This project is a basic example of how to connect to an XBox wireless controller and read the HID reports it emits on the HID interrupt channel using the Raspberry Pi Pico W and btstack.
When the pico first boots, it will start scanning for joystick class input devices (0x000508), and if it finds one named 'Xbox Wireless Controller' it will attempt to connect to it.
I used examples from bluepad32 and bluekitchen/btstack#464 to help figure out the flow for pairing to a device and establishing l2cap channels.
General flow when pairing a new device seems to be: gap_inquiry -> device found -> gap_name_request (if not provided in inquiry response) -> gap_dedicated_bonding -> l2cap_connections
After dedicated bonding, the device will make an hci_connection_request when powered on, using keys exchanged during dedicated bonding to authenticate. Then the l2cap_connections will be established for the HID control and interrupt channels. The HID reports will be sent using the interrupt channel of the device