The CC2511 data sheet says that the ADCCFG register should be set in order to make the P0 pins ADC inputs. I don't see any reference to ADCCFG in the ADC library, so I thought I'd bring this up.
I agree that the SDK/library documentation should mention that one is expected to initialize the ADCCFG register prior to using any ADC library function. Even the included examples in the SDK ignores ADCCFG configuration.
Thank you for bringing this to our attention. I have updated the documentation for adc.h to mention ADCCFG. The CC2511F32 datasheet does not say exactly what happens when you set a bit in ADCCFG, and we have not found it to be necessary. If anyone finds that the settings in the ADCCFG register makes a measurable difference, we would be interested to know what it is.