Before following this guide, make sure you've followed the [dependency installation and software build instructions]({{< relref “getting_started” >}}).
Do you want to try out OpenTitan, but don't have a couple thousand or million dollars ready for an ASIC tapeout? Running OpenTitan on an FPGA board can be the answer!
To use the OpenTitan on an FPGA you need two things:
Depending on the design/target combination that you want to synthesize you will need different tools and boards. Refer to the design documentation for information on what exactly is needed.
To run OpenTitan on an FPGA, you will need an FPGA bitstream. You can either download the latest bitstream for the ChipWhisperer CW310 board or build it yourself.
If you are using the ChipWhisperer CW310 board with the Xilinx Kintex 7 XC7K410T FPGA, you can download the latest passing pre-built bitstream.
For example, to download and unpack the bitstream, run the following:
mkdir -p /tmp/bitstream-latest cd /tmp/bitstream-latest curl https://storage.googleapis.com/opentitan-bitstreams/master/bitstream-latest.tar.gz -o bitstream-latest.tar.gz tar -xvf bitstream-latest.tar.gz
By default, the bitstream is built with a version of the boot ROM used for testing (called the test ROM; pulled from sw/device/lib/testing/test_rom). There is also a version of the boot ROM used in production (called the ROM; pulled from sw/device/silicon_creator/rom). When the bitstream cache is used in bazel flows, the ROMs from the cache are not used. Instead, the bazel-built ROMs are spliced into the image to create new bitstreams, using the mechanism described in the [FPGA Reference Manual]({{< relref “ref_manual_fpga.md#boot-rom-development” >}}). The metadata for the latest bitstream (the approximate creation time and the associated commit hash) is also available as a text file and can be downloaded separately.
@bitstreams repositoryOpenTitan's build system automatically fetches pre-built bitstreams via the @bitstreams repository.
To keep the @bitstreams repository in sync with the current Git revision, install the Git post-checkout hook:
cp util/git/hooks/post-checkout .git/hooks/
Synthesizing a design for an FPGA board is simple with Bazel. While Bazel is the entry point for kicking off the FPGA synthesis, under the hood, it invokes FuseSoC, the hardware package manager / build system supported by OpenTitan. During the build process, the boot ROM is baked into the bitstream. As mentioned above, we maintain two boot ROM programs, one for testing (test ROM), and one for production (ROM).
To build an FPGA bitstream with the test ROM, use:
cd $REPO_TOP bazel build //hw/bitstream/vivado:fpga_cw310_test_rom
To build an FPGA bitstream with the ROM, use:
cd $REPO_TOP bazel build //hw/bitstream/vivado:fpga_cw310_rom
Note, building these bitstreams will require Vivado be installed on your system, with access to the proper licenses, described [here]({{< relref “doc/getting_started/install_vivado” >}}). For general software development on the FPGA, Vivado must still be installed, but the Lab Edition is sufficient.
The default Vivado tool placement may sometimes result in congested FPGA floorplans. When this happens, the implementation time and results become unpredictable. It may become necessary for the user to manually adjust certain placement. See this comment for a thorough analysis of one such situation and what changes were made to improve congestion.
Sometimes, it may be desirable to open the generated project in the Vivado GUI for inspection. To this end, run:
. /tools/Xilinx/Vivado/{{< tool_version "vivado" >}}/settings64.sh cd $REPO_TOP make -C $(dirname $(find bazel-out/* -wholename '*synth-vivado/Makefile')) build-gui
Now the Vivado GUI opens and loads the project.
TODO(lowRISC/opentitan#13213): the below does not work with the Bazel FPGA bitstream build flow.
Sometimes it is helpful to use the Vivado GUI to debug a design. FuseSoC (the tool Bazel invokes) makes that easy, with one small caveat: by default FuseSoC copies all source files into a staging directory before the synthesis process starts. This behavior is helpful to create reproducible builds and avoids Vivado modifying checked-in source files. But during debugging this behavior is not helpful. The --no-export option of FuseSoC disables copying the source files into the staging area, and --setup instructs fusesoc to not start the synthesis process.
