay: 100
jtag_ntrst_delay: 100
cortex_m reset_config sysresetreq
Warn : Using DEPRECATED interface driver 'ft2232'
Info : Consider using the 'ftdi' interface driver, with configuration files in interface/ftdi/...
Info : max TCK change to: 30000 kHz
Info : clock speed 2000 kHz
Info : JTAG tap: stm32f4x.cpu tap/device found: 0x4ba00477 (mfg: 0x23b, part: 0xba00, ver: 0x4)
Info : JTAG tap: tap/device found: 0x06431041 (mfg: 0x020, part: 0x6431, ver: 0x0)
Info : stm32f4x.cpu: hardware has 6 breakpoints, 4 watchpoints

By default openocd provides a console on port 4444, and this can be used to interact with the target system. This console interface can be used to perform debugging, program the flash, etc.

Normally arm-eabi-gdb is used to connect to the default GDB server port 3333 for debugging. For example:

(gdb) target remote localhost:3333
Remote debugging using localhost:3333
0x00000000 in ?? ()

The application can then be loaded and executed under GDB as normal. If you are using Eclipse then, if required, you can define a “preload” gdb macro to emit any necessary commands to OpenOCD. See the “Hardware Assisted Debugging” section of the “Eclipse/CDT for eCos application development” document's “Debugging eCos applications” chapter.