"Undefined Reference" on the linker level

[Connie Violet]

Hi. I am a beginner with nrf52832. Trying to get Bluetooth and UART and a I2C peripheral working at the same time. I had a working version of the I2C peripheral and UART working together and tried to merge Bluetooth in, referencing the ble_app_uart example provided in nRF5_SDK_12.3.0. Currently when I try to do make flash I do not get any compiling errors, but I am getting linker errors that say that I have "undefined reference":

Linking target: _build/nrf52832_xxaa.out
_build/nrf52832_xxaa_twi.c.o: In function `twi_master_init':
/home/yilunsheng/src/accelerometer, SDK12.3, app_uart_merge/./twi.c:43: undefined reference to `nrf_drv_twi_init'
/home/yilunsheng/src/accelerometer, SDK12.3, app_uart_merge/./twi.c:46: undefined reference to `nrf_drv_twi_enable'
_build/nrf52832_xxaa_lis3dh.c.o: In function `lis3dh_read_data':
/home/yilunsheng/src/accelerometer, SDK12.3, app_uart_merge/./lis3dh.c:171: undefined reference to `nrf_drv_twi_tx'
/home/yilunsheng/src/accelerometer, SDK12.3, app_uart_merge/./lis3dh.c:180: undefined reference to `nrf_drv_twi_rx'
_build/nrf52832_xxaa_lis3dh.c.o: In function `lis3dh_init':
/home/yilunsheng/src/accelerometer, SDK12.3, app_uart_merge/./lis3dh.c:232: undefined reference to `nrf_drv_twi_tx'
collect2: error: ld returned 1 exit status
../nRF5_SDK_12.3.0/components/toolchain/gcc/Makefile.common:153: recipe for target '_build/nrf52832_xxaa.out' failed
make: *** [_build/nrf52832_xxaa.out] Error 1

Very confused about where the problem is.

[awneil]

Jørgen Holmefjord said:

You have not included the source file that implements the functions in your project

This is a standard 'C' issue - nothing specifically to do with Nordic.

However, in this case, I would have thought you would have got compile errors?

Jørgen Holmefjord said:

ou have not enabled the module in your project's sdk_config.h file.

This one is specific to the way Nordic configure their SDKs.

As  Jørgen Holmefjord said, this one is a frequent cause of confusion - so maybe there's a clue for Nordic there, that it needs to be better explained...?

[Jørgen Holmefjord]

awneil said:

However, in this case, I would have thought you would have got compile errors?

As long as the header file where the function is declared is included, you will not get compilation error. If header file is included but source file is not included in project, you will get this linker error.

awneil said:

this one is a frequent cause of confusion - so maybe there's a clue for Nordic there, that it needs to be better explained...?

I think it is explained well in the documentation:

"Every module in SDK contains at least one configuration option that enables this module. If the module is disabled, then even if source code is added to the project, it is not compiled because the module implementation is conditionally included."

I will say that is should be expected of customers to read through the Getting Started section of the SDK documentation to get familiar with the SDK before starting to develop applications.

[awneil]

Jørgen Holmefjord said:

I think it is explained well in the documentation:

"Every module in SDK contains at least one configuration option that enables this module

I didn't find that it was always easy to identify what configuration option(s) is/are required by a particular module.

Especially as some (many? most?) modules have dependencies on other modules.

Plus the added confusion of there often being NRFX and "legacy" versions of the same thing ...

eg, see: https://devzone.nordicsemi.com/f/nordic-q-a/39469/linking-mpu6050-sensor-with-ble-uart/152957#152957

See also: https://devzone.nordicsemi.com/f/nordic-q-a/34739/how-to-add-simple-timer-to-a-project/133302#133302

[awneil]

and why does the forum quote feature keep going wrong like that - ie, the quoted text is outside the quote marker!

[Jørgen Holmefjord]

I agree that dependencies could have been documented better, but this is more related to the modules themselves, rather than the sdk_config.h file. You still needs to include the source files of the dependent modules.

It might take some iterations to add all sub-modules that a module depends on, but the compiler will give you hints to what needs to be included/enabled.

[awneil]

Jørgen Holmefjord said:

this is more related to the modules themselves, rather than the sdk_config.h file

Indeed.

But see my linked thread - I didn't see anywhere that told me what files I needed to include!

Jørgen Holmefjord said:

the compiler will give you hints to what needs to be included/enabled

Indeed - but we're back to development by reverse-engineering again.

We shouldn't have to discover this stuff by trial & error - it should be clearly documented up-front.

[Jørgen Holmefjord]

Like I said, I agree that this is not well documented. We have an internal task requesting more documentation on library dependency documentation.