# Only create Vivado project directory by using FuseSoC directly (skipping Bazel invocation). cd $REPO_TOP fusesoc --cores-root . run --flag=fileset_top --target=synth --no-export --setup lowrisc:systems:chip_earlgrey_cw310
You can then navigate to the created project directory, and open Vivado
. /tools/Xilinx/Vivado/{{< tool_version "vivado" >}}/settings64.sh cd $REPO_TOP/build/lowrisc_systems_chip_earlgrey_cw310_0.1/synth-vivado/ vivado
Finally, using the Tcl console, you can kick off the project setup with
source lowrisc_systems_chip_earlgrey_cw310_0.1.tcl
The ChipWhisperer CW310 board supports different power options. It is recommended to power the board via the included DC power adapter. To this end:
You can now use the following to monitor output from dmesg:
sudo dmesg -Hw
This should show which serial ports have been assigned, or if the board is having trouble connecting to USB. If dmesg reports a problem you can trigger a USB_RST with SW5. When properly connected, dmesg should identify the board, not show any errors, and the status light should flash. They should be named '/dev/ttyACM*', e.g. /dev/ttyACM1. To ensure that you have sufficient access permissions, set up the udev rules as explained in the [Vivado installation instructions]({{< relref “install_vivado” >}}).
You will then need to run this command to configure the board. You only need to run it once.
bazel run //sw/host/opentitantool -- --interface=cw310 fpga set-pll
Check that it's working by [running the demo]({{< relref “#hello-world-demo” >}}) or a test, such as the uart_smoketest below.
cd $REPO_TOP bazel test --test_output=streamed //sw/device/tests:uart_smoketest_fpga_cw310_test_rom
If the tests/demo aren't working on the FPGA (especially if you get an error like SFDP header contains incorrect signature) then try adding --rcfile= to the set-pll command:
bazel run //sw/host/opentitantool -- --rcfile= --interface=cw310 fpga set-pll
It's also worth pressing the USB_RST and USR_RESET buttons on the FPGA if you face continued errors.
There are two ways to load a bitstream on to the FPGA and bootstrap software into the OpenTitan embedded flash:
bazel test ....opentitantool, and Which one you use, will depend on how the build target is defined for the software you would like to test on the FPGA. Specifically, for software build targets defined in Bazel BUILD files using the opentitan_functest Bazel macro, you will use the latter (automatic) approach. Alternatively, for software build targets defined in Bazel BUILD files using the opentitan_flash_binary Bazel macro, you will use the former (manual) approach.See below for details on both approaches.
A majority of on-device software tests are defined using the custom opentitan_functest Bazel macro, which under the hood, instantiates several Bazel native.sh_test rules. In doing so, this macro provides a convenient interface for developers to run software tests on OpenTitan FPGA instances with a single invocation of bazel test .... For example, to run the UART smoke test (which is an opentitan_functest defined in sw/device/tests/BUILD) on FPGA hardware, and see the output in real time, use:
cd $REPO_TOP bazel test --test_tag_filters=cw310 --test_output=streamed //sw/device/tests:uart_smoketest
or
cd $REPO_TOP bazel test --test_output=streamed //sw/device/tests:uart_smoketest_fpga_cw310_test_rom
Under the hood, Bazel conveniently dispatches opentitantool to both:
To get a better understanding of the opentitantool functions Bazel invokes automatically, follow the instructions for manually loading FPGA bitstreams below.
