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doc: board: ti: k3: Add a guide to debugging with OpenOCD

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Bootloader debug usually tends to be a bit dicey prior to DDR and
serial port getting active in the system. JTAG typically remains the
only practical debug option during the initial bringup.

OpenOCD is one of the most popular environment for providing debug
capability via a GDB compatible interface for developers to work with.

Debugging U-Boot and bootloaders on K3 platform does have a bit of
tribal knowledge that is better documented in our common platform
documentation.

Signed-off-by: Jason Kacines <j-kacines@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
This commit is contained in:
Jason Kacines 2023-08-03 01:29:22 -05:00 committed by Heinrich Schuchardt
parent ef8336e270
commit effe50854a
6 changed files with 1190 additions and 0 deletions
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24
doc/board/ti/am62x_sk.rst
View file

@ -246,3 +246,27 @@ https://www.ti.com/lit/pdf/spruiv7 under the `Boot Mode Pins` section.
- 11001010
For SW2 and SW1, the switch state in the "ON" position = 1.
Debugging U-Boot
----------------
See :ref:`Common Debugging environment - OpenOCD<k3_rst_refer_openocd>`: for
detailed setup information.
.. warning::
**OpenOCD support since**: v0.12.0
If the default package version of OpenOCD in your development
environment's distribution needs to be updated, it might be necessary to
build OpenOCD from the source.
.. include:: k3.rst
:start-after: .. k3_rst_include_start_openocd_connect_XDS110
:end-before: .. k3_rst_include_end_openocd_connect_XDS110
To start OpenOCD and connect to the board
.. code-block:: bash
openocd -f board/ti_am625evm.cfg

24
doc/board/ti/am65x_evm.rst
View file

@ -287,3 +287,27 @@ artifacts needed to the device:
sb --ymodem tispl.bin > $MAIN_DEV < $MAIN_DEV
sleep 1
sb --xmodem u-boot.img > $MAIN_DEV < $MAIN_DEV
Debugging U-Boot
----------------
See :ref:`Common Debugging environment - OpenOCD<k3_rst_refer_openocd>`: for
detailed setup information.
.. warning::
**OpenOCD support since**: v0.12.0
If the default package version of OpenOCD in your development
environment's distribution needs to be updated, it might be necessary to
build OpenOCD from the source.
.. include:: k3.rst
:start-after: .. k3_rst_include_start_openocd_connect_XDS110
:end-before: .. k3_rst_include_end_openocd_connect_XDS110
To start OpenOCD and connect to the board
.. code-block:: bash
openocd -f board/ti_am654evm.cfg

580
doc/board/ti/img/openocd-overview.svg Normal file
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24
doc/board/ti/j7200_evm.rst
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@ -201,3 +201,27 @@ fat formatted UDA FS as file.
In case of booting from eMMC, write above images into raw or UDA FS.
and set mmc partconf accordingly.
Debugging U-Boot
----------------
See :ref:`Common Debugging environment - OpenOCD<k3_rst_refer_openocd>`: for
detailed setup information.
.. warning::
**OpenOCD support since**: v0.12.0
If the default package version of OpenOCD in your development
environment's distribution needs to be updated, it might be necessary to
build OpenOCD from the source.
.. include:: k3.rst
:start-after: .. k3_rst_include_start_openocd_connect_XDS110
:end-before: .. k3_rst_include_end_openocd_connect_XDS110
To start OpenOCD and connect to the board
.. code-block:: bash
openocd -f board/ti_j7200evm.cfg

24
doc/board/ti/j721e_evm.rst
View file

@ -228,3 +228,27 @@ J721E common processor board can be attached to a Ethernet QSGMII card and the
PHY in the card has to be reset before it can be used for data transfer.
"do_main_cpsw0_qsgmii_phyinit" env variable has to be set for the U-BOOT to
configure this PHY.
Debugging U-Boot
----------------
See :ref:`Common Debugging environment - OpenOCD<k3_rst_refer_openocd>`: for
detailed setup information.
.. warning::
**OpenOCD support since**: v0.12.0
If the default package version of OpenOCD in your development
environment's distribution needs to be updated, it might be necessary to
build OpenOCD from the source.
.. include:: k3.rst
:start-after: .. k3_rst_include_start_openocd_connect_XDS110
:end-before: .. k3_rst_include_end_openocd_connect_XDS110
To start OpenOCD and connect to the board
.. code-block:: bash
openocd -f board/ti_j721eevm.cfg

