Examples and exercises for the DecaWave DWM1001-DEV devkits utilized at the RTFM Workshop held at Oxidize 2019, Berlin.

For installation of all required software to run the DWM1001-DEV board, follow the instruction here: Installation instruction, and the verify with the Verification instructions.

The DWM1001-DEV uses a JLink debugger onboard.

1. Connect your devkit using USB. To check that it is found you can run:

$ lsusb
...
Bus 001 Device 005: ID 1366:0105 SEGGER
...

(Bus/Device/ID may vary.)

2. In a terminal in the app folder run:

$ JLinkGDBServer -device NRF52832_XXAA -if SWD -speed 4000
...
Connecting to J-Link...
J-Link is connected.
Firmware: J-Link OB-STM32F072-128KB-CortexM compiled Jan  7 2019 14:08:04
Hardware: V1.00
S/N: 760040473
Checking target voltage...
Target voltage: 3.30 V
Listening on TCP/IP port 2331
Connecting to target...Connected to target
Waiting for GDB connection...
...

3. In another terminal (in the same app folder) run:

$ cargo run --example minimal

This starts GDB with a connection to JLink, which loads (flashes) the binary to the target (our devkit). The script sets breakpoints at main as well as some exception handlers, enables semihosting, loads the binary and finally runs the first instruction (stepi). Exactly what is run can be found in the jlink.gdb file.

4. You can now continue debugging of the program:

(gdb) c
Continuing.

Breakpoint 3, main () at examples/minimal.rs:18
18          hprintln!("hello").unwrap();

The cortex-m-rt run-time initializes the system and your global variables (in this case there are none). After that it calls the [entry] function. Here you hit a breakpoint.

5. You can continue debugging:

(gdb) c
Continuing.

At this point, the GDB terminal should read:

hello

Your program is now stuck in an infinite loop (doing nothing).

6. Press CTRL-c in the gdb terminal:

Program received signal SIGINT, Interrupt.
0x08000276 in main () at examples/minimal.rs:20
20          loop {}
(gdb)

1. Connect your devkit using USB. To check that it is found you can run:

$ lsusb
...
Bus 001 Device 005: ID 1366:0105 SEGGER
...

(Bus/Device/ID may vary.)

2. In a terminal in the app folder run:

$ cargo build --example minimal
$ openocd -f openocd_jlink.cfg
...
Info : J-Link OB-STM32F072-128KB-CortexM compiled Jan  7 2019 14:08:04
Info : Hardware version: 1.00
Info : VTarget = 3.300 V
...

3. In another terminal (in the same app folder) run:

$ arm-none-eabi-gdb target/thumbv7em-none-eabihf/debug/examples/minimal -x jlink.gdb

This starts GDB with a connection to the JLink via OpenOCD, which loads (flashes) the binary to the target (our devkit). The script sets breakpoints at main as well as some exception handlers, enables semihosting, loads the binary and finally runs the first instruction (stepi). Exactly what is run can be found in the jlink.gdb file.

4. You can now continue debugging of the program:

(gdb) c
Continuing.

Breakpoint 3, main () at examples/minimal.rs:18
18          hprintln!("hello").unwrap();

The cortex-m-rt run-time initializes the system and your global variables (in this case there are none). After that it calls the [entry] function. Here you hit a breakpoint.

5. You can continue debugging:

(gdb) c
Continuing.

At this point, the GDB terminal should read:

hello

Your program is now stuck in an infinite loop (doing nothing).

6. Press CTRL-c in the gdb terminal:

Program received signal SIGINT, Interrupt.
0x08000276 in main () at examples/minimal.rs:20
20          loop {}
(gdb)

You have now compiled and debugged a minimal Rust example! gdb is a very useful tool so lookup some tutorials/docs (e.g., https://sourceware.org/gdb/onlinedocs/gdb/), a Cheat Sheet can be found at https://darkdust.net/files/GDB%20Cheat%20Sheet.pdf.

Working with embedded targets involves a lot of tooling, and many things can go wrong.

If you end up with a program that puts the MCU in a bad state.

• Check so the board in connected.
• Ask an instructor.

JLink acts as a gdb server, while gdb is a gdb client. By default they connect over port :2331 (: indicates that the port is on the localhost, not a remote connection). In cases you might have another gdb connection blocking the port.

$ ps -all
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S  1000  7549 16215  0  80   0 - 25930 se_sys pts/4    00:00:00 arm-none-eabi-gdb
...

In this case you can try killing gdb by:

$ kill -9 7549

or even

$ killall -9 arm-none-eabi-gdb

vscode is highly configurable, (keyboard shortcuts, keymaps, plugins etc.) There is Rust support through the rls-vscode plugin (https://github.com/rust-lang/rls-vscode).

It is possible to run arm-none-eabi-gdb from within the vscode using the cortex-debug plugin (https://marketplace.visualstudio.com/items?itemName=marus25.cortex-debug).

For general informaiton regarding debugging in vscode, see https://code.visualstudio.com/docs/editor/debugging.

Some useful (default) shortcuts:

• CTRL+SHIFT+b compilation tasks, (e.g., compile all examples cargo build --examples). Cargo is smart and just re-compiles what is changed.

• CTRL+SHIFT+d debug launch configurations, enter debug mode to choose a binary (e.g., itm 64MHz (debug))

• F5 to start. It will open the cortex_m_rt/src/lib.rs file, which contains the startup code. From there you can continue F5 again.

• F6 to break. The program will now be in the infinite loop (for this example). In general it will just break wherever the program counter happens to be.