By default, the above invocations of bazel test ... use the pre-built (Internet downloaded) FPGA bitstream. To instruct bazel to load the bitstream built earlier, or to have bazel build an FPGA bitstream on the fly, and load that bitstream onto the FPGA, add the --define bitstream=vivado flag to either of the above Bazel commands, for example, run:
bazel test --define bitstream=vivado --test_output=streamed //sw/device/tests:uart_smoketest_fpga_cw310_test_rom
Alternatively, if you would like to instruct Bazel to skip loading any bitstream at all, and simply use the bitstream that is already loaded, add the --define bitstream=skip flag, for example, run:
bazel test --define bitstream=skip --test_output=streamed //sw/device/tests:uart_smoketest_fpga_cw310_test_rom
opentitantoolSome on-device software targets are defined using the custom opentitan_flash_binary Bazel macro. Unlike the opentitan_functest macro, the opentitan_flash_binary macro does not instantiate any Bazel test rules under the hood. Therefore, to run such software on OpenTitan FPGA hardware, both a bitstream and the software target must be loaded manually onto the FPGA. Below, we describe how to accomplish this, and in doing so, we shed some light on the tasks that Bazel automates through the use of opentitan_functest Bazel rules.
opentitantoolNote: The following examples assume that you have a ~/.config/opentitantool/config with the proper --interface option. For the CW310, its contents would look like:
--interface=cw310
To flash the bitstream onto the FPGA using opentitantool, use the following command:
cd $REPO_TOP ### If you downloaded the bitstream from the Internet: bazel run //sw/host/opentitantool fpga load-bitstream /tmp/bitstream-latest/lowrisc_systems_chip_earlgrey_cw310_0.1.bit.orig ### If you built the bitstream yourself: bazel run //sw/host/opentitantool fpga load-bitstream $(ci/scripts/target-location.sh //hw/bitstream/vivado:fpga_cw310_test_rom)
Depending on the FPGA device, the flashing itself may take several seconds. After completion, a message like this should be visible from the UART:
I00000 test_rom.c:81] Version: earlgrey_silver_release_v5-5886-gde4cb1bb9, Build Date: 2022-06-13 09:17:56 I00001 test_rom.c:87] TestROM:6b2ca9a1 I00002 test_rom.c:118] Test ROM complete, jumping to flash!
The hello_world demo software shows off some capabilities of the OpenTitan hardware. To load hello_world into the FPGA on the ChipWhisperer CW310 board follow the steps shown below.
Generate the bitstream and flash it to the FPGA as described above.
Open a serial console (use the device file determined before) and connect. Settings: 115200 baud, 8 bits per byte, no software flow-control for sending and receiving data.
screen /dev/ttyACM1 115200,cs8,-ixon,-ixoff
Run opentitantool.
cd ${REPO_TOP} bazel run //sw/host/opentitantool -- --interface=cw310 fpga set-pll # This needs to be done only once. bazel build //sw/device/examples/hello_world:hello_world_fpga_cw310_bin bazel run //sw/host/opentitantool bootstrap $(ci/scripts/target-location.sh //sw/device/examples/hello_world:hello_world_fpga_cw310_bin)
and then output like this should appear from the UART:
I00000 test_rom.c:81] Version: earlgrey_silver_release_v5-5886-gde4cb1bb9, Build Date: 2022-06-13 09:17:56 I00001 test_rom.c:87] TestROM:6b2ca9a1 I00000 test_rom.c:81] Version: earlgrey_silver_release_v5-5886-gde4cb1bb9, Build Date: 2022-06-13 09:17:56 I00001 test_rom.c:87] TestROM:6b2ca9a1 I00002 test_rom.c:118] Test ROM complete, jumping to flash! I00000 hello_world.c:66] Hello World! I00001 hello_world.c:67] Built at: Jun 13 2022, 14:16:59 I00002 demos.c:18] Watch the LEDs! I00003 hello_world.c:74] Try out the switches on the board I00004 hello_world.c:75] or type anything into the console window. I00005 hello_world.c:76] The LEDs show the ASCII code of the last character.
Observe the output both on the board and the serial console. Type any text into the console window.
Exit screen by pressing CTRL-a k, and confirm with y.
If the firmware load fails, try pressing the “USR-RST” button before loading the bitstream.
The CW310 supports JTAG-based debugging with OpenOCD and GDB via the standard ARM JTAG headers on the board (labeled USR Debug Headers). To use it, program the bitstream and bootstrap the desired firmware, then connect a JTAG adapter to one of the headers. For this guide, the Olimex ARM-USB-TINY-H JTAG adapter was used.
