[PATCH rtems-docs v2] User/BSPs/Beagle: Add JTAG debugger section

[Gedare Bloom]

looks fine to me

On Mon, Mar 29, 2021 at 1:12 PM Christian Mauderer <oss at c-mauderer.de> wrote:
>
> ---
>  user/bsps/arm/beagle.rst | 67 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 65 insertions(+), 2 deletions(-)
>
> diff --git a/user/bsps/arm/beagle.rst b/user/bsps/arm/beagle.rst
> index ac49b1c..5789bb8 100644
> --- a/user/bsps/arm/beagle.rst
> +++ b/user/bsps/arm/beagle.rst
> @@ -102,8 +102,8 @@ The function prototype is given below:
>         rtems_vector_number irq
>      );
>
> -Debugging
> ----------
> +Debugging using libdebugger
> +---------------------------
>
>  RTEMS's ``libdebugger`` requires the ARM debug resources be enabled for it to
>  work. The TI SOC used on the ``beagleboneblack`` board provides no access for
> @@ -162,3 +162,66 @@ If ``libdebugger`` fails to detect the registers open the ``bspdebug.c``
>  source and change ``has_tdo`` to ``1``, save then rebuild and install the
>  BSP. This will turn on an internal feeback to check the JTAG logic. Discard
>  the edit once the hardware is working.
> +
> +Debugging Beagle Bone Black using a JTAG debugger and gdb
> +---------------------------------------------------------
> +
> +Debugging a Beagle Bone Black (or variants) is also possible using a hardware
> +JTAG debugger. The JTAG is available via P2. The footprint is for an ARM 20 pin
> +cTI connector. That connector should be used, if it is necessary to have access
> +to commercially available adapters.
> +
> +For hand-made cables and adapters a standard 1.27mm pitch header and a 0.635mm
> +ribbon cable can be much cheaper. But note that even if it looks compatible,
> +it's not the same pin out as a ARM Cortex 20 pin connector!
> +
> +A lot of JTAG adapters that are working together with OpenOCD will work. There
> +are also commercially available systems (like Segger J-Link) that work well with
> +the Beagle. Note that the JTAG debugger has to be compatible with ARM Cortex A8.
> +Cortex M only debuggers (like the Segger J-Link Edu Mini) won't work.
> +
> +If the debugger offers a gdb server (like OpenOCD or Segger J-Link) the
> +following gdb start script can be used:
> +
> +.. code-block::
> +
> +    define reset
> +            echo -- Reset target and wait for U-Boot to start kernel.\n
> +            monitor reset
> +            # RTEMS U-Boot starts at this address.
> +            tbreak *0x80000000
> +            # Linux starts here.
> +            tbreak *0x82000000
> +            continue
> +
> +            echo -- Disable watchdog.\n
> +            set *(uint32_t*)0x44e35048=0xAAAA
> +            while (*(uint32_t*)0x44e35034 != 0)
> +            end
> +            set *(uint32_t*)0x44e35048=0x5555
> +            while (*(uint32_t*)0x44e35034 != 0)
> +            end
> +
> +            echo -- Overwrite kernel with application to debug.\n
> +            load
> +    end
> +
> +    target remote :2331
> +
> +Note that you might have to replace the ``monitor reset`` by some other command
> +that resets the target using your specific debugger. You also have to replace
> +the ``target remote :2331`` to match the port of your gdb server.
> +
> +The script expects that the Beagle Bone Black starts some application from an SD
> +card or from eMMC. It defines a ``reset`` command that does the following:
> +
> + * reset the target
> + * let U-Boot run, initialize the base system, load an FDT and an application
> + * break at the application entry point
> + * disable the watchdog
> + * overwrite the application that has been loaded by U-Boot with the application
> +   provided as an command line argument to gdb
> +
> +This method has the advantage that the application is executed in nearly the
> +same environment like it would be executed if loaded by U-Boot directly (except
> +for the watchdog).
> --
> 2.30.2
>
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