• You can view the ITM trace in the OUTPUT tab, choose the dropdown SWO: ITM [port 0, type console]. It should now display:

[2019-01-02T21:35:26.457Z]   Hello, world!

• SHIFT-F5 shuts down the debugger.

You may step, view the current context variables, add watches, inspect the call stack, add breakpoints, inspect peripherals and registers. Read more in the documentation for the plugin.

Visual Studio Code is not an "IDE", its a text editor with plugin support, with an API somewhat limiting what can be done from within a plugin (in comparison to Eclipse, IntelliJ...) regarding panel layouts etc. E.g., as far as I know you cannot view the adapter output (openocd) at the same time as the ITM trace, they are both under the OUTPUT tab. Moreover, each time you re-start a debug session, you need to re-select the SWO: Name [port 0, type console] to view the ITM output. There are some hax around this:

• Never shut down the debug session. Instead use the DEBUG CONSOLE (CTRL+SHIFT+Y) to get to the gdb console. This is not the full gdb interactive shell with some limitations (no tab completion e.g.). Make sure the MCU is stopped (F6). The console should show something like:

Program
 received signal SIGINT, Interrupt.
0x0800056a in main () at examples/itm.rs:31
31	    loop {}

• Now you can edit an re-compile your program, e.g. changing the text:

iprintln!(stim, "Hello, again!");

• In the DEBUG CONSOLE, write load press ENTER write monitor reset init press ENTER.

load
{"token":97,"outOfBandRecord":[{"isStream":false,"type":"status","asyncClass":"download","output":[]}]}
`/home/pln/rust/app/target/thumbv7em-none-eabihf/debug/examples/itm' has changed; re-reading symbols.
Loading section .vector_table, size 0x400 lma 0x8000000
Loading section .text, size 0x10c8 lma 0x8000400
Loading section .rodata, size 0x2a8 lma 0x80014d0
Start address 0x8001298, load size 6000
Transfer rate: 9 KB/sec, 2000 bytes/write.

mon reset init
{"token":147,"outOfBandRecord":[],"resultRecords":{"resultClass":"done","results":[]}}
adapter speed: 2000 kHz
target halted due to debug-request, current mode: Thread
xPSR: 0x01000000 pc: 0x08001298 msp: 0x20018000
adapter speed: 8000 kHz

• The newly compiled binary is now loaded and you can continue (F5). Switching to the OUTPUT window now preserves the ITM view and displays both traces:

[2019-01-02T21:43:27.988Z]   Hello, world!
[2019-01-02T22:07:29.090Z]   Hello, again!

• Using the gdb terminal (DEBUG CONSOLE) from within vscode is somewhat instable/experimental. E.g., CTRL+c does not break the target (use F6, or write interrupt). The contiune command, indeed continues execution (and the control bar changes mode, but you cannot break using neither F6 nor interrupt). So it seems that the state of the cortex-debug plugin is not correctly updated. Moreover setting breakpoints from the gdb terminal indeed informs gdb about the breakpoint, but the state in vscode is not updated, so be aware.

Some example launch configurations from the .vscode/launch.json file:

 {
            "type": "cortex-debug",
            "request": "launch",
            "servertype": "openocd",
            "name": "itm 64Mhz (debug)",
            "executable": "./target/thumbv7em-none-eabihf/debug/examples/itm",
            "configFiles": [
                "interface/stlink.cfg",
                "target/stm32f4x.cfg"
            ],
            "postLaunchCommands": [
                "monitor reset init"
            ],
            "swoConfig": {
                "enabled": true,
                "cpuFrequency": 64000000,
                "swoFrequency": 2000000,
                "source": "probe",
                "decoders": [
                    {
                        "type": "console",
                        "label": "ITM",
                        "port": 0
                    }
                ]
            },
            "cwd": "${workspaceRoot}"
        },
        {
            "type": "cortex-debug",
            "request": "launch",
            "servertype": "openocd",
            "name": "hello 16Mhz (debug)",
            "executable": "./target/thumbv7em-none-eabihf/debug/examples/hello",
            "configFiles": [
                "interface/stlink.cfg",
                "target/stm32f4x.cfg"
            ],
            "postLaunchCommands": [
                "monitor arm semihosting enable"
            ],
            "cwd": "${workspaceRoot}"
        },

      {
            "type": "cortex-debug",
            "request": "launch",
            "servertype": "openocd",
            "name": "itm 16Mhz (debug)",
            "executable": "./target/thumbv7em-none-eabihf/debug/examples/itm",
            // uses local config files
            "configFiles": [
                "./stlink.cfg",
                "./stm32f4x.cfg"
            ],
            "postLaunchCommands": [
                "monitor reset init"
            ],
            "swoConfig": {
                "enabled": true,
                "cpuFrequency": 16000000,
                "swoFrequency": 2000000,
                "source": "probe",
                "decoders": [
                    {
                        "type": "console",
                        "label": "ITM",
                        "port": 0
                    }
                ]
            },
            "cwd": "${workspaceRoot}"
        },

We see some similarities to the openocd.gdb file, we don't need to explicitly connect to the target (that is automatic). Also launching openocd is automatic (for good and bad, its re-started each time). postLaunchCommands allows arbitrary commands to be executed by gdb once the session is up. E.g. in the hello case we enable semihosting, while in the itm case we run monitor reset init to get the MCU in 64MHz (first example) or 16MHz (third example), before running the application (continue). Notice the first example uses the "stock" openocd configuration files, while the third example uses our local configuration files (that does not change the core frequency).

There are numerous ways to automate gdb. Scripts can be run by the gdb command source (so for short). Scripting common tasks like setting breakpoints, dumping some memory region etc. can be really helpful.