After bootstrapping the firmware, the TAP straps may need to be set. As of this writing, the FPGA images are typically programmed to be in the RMA lifecycle state, and the TAP straps are sampled continuously in that state. To connect the JTAG chain to the CPU's TAP, adjust the strap values with opentitantool. Assuming opentitantool has been built and that the current directory is the root of the workspace, run these commands:
./bazel-bin/sw/host/opentitantool/opentitantool \ --interface cw310 \ gpio write TAP_STRAP0 false ./bazel-bin/sw/host/opentitantool/opentitantool \ --interface cw310 \ gpio write TAP_STRAP1 true
Connect a JTAG adapter to one of the headers. For the Olimex ARM-USB-TINY-H, use the classic ARM JTAG header (J13) and make sure switch S2 is set to 3.3 V. Depending on the adapter's default state, OpenTitan may be held in reset when the adapter is initially connected. This reset will come under software control once OpenOCD initializes the driver.
The JTAG adapter‘s device node in /dev must have read-write permissions. Otherwise, OpenOCD will fail because it’s unable to open the USB device. The udev rule below matches the ARM-USB-TINY-H adapter, sets the octal mode mask to 0666, and creates a symlink at /dev/jtag_adapter_arm_usb_tiny_h.
# [/etc/udev/rules.d/90-jtag-adapter.rules]
SUBSYSTEM=="usb", ATTRS{idVendor}=="15ba", ATTRS{idProduct}=="002a", MODE="0666", SYMLINK+="jtag_adapter_arm_usb_tiny_h"
Now, reload the udev rules and reconnect the JTAG adapter.
# Reload the udev rules. sudo udevadm control --reload-rules sudo udevadm trigger # Physically disconnect and reconnect the JTAG adapter, or fake it: sudo udevadm trigger --verbose --type=subsystems --action=remove --subsystem-match=usb --attr-match="idVendor=15ba" sudo udevadm trigger --verbose --type=subsystems --action=add --subsystem-match=usb --attr-match="idVendor=15ba" # Print the permissions of the USB device. This command should print "666". stat --dereference -c '%a' /dev/jtag_adapter_arm_usb_tiny_h
To connect the ChipWhisperer CW310 FPGA board with OpenOCD, run the following command:
cd $REPO_TOP openocd -f <adapter-config.cfg> \ -c "adapter speed 500; transport select jtag; reset_config trst_and_srst" \ -f util/openocd/target/lowrisc-earlgrey.cfg
For the Olimex ARM-USB-TINY-H with a Debian-based distro, the adapter configuration would be at /usr/share/openocd/scripts/interface/ftdi/olimex-arm-usb-tiny-h.cfg. So for that particular case, the command would be the following:
cd $REPO_TOP openocd -f /usr/share/openocd/scripts/interface/ftdi/olimex-arm-usb-tiny-h.cfg \ -c "adapter speed 500; transport select jtag; reset_config trst_and_srst" \ -f util/openocd/target/lowrisc-earlgrey.cfg
Example OpenOCD output:
Open On-Chip Debugger 0.11.0 Licensed under GNU GPL v2 For bug reports, read http://openocd.org/doc/doxygen/bugs.html trst_and_srst separate srst_gates_jtag trst_push_pull srst_open_drain connect_deassert_srst Info : Hardware thread awareness created force hard breakpoints Info : Listening on port 6666 for tcl connections Info : Listening on port 4444 for telnet connections Info : clock speed 1000 kHz Info : JTAG tap: riscv.tap tap/device found: 0x04f5484d (mfg: 0x426 (Google Inc), part: 0x4f54, ver: 0x0) Info : datacount=2 progbufsize=8 Info : Examined RISC-V core; found 1 harts Info : hart 0: XLEN=32, misa=0x40101106 Info : starting gdb server for riscv.tap.0 on 3333 Info : Listening on port 3333 for gdb connections
Note that the reset_config command may need to be adjusted for the particular JTAG adapter in use. TRSTn is available on the 20-pin ARM JTAG header only. Use srst_only if the adapter only supports SRSTn.
