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 RedBoot.

Debugging of ROM applications is only possible if using hardware breakpoints. The ARM7TDMI core of the STR7XX only supports two 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. Some JTAG devices give the option of whether to set hardware or software breakpoints by default. Be sure to configure your device appropriately.

Abatron BDI2000 notes

On the Abatron BDI2000, the bdi2000.str710eval.cfg file should be used to setup and configure the hardware to an appropriate state to load programs.

The bdi2000.str710eval.cfg file also contains an option to define whether hardware or software breakpoints are used by default, using the BREAKMODE directive in the [TARGET] section. Edit this file if you wish to use software break points, and remember to use the boot command on the BDI2000 command line interface to make the changes take effect.

On the BDI2000, debugging can be performed either via the telnet interface or using arm-eabi-gdb and the bdiGDB interface. In the case of the latter, arm-eabi-gdb needs to connect to TCP port 2001 on the BDI2000's IP address. For example:

(gdb) target remote 111.222.333.444:2001

By default when the BDI2000 is powered up, the target will always run the initialization section of the bdi2000.str710eval.cfg file, and halt the target. This behaviour is repeated with the reset command.

If the board is reset when in 'reset' mode (either with the 'reset halt' or 'reset' commands, or by pressing the reset button) and the 'go' command is then given, then the board will boot as normal. If a ROM RedBoot is resident in Flash, it will be run.

It is also possible for the target to always run, without initialization, after the reset button has been pressed. This mode is selected with the reset run command. This conveniently allows the target to be connected to the JTAG debugger, and be able to reset it with the reset button, without being required to always type 'go' every time. Thereafter, invoking the reset command will repeat the previous reset style. Also in this mode, exceptions will be handled by board software, rather than causing the JTAG debugger to halt the CPU.

Suitably configured JTAG applications can be loaded either via GDB, or directly via the telnet CLI. For example:

Core#0>load 0x62000000 test.bin bin
Loading /test.bin , please wait ....
Loading program file passed
Core#0>go 0x620000000

Consult the BDI2000 documentation for information on other formats.

Configuration of JTAG applications

JTAG applications can be loaded directly into RAM without requiring a ROM monitor. This loading can be done directly through the JTAG device, or where supported by the JTAG device, through GDB.

In order to configure the application to support this mode, some configuration settings are required. Firstly CYGSEM_HAL_USE_ROM_MONITOR must be disabled. Secondly the CYGDBG_HAL_DIAG_TO_DEBUG_CHAN option should be enabled in order to prevent HAL diagnostic output being encoded into GDB ($O) packets. Both of these settings are made automatically if the JTAG startup type is selected.