Attempting to assign value to undefined symbol error

[mmarks]

This question may be better suited for the Zephyr forum, but I figured I would ask it here as well in case somebody can easily see what I may be missing.

I am trying to work through the solved examples in the Bluetooth Mesh Developer Study Guide found here: Bluetooth Mesh Developer Study Guide v2.0 | Bluetooth Technology Website
The code examples use Zephyr as a foundation for Bluetooth Mesh introductory examples. The Study Guide includes both starting point and solution code, and my focus is on getting the solution code examples for Switch and Light to compile.  For switch, I see this error message: "C:/Projects/BluetoothMeshDeveloperStudyGuideV2_0_0/code/solution/Switch/prj.conf:34: warning: attempt to assign the value '36' to the undefined symbol BT_MESH_RX_SDU_MAX" which appears to break the build. Complete build output here:

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C:\Projects\BluetoothMeshDeveloperStudyGuideV2_0_0\code\solution\Switch>west build -b nrf52840dk_nrf52840 --pristine

-- west build: making build dir C:\Projects\BluetoothMeshDeveloperStudyGuideV2_0_0\code\solution\Switch\build pristine

-- west build: generating a build system

-- Application: C:/Projects/BluetoothMeshDeveloperStudyGuideV2_0_0/code/solution/Switch

-- Using NCS Toolchain 1.5.0 for building. (C:/Users/mmarks/ncs/v1.5.0/toolchain/cmake)

-- Zephyr version: 2.4.99 (c:/users/mmarks/ncs/v1.5.0/zephyr)

-- Found Python3: C:/Users/mmarks/ncs/v1.5.0/toolchain/opt/bin/python.exe (found suitable exact version "3.8.2") found components: Interpreter

-- Found west (found suitable version "0.9.0", minimum required is "0.7.1")

-- Board: nrf52840dk_nrf52840

-- Cache files will be written to: C:\Users\mmarks\AppData\Local/.cache/zephyr

-- Found dtc: C:/Users/mmarks/ncs/v1.5.0/toolchain/opt/bin/dtc.exe (found suitable version "1.4.7", minimum required is "1.4.6")

-- Found toolchain: gnuarmemb (C:/Users/mmarks/ncs/v1.5.0/toolchain/opt)

-- Found BOARD.dts: C:/Users/mmarks/ncs/v1.5.0/zephyr/boards/arm/nrf52840dk_nrf52840/nrf52840dk_nrf52840.dts

-- Generated zephyr.dts: C:/Projects/BluetoothMeshDeveloperStudyGuideV2_0_0/code/solution/Switch/build/zephyr/zephyr.dts

-- Generated devicetree_unfixed.h: C:/Projects/BluetoothMeshDeveloperStudyGuideV2_0_0/code/solution/Switch/build/zephyr/include/generated/devicetree_unfixed.h

-- Generated device_extern.h: C:/Projects/BluetoothMeshDeveloperStudyGuideV2_0_0/code/solution/Switch/build/zephyr/include/generated/device_extern.h

 

C:/Projects/BluetoothMeshDeveloperStudyGuideV2_0_0/code/solution/Switch/prj.conf:34: warning: attempt to assign the value '36' to the undefined symbol BT_MESH_RX_SDU_MAX

Parsing c:/users/mmarks/ncs/v1.5.0/zephyr/Kconfig

Loaded configuration 'C:/Users/mmarks/ncs/v1.5.0/zephyr/boards/arm/nrf52840dk_nrf52840/nrf52840dk_nrf52840_defconfig'

Merged configuration 'C:/Projects/BluetoothMeshDeveloperStudyGuideV2_0_0/code/solution/Switch/prj.conf'

 

error: Aborting due to Kconfig warnings

 

CMake Error at C:/Users/mmarks/ncs/v1.5.0/zephyr/cmake/kconfig.cmake:262 (message):

  command failed with return code: 1

Call Stack (most recent call first):

  C:/Users/mmarks/ncs/v1.5.0/zephyr/cmake/app/boilerplate.cmake:534 (include)

  CMakeLists.txt:3 (include)

 

 

-- Configuring incomplete, errors occurred!

FATAL ERROR: command exited with status 1: 'C:\Program Files\CMake\bin\cmake.EXE' '-DWEST_PYTHON=c:\python39\python.exe' '-BC:\Projects\BluetoothMeshDeveloperStudyGuideV2_0_0\code\solution\Switch\build' '-SC:\Projects\BluetoothMeshDeveloperStudyGuideV2_0_0\code\solution\Switch' -GNinja -DBOARD=nrf52840dk_nrf52840
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The symbol that it complains is undefined, BT_MESH_RX_SDU_MAX, is listed in prj.conf. Is there something I'm missing why the symbol shows up as undefined?

Thanks,
Mike Marks

[hmolesworth]

Brief answer is that you can only assign a value to a variable; BT_MESH_RX_SDU_MAX may be a symbol but it is not a variable and has no storage class even though it has a value. You could say (for example)

uint32_t SomeName = BT_MESH_RX_SDU_MAX;

  SomeName = BT_MESH_RX_SDU_MAX/2;

If you want to change the value of BT_MESH_RX_SDU_MAX directly, just find the definition and change the value used in the definition.

[mmarks]

Thanks for the answer.  Maybe I'm misunderstanding because Zephyr is new to me, but the line that assigns BT_MESH_RX_SDU_MAX=36 is in the project configuration file prj.conf, which I thought is what assigns that symbol to a value similar to how #define works in C. Perhaps not?

[hmolesworth]

Yes, identical to #define but no, that value cannot be changed later unless undefined and redefined which is frowned upon and results in MISRA police action