514
doc/board/ti/k3.rst
View file

@ -468,3 +468,517 @@ filesystem and then imported
=> fatload mmc ${mmcdev} ${loadaddr} ${bootenvfile}
=> env import -t ${loadaddr} ${filesize}
.. _k3_rst_refer_openocd:
Common Debugging environment - OpenOCD
--------------------------------------
This section will show you how to connect a board to `OpenOCD
<https://openocd.org/>`_ and load the SPL symbols for debugging with
a K3 generation device. To follow this guide, you must build custom
u-boot binaries, start your board from a boot media such as an SD
card, and use an OpenOCD environment. This section uses generic
examples, though you can apply these instructions to any supported K3
generation device.
The overall structure of this setup is in the following figure.
.. image:: img/openocd-overview.svg
.. note::
If you find these instructions useful, please consider `donating
<https://openocd.org/pages/donations.html>`_ to OpenOCD.
Step 1: Download and install OpenOCD
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
To get started, it is more convenient if the distribution you
use supports OpenOCD by default. Follow the instructions in the
`getting OpenOCD <https://openocd.org/pages/getting-openocd.html>`_
documentation to pick the installation steps appropriate to your
environment. Some references to OpenOCD documentation:
* `OpenOCD User Guide <https://openocd.org/doc/html/index.html>`_
* `OpenOCD Developer's Guide <https://openocd.org/doc/doxygen/html/index.html>`_
Refer to the release notes corresponding to the `OpenOCD version
<https://github.com/openocd-org/openocd/releases>`_ to ensure
* Processor support: In general, processor support shouldn't present
any difficulties since OpenOCD provides solid support for both ARMv8
and ARMv7.
* SoC support: When working with System-on-a-Chip (SoC), the support
usually comes as a TCL config file. It is vital to ensure the correct
version of OpenOCD or to use the TCL files from the latest release or
the one mentioned.
* Board or the JTAG adapter support: In most cases, board support is
a relatively easy problem if the board has a JTAG pin header. All
you need to do is ensure that the adapter you select is compatible
with OpenOCD. Some boards come with an onboard JTAG adapter that
requires a USB cable to be plugged into the board, in which case, it
is vital to ensure that the JTAG adapter is supported. Fortunately,
almost all TI K3 SK/EVMs come with TI's XDS110, which has out of the
box support by OpenOCD. The board-specific documentation will
cover the details and any adapter/dongle recommendations.
.. code-block:: bash
openocd -v
.. note::
OpenOCD version 0.12.0 is usually required to connect to most K3
devices. If your device is only supported by a newer version than the
one provided by your distribution, you may need to build it from the source.
Building OpenOCD from source
""""""""""""""""""""""""""""
The dependency package installation instructions below are for Debian
systems, but equivalent instructions should exist for systems with
other package managers. Please refer to the `OpenOCD Documentation
<https://openocd.org/>`_ for more recent installation steps.
.. code-block:: bash
$ # Check the packages to be installed: needs deb-src in sources.list
$ sudo apt build-dep openocd
$ # The following list is NOT complete - please check the latest
$ sudo apt-get install libtool pkg-config texinfo libusb-dev \
libusb-1.0.0-dev libftdi-dev libhidapi-dev autoconf automake
$ git clone https://github.com/openocd-org/openocd.git openocd
$ cd openocd
$ git submodule init
$ git submodule update
$ ./bootstrap
$ ./configure --prefix=/usr/local/
$ make -j`nproc`
$ sudo make install
.. note::
The example above uses the GitHub mirror site. See
