Spin Lock Build Errors with Pico SDK on Raspberry Pi Pico 2 (RP2350)

[crcz25]

Issue Description

I'm encountering inconsistent build errors when using the Pico SDK with the new Raspberry Pi Pico 2 (RP2350). The initial build attempt fails with multiple errors related to missing spin lock implementation for the RP2350 platform. However, in a second build attempt, the process succeeds without changes, which is unexpected and confusing. What could be causing these intermittent build failures? Are there known issues with spin locks on RP2350, or what might be happening?

Error details

When building with PICO_BOARD=pico2 and PICO_PLATFORM=rp2350, I get the error below. This error occurs across multiple steps (see the output from the terminal, terminal_log.txt). This is also my building script (build.txt), and my CMakeLists (CMakeLists.txt).

#error no SW_SPIN_TRY_LOCK available for PICO_USE_SW_SPIN_LOCK on this platform

Environment

• Board: Raspberry Pi Pico 2 (RP2350)
• OS: Ubuntu 24.04 (Docker container)
• Using Pico SDK from the official repository
• Build: CMake and arm-none-eabi-gcc (version 13.2.1) using build.sh
• Platform: rp2350-arm-s
• Project: Micro-ROS implementation (currently only loading the library and example code from the Micro-ROS tutorial). The publisher/subscriber works when I'm able to compile, so no issues there.

Reproduction steps

Configure CMake with PICO_BOARD=pico2 and PICO_PLATFORM=rp2350
Run build
Build fails at compilation stage with the spin lock errors

Observations

• The first build attempt fails due to missing spin lock implementation for RP2350.
• The second attempt succeeds without any changes.
• No modifications were made between attempts, making the behavior inconsistent.

Any insights or debugging suggestions would be greatly appreciated!

[lurch]

Not directly related to your original question, but I see that https://micro.ros.org/docs/overview/hardware/ only lists RP2040 and doesn't list RP2350 yet.

[kilograham]

"first build" since what?

It sounds like you may be changing PICO_BOARD and PICO_PLATFORM based on "When building with ..."

You should delete your build directory if switching these (or just use different build directories for the different configs. Delete your build driectory (if you didn't) and see if the problem persists

This is the sort of question best asked here https://forums.raspberrypi.com/viewforum.php?f=145

[crcz25]

Thanks @lurch, for pointing out the other issue, I can now compile the code successfully!

Previously, when compiling for the RP2040, I had set CFLAGS and CXXFLAGS as follows:

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -ffunction-sections -fdata-sections")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -ffunction-sections -fdata-sections")

After commenting out these lines, the compilation worked.

To be honest, I don’t fully understand this part of CMake, and I don’t even remember why I added these flags in the first place. As far as I know, they help reduce the final binary size, am I correct?

Also, I understood that issue 452 from pico-feedback was related to the distro (ClearLinux), right? For reference, I’m compiling my code inside Docker using Ubuntu 24.04.2 LTS, while my host OS is Pop!_OS 22.04 LTS.

I'm not sure how to proceed with this issue, I think it can be closed, but not sure if any further action needs to be taken. Could these flags just be incompatible with the new Pico? 🤔