There are several criteria for DPF regen
1) soot loading: This is usually the limiting factor and what triggers regen most (all) of the time. It is determined 2 ways, Measured soot and calculated soot. Measured soot comes from the d/p sensor. Calculated soot comes from the ECU's internal model, based on time and how much load is on the engine. You can see both of these numbers in VCDS. One thing you will likely notice, "calculated" soot is usually higher than "measured" soot. if you pay close attention, you will also see that "measured" soot can increase, and also decrease due to passive regen starting at ~350-400C. But "calculated" soot only increases with time and proportional to load. You will also recognize that regens are only triggered on "calculated" soot load. This is not only because the number is usually higher, but the ecu developers deemed it "more accurate". In the EA288 cars the trigger is set at 24g.
2) engine operating time: in this application the time is set to an impossibly high number like 32767 minutes of engine run time, so it will never trigger a regen.
3) Distance between regens, set at 750 km.
4) Fuel burned, setpoint is ~120 liters. About 30 gallons, so at 40 mpg that works out to about 1200 miles.
Each or any of these criteria could trigger a regen. Usually, it ends up being the dpf soot loading because that ends up being way more conservative than the other trigger points. After regen these counters are reset to zero.
DPF pressure reading is in hPa or millibar. So when you see 300 it is NOT 300 PSi, but 300 mbBar... more like 4 psi or so. 1 Bar = 14.7 psi