`git repo information <https://openocd.org/doc/html/Developers.html#OpenOCD-Git-Repository>`_
information to pick the official git repo.
If a specific version is desired, select the version using `git checkout tag`.
Installing OpenOCD udev rules
"""""""""""""""""""""""""""""
The step is not necessary if the distribution supports the OpenOCD, but
if building from a source, ensure that the udev rules are installed
correctly to ensure a sane system.
.. code-block:: bash
# Go to the OpenOCD source directory
$ cd openocd
# Copy the udev rules to the correct system location
$ sudo cp ./contrib/60-openocd.rules \
./src/JTAG/drivers/libjaylink/contrib/99-libjaylink.rules \
/etc/udev/rules.d/
# Get Udev to load the new rules up
$ sudo udevadm control --reload-rules
# Use the new rules on existing connected devices
$ sudo udevadm trigger
Step 2: Setup GDB
^^^^^^^^^^^^^^^^^
Most systems come with gdb-multiarch package.
.. code-block:: bash
# Install gdb-multiarch package
$ sudo apt-get install gdb-multiarch
Though using GDB natively is normal, developers with interest in using IDE
may find a few of these interesting:
* `gdb-dashboard <https://github.com/cyrus-and/gdb-dashboard>`_
* `gef <https://github.com/hugsy/gef>`_
* `peda <https://github.com/longld/peda>`_
* `pwndbg <https://github.com/pwndbg/pwndbg>`_
* `voltron <https://github.com/snare/voltron>`_
* `ddd <https://www.gnu.org/software/ddd/>`_
* `vscode <https://www.justinmklam.com/posts/2017/10/vscode-debugger-setup/>`_
* `vim conque-gdb <https://github.com/vim-scripts/Conque-GDB>`_
* `emacs realgud <https://github.com/realgud/realgud/wiki/gdb-notes>`_
* `Lauterbach IDE <https://www2.lauterbach.com/pdf/backend_gdb.pdf>`_
.. warning::
LLDB support for OpenOCD is still a work in progress as of this writing.
Using GDB is probably the safest option at this point in time.
Step 3: Connect board to PC
^^^^^^^^^^^^^^^^^^^^^^^^^^^
There are few patterns of boards in the ecosystem
.. k3_rst_include_start_openocd_connect_XDS110
**Integrated JTAG adapter/dongle**: The board has a micro-USB connector labelled
XDS110 USB or JTAG. Connect a USB cable to the board to the mentioned port.
.. note::
There are multiple USB ports on a typical board, So, ensure you have read
the user guide for the board and confirmed the silk screen label to ensure
connecting to the correct port.
.. k3_rst_include_end_openocd_connect_XDS110
.. k3_rst_include_start_openocd_connect_cti20
**cTI20 connector**: The TI's `cTI20
<https://software-dl.ti.com/ccs/esd/documents/xdsdebugprobes/emu_JTAG_connectors.html#cti-20-pin-header-information>`_ connector
is probably the most prevelant on TI platforms. Though many
TI boards have an onboard XDS110, cTI20 connector is usually
provided as an alternate scheme to connect alternatives such
as `Lauterbach <https://www.lauterbach.com/>`_ or `XDS560
<https://www.ti.com/tool/TMDSEMU560V2STM-U>`_.
To debug on these boards, the following combinations is suggested:
* `TUMPA <https://www.diygadget.com/JTAG-cables-and-microcontroller-programmers/tiao-usb-multi-protocol-adapter-JTAG-spi-i2c-serial>`_
or `equivalent dongles supported by OpenOCD. <https://openocd.org/doc/html/Debug-Adapter-Hardware.html#Debug-Adapter-Hardware>`_
* Cable such as `Tag-connect ribbon cable <https://www.tag-connect.com/product/20-pin-cortex-ribbon-cable-4-length-with-50-mil-connectors>`_
* Adapter to convert cTI20 to ARM20 such as those from
`Segger <https://www.segger.com/products/debug-probes/j-link/accessories/adapters/ti-cti-20-adapter/>`_
or `Lauterbach LA-3780 <https://www.lauterbach.com/ad3780.html>`_
Or optionally, if you have manufacturing capability then you could try
`BeagleBone JTAG Adapter <https://github.com/mmorawiec/BeagleBone-Black-JTAG-Adapters>`_
