One of the main architectural points of note with Zynq-7000 devices is that the boot
method is restricted to a single source — device boot must be driven by the processor.
When the device is powered on or reset, the first core of the PS boots from external
memories before going on to configure the PL [28]. By restricting the boot method to a
single source, it ensures that the there is no manual way to load malicious software after the
PL has been configured, and also no way to load a malicious image to the PL after the
processor has initialised.