The current draw for charging has to be done through software. As indicated, based on the specs and info provided by evolv, if it draws more than 500mA when data lines are present it is malfunctioning.
You keep talking about having the connected device protect the supply and I keep telling you the supply is supposed to be engineered to protect itself as well as the device. Much more can go wrong with what's connected to a USB port than drawing over 500mA -- as mentioned a shorted 10c cable will do the trick. If that fries a supply or bus, it deserves to die. So to answer your question, no, the device side of a USB interface should not be required to have a completely fail safe overcurrent protection system built into it because doing so is 1. Impossible (the failure could be upstream of the device, such as in the cable) and 2. Wasteful because a truly