All of the GPIO pins support both analog and digital signals. Analog signals must be limited from 0V to VDDIO (nominally 3.3V), and band-limited to 50MHz. The Caravan chip is meant to accommodate analog signals outside of that spec (mainly high voltage, negative voltage, or high frequency). Your control signal is perfectly well suited to connect to the GPIO pin. On the user wrapper, connect to the

analog_io

pins, and note that due to a different indexing system,

analog_io[0]

corresponds to GPIO 7 (that is, you are not allowed to use the lowest six GPIOs for analog signals). The management SoC program that initializes the GPIOs should set the GPIO mode for that pin to analog (configuration word

0x000a

otherwise known as

GPIO_MODE_USER_STD_ANALOG

).