The datasheet of XE216 mentions:
So, the question is: where is this pin ? They is nothing about it on the datasheet, and no pull-up in the ref design schematics.The xCORE Tile boot procedure is illustrated in Figure 8. If bit 5 of the security
register (see §9.1) is set, the device boots from OTP. To get a high value, a 3K3
pull-up resistor should be strapped onto the pin. To assure a low value, a pull-down
resistor is required if other external devices are connected to this port.