.. warning::
XDS560 and Lauterbach are proprietary solutions and is not supported by
OpenOCD.
When purchasing an off the shelf adapter/dongle, you do want to be careful
about the signalling though. Please
`read for additional info <https://software-dl.ti.com/ccs/esd/xdsdebugprobes/emu_JTAG_connectors.html>`_.
.. k3_rst_include_end_openocd_connect_cti20
.. k3_rst_include_start_openocd_connect_tag_connect
**Tag-Connect**: `Tag-Connect <https://www.tag-connect.com/>`_
pads on the boards which require special cable. Please check the documentation
to `identify <https://www.tag-connect.com/info/legs-or-no-legs>`_ if "legged"
or "no-leg" version of the cable is appropriate for the board.
To debug on these boards, you will need:
* `TUMPA <https://www.diygadget.com/JTAG-cables-and-microcontroller-programmers/tiao-usb-multi-protocol-adapter-JTAG-spi-i2c-serial>`_
or `equivalent dongles supported by OpenOCD <https://openocd.org/doc/html/Debug-Adapter-Hardware.html#Debug-Adapter-Hardware>`_.
* Tag-Connect cable appropriate to the board such as
`TC2050-IDC-NL <https://www.tag-connect.com/product/TC2050-IDC-NL-10-pin-no-legs-cable-with-ribbon-connector>`_
* In case of no-leg, version, a
`retaining clip <https://www.tag-connect.com/product/tc2050-clip-3pack-retaining-clip>`_
* Tag-Connect to ARM20
`adapter <https://www.tag-connect.com/product/tc2050-arm2010-arm-20-pin-to-tc2050-adapter>`_
.. note::
You can optionally use a 3d printed solution such as
`Protective cap <https://www.thingiverse.com/thing:3025584>`_ or
`clip <https://www.thingiverse.com/thing:3035278>`_ to replace
the retaining clip.
.. warning::
With the Tag-Connect to ARM20 adapter, Please solder the "Trst" signal for
connection to work.
.. k3_rst_include_end_openocd_connect_tag_connect
Debugging with OpenOCD
^^^^^^^^^^^^^^^^^^^^^^
Debugging U-Boot is different from debugging regular user space
applications. The bootloader initialization process involves many boot
media and hardware configuration operations. For K3 devices, there
are also interactions with security firmware. While reloading the
"elf" file works through GDB, developers must be mindful of cascading
initialization's potential consequences.
Consider the following code change:
.. code-block:: diff
--- a/file.c 2023-07-29 10:55:29.647928811 -0500
+++ b/file.c 2023-07-29 10:55:46.091856816 -0500
@@ -1,3 +1,3 @@
val = readl(reg);
-val |= 0x2;
+val |= 0x1;
writel(val, reg);
Re-running the elf file with the above change will result in the
register setting 0x3 instead of the intended 0x1. There are other
hardware blocks which may not behave very well with a re-initialization
without proper shutdown.
To help narrow the debug down, it is usually simpler to use the
standard boot media to get to the bootloader and debug only in the area
of interest.
In general, to debug u-boot spl/u-boot with OpenOCD there are three steps:
* Modify the code adding a loop to allow the debugger to attach
near the point of interest. Boot up normally to stop at the loop.
* Connect with OpenOCD and step out of the loop.
* Step through the code to find the root of issue.
Typical debugging involves a few iterations of the above sequence.
Though most bootloader developers like to use printf to debug,
debug with JTAG tends to be most efficient since it is possible to
investigate the code flow and inspect hardware registers without
repeated iterations.
Code modification
"""""""""""""""""
* **start.S**: Adding an infinite while loop at the very entry of
U-Boot. For this, look for the corresponding start.S entry file.
This is usually only required when debugging some core SoC or
processor related function. For example: arch/arm/cpu/armv8/start.S or
