The term "backend" can be confusing because it can refer to both the
virtual function table and the device/parser backends. The use of the
term "vtable" avoids this.
The Petrel is slightly different from the Predator because the device
reorders the internal ringbuffer before sending the data. The most
recent dive is always the first one, and there is no need to search for
it, like we have to do for the Predator.