What is the ADC_KEY_IN1 function?


What is the function of the ADC_KEY_IN1 pin? From the RK3308 datasheet, there are 6 single ended ADC pins, but only 2 are exposed to the GPIO header. I would like to use 2 ADC pins, can ADC_KEY_IN1 be used the same as ADC_IN0? or does ADC_KEY_IN1 serve a different function?