arch/arm/cpu/armv7/start.S
.. code-block:: diff
diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
index 69e281b086..744929e825 100644
--- a/arch/arm/cpu/armv7/start.S
+++ b/arch/arm/cpu/armv7/start.S
@@ -37,6 +37,8 @@
#endif
reset:
+dead_loop:
+ b dead_loop
/* Allow the board to save important registers */
b save_boot_params
save_boot_params_ret:
* **board_init_f**: Adding an infinite while loop at the board entry
function. In many cases, it is important to debug the boot process if
any changes are made for board-specific applications. Below is a step
by step process for debugging the boot SPL or Armv8 SPL:
To debug the boot process in either domain, we will first
add a modification to the code we would like to debug.
In this example, we will debug ``board_init_f`` inside
``arch/arm/mach-k3/{soc}_init.c``. Since some sections of U-Boot
will be executed multiple times during the bootup process of K3
devices, we will need to include either ``CONFIG_CPU_ARM64`` or
``CONFIG_CPU_V7R`` to catch the CPU at the desired place during the
bootup process (Main or Wakeup domains). For example, modify the
file as follows (depending on need):
.. code-block:: c
void board_init_f(ulong dummy)
{
.
.
/* Code to run on the R5F (Wakeup/Boot Domain) */
if (IS_ENABLED(CONFIG_CPU_V7R)) {
volatile int x = 1;
while(x) {};
}
...
/* Code to run on the ARMV8 (Main Domain) */
if (IS_ENABLED(CONFIG_CPU_ARM64)) {
volatile int x = 1;
while(x) {};
}
.
.
}
Connecting with OpenOCD for a debug session
"""""""""""""""""""""""""""""""""""""""""""
Startup OpenOCD to debug the platform as follows:
* **Integrated JTAG interface**: If the evm has a debugger such as
XDS110 inbuilt, there is typically an evm board support added and a
cfg file will be available.
.. k3_rst_include_start_openocd_cfg_XDS110
.. code-block:: bash
openocd -f board/{board_of_choice}.cfg
.. k3_rst_include_end_openocd_cfg_XDS110
.. k3_rst_include_start_openocd_cfg_external_intro
* **External JTAG adapter/interface**: In other cases, where an
adapter/dongle is used, a simple cfg file can be created to integrate the
SoC and adapter information. See `supported TI K3 SoCs
<https://github.com/openocd-org/openocd/blob/master/tcl/target/ti_k3.cfg#L59>`_
to decide if the SoC is supported or not.
.. code-block:: bash
openocd -f openocd_connect.cfg
.. k3_rst_include_end_openocd_cfg_external_intro
For example, with BeaglePlay (AM62X platform), the openocd_connect.cfg:
.. code-block:: tcl
# TUMPA example:
# http://www.tiaowiki.com/w/TIAO_USB_Multi_Protocol_Adapter_User's_Manual
source [find interface/ftdi/tumpa.cfg]
transport select jtag
# default JTAG configuration has only SRST and no TRST
reset_config srst_only srst_push_pull
# delay after SRST goes inactive
adapter srst delay 20
if { ![info exists SOC] } {
# Set the SoC of interest
set SOC am625
}
source [find target/ti_k3.cfg]
ftdi tdo_sample_edge falling
# Speeds for FT2232H are in multiples of 2, and 32MHz is tops
# max speed we seem to achieve is ~20MHz.. so we pick 16MHz
adapter speed 16000
Below is an example of the output of this command:
.. code-block:: console
Info : Listening on port 6666 for tcl connections
Info : Listening on port 4444 for telnet connections
Info : XDS110: connected
Info : XDS110: vid/pid = 0451/bef3
Info : XDS110: firmware version = 3.0.0.20
Info : XDS110: hardware version = 0x002f
Info : XDS110: connected to target via JTAG
Info : XDS110: TCK set to 2500 kHz
Info : clock speed 2500 kHz
Info : JTAG tap: am625.cpu tap/device found: 0x0bb7e02f (mfg: 0x017 (Texas Instruments), part: 0xbb7e, ver: 0x0)
Info : starting gdb server for am625.cpu.sysctrl on 3333
Info : Listening on port 3333 for gdb connections
Info : starting gdb server for am625.cpu.a53.0 on 3334
