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

[Chris Johns]

And me. Thanks.

Chris

On 30/3/21 7:47 am, Gedare Bloom wrote:
> 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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