See the [install instructions]({{< relref “install_openocd” >}}) for guidance on installing OpenOCD.
To actually debug through OpenOCD, it must either be connected through telnet or GDB.
The following is an example for using telnet
telnet localhost 4444 // or whatever port that is specificed by the openocd command above mdw 0x8000 0x10 // read 16 bytes at address 0x8000
First, make sure the device software has been built with debug symbols (by default Bazel does not build software with debug symbols). For example, to build and test the UART smoke test with debug symbols, you can add --copt=-g flag to the bazel test ... command:
cd $REPO_TOP bazel test --copt=-g --test_output=streamed //sw/device/tests:uart_smoketest_fpga_cw310_test_rom
Then a connection between OpenOCD and GDB may be established with:
cd $REPO_TOP ./bazelisk.sh build --config=riscv32 //sw/device/tests:uart_smoketest_prog_fpga_cw310.elf riscv32-unknown-elf-gdb -ex "target extended-remote :3333" -ex "info reg" \ "$(./bazelisk.sh outquery --config=riscv32 //sw/device/tests:uart_smoketest_prog_fpga_cw310.elf)"
The above will print out the contents of the registers upon successs. Note that you should have the RISC-V toolchain installed and on your PATH. For example, if you followed the [Getting Started]({{< relref “getting_started#step-3-install-the-lowrisc-risc-v-toolchain” >}}) instructions, then make sure /tools/riscv/bin is on your PATH.
Examine 16 memory words in the hex format starting at 0x200005c0
(gdb) x/16xw 0x200005c0
Press enter again to print the next 16 words. Use help x to get a description of the command.
If the memory content contains program text it can be disassembled
(gdb) disassemble 0x200005c0,0x200005c0+16*4
Displaying the memory content can also be delegated to OpenOCD
(gdb) monitor mdw 0x200005c0 16
Use monitor help to get a list of supported commands.
To single-step use stepi or step
(gdb) stepi
stepi single-steps an instruction, step single-steps a line of source code. When testing debugging against the hello_world binary it is likely you will break into a delay loop. Here the step command will seem to hang as it will attempt to step over the whole delay loop with a sequence of single-step instructions which may take quite some time!
To change the program which is debugged the file command can be used. This will update the symbols which are used to get information about the program. It is especially useful in the context of our rom.elf, which resides in the ROM region, which will eventually jump to a different executable as part of the flash region.
(gdb) file sw/device/examples/hello_world/sw.elf (gdb) disassemble 0x200005c0,0x200005c0+16*4
The output of the disassemble should now contain additional information.
When an FPGA test fails in CI, it can be helpful to run the tests locally with the version of the bitstream generated by the failing CI run. To avoid rebuilding the bitstream, you can download the bitstream artifact from the Azure Pipeline CI run and use opentitantool to load the bitstream manually.
To download the bitstream:
Note that Azure does not allow you to download the artifact with wget or curl by default, so to use the download URL, you need to specify a user-agent header. For example, to download with curl, you can use the following command
curl --output /tmp/artifact.tar.gz -H 'user-agent: Mozilla/5.0' <download_URL>
After extracting the artifact, the bitstream is located at build-bin/hw/top_earlgrey/lowrisc_systems_chip_earlgrey_cw310_0.1.bit.{splice,orig}. The .splice bitstream has the ROM spliced in, and the .orig bitstream has the test ROM.
Next, load the bitstream with opentitantool, and run the test. The FPGA tests attempt to load the latest bitstream by default, but because we wish to use the bitstream that we just loaded, we need to tell Bazel to skip the automatic bitstream loading.
# Load the bitstream with opentitantool bazel run //sw/host/opentitantool --interface=cw310 fpga load-bitstream <path_to_your_bitstream> # Run the broken test locally, showing all test output and skipping the bitstream loading bazel test <broken_test_rule> --define bitstream=skip --test_output=streamed