Info : Listening on port 3334 for gdb connections
Info : starting gdb server for am625.cpu.a53.1 on 3335
Info : Listening on port 3335 for gdb connections
Info : starting gdb server for am625.cpu.a53.2 on 3336
Info : Listening on port 3336 for gdb connections
Info : starting gdb server for am625.cpu.a53.3 on 3337
Info : Listening on port 3337 for gdb connections
Info : starting gdb server for am625.cpu.main0_r5.0 on 3338
Info : Listening on port 3338 for gdb connections
Info : starting gdb server for am625.cpu.gp_mcu on 3339
Info : Listening on port 3339 for gdb connections
.. note::
Notice the default configuration is non-SMP configuration allowing
for each of the core to be attached and debugged simultaneously.
ARMv8 SPL/U-Boot starts up on cpu0 of a53/a72.
.. k3_rst_include_start_openocd_cfg_external_gdb
To debug using this server, use GDB directly or your preferred
GDB-based IDE. To start up GDB in the terminal, run the following
command.
.. code-block:: bash
gdb-multiarch
To connect to your desired core, run the following command within GDB:
.. code-block:: bash
target extended-remote localhost:{port for desired core}
To load symbols:
.. warning::
SPL and U-Boot does a re-location of address compared to where it
is loaded originally. This step takes place after the DDR size is
determined from dt parsing. So, debugging can be split into either
"before re-location" or "after re-location". Please refer to the
file ''doc/README.arm-relocation'' to see how to grab the relocation
address.
* Prior to relocation:
.. code-block:: bash
symbol-file {path to elf file}
* After relocation:
.. code-block:: bash
# Drop old symbol file
symbol-file
# Pick up new relocaddr
add-symbol-file {path to elf file} {relocaddr}
.. k3_rst_include_end_openocd_cfg_external_gdb
In the above example of AM625,
.. code-block:: bash
target extended-remote localhost:3338 <- R5F (Wakeup Domain)
target extended-remote localhost:3334 <- A53 (Main Domain)
The core can now be debugged directly within GDB using GDB commands or
if using IDE, as appropriate to the IDE.
Stepping through the code
"""""""""""""""""""""""""
`GDB TUI Commands
<https://sourceware.org/gdb/onlinedocs/gdb/TUI-Commands.html>`_ can
help set up the display more sensible for debug. Provide the name
of the layout that can be used to debug. For example, use the GDB
command ``layout src`` after loading the symbols to see the code and
breakpoints. To exit the debug loop added above, add any breakpoints
needed and run the following GDB commands to step out of the debug
loop set in the ``board_init_f`` function.
.. code-block:: bash
set x = 0
continue
The platform has now been successfully setup to debug with OpenOCD
using GDB commands or a GDB-based IDE. See `OpenOCD documentation for
GDB <https://openocd.org/doc/html/GDB-and-OpenOCD.html>`_ for further
information.
.. warning::
On the K3 family of devices, a watchdog timer within the DMSC is
enabled by default by the ROM bootcode with a timeout of 3 minutes.
The watchdog timer is serviced by System Firmware (SYSFW) or TI
Foundational Security (TIFS) during normal operation. If debugging
the SPL before the SYSFW is loaded, the watchdog timer will not get
serviced automatically and the debug session will reset after 3
minutes. It is recommended to start debugging SPL code only after
the startup of SYSFW to avoid running into the watchdog timer reset.
Miscellaneous notes with OpenOCD
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Currently, OpenOCD does not support tracing for K3 platforms. Tracing
function could be beneficial if the bug in code occurs deep within
nested function and can optionally save developers major trouble of
stepping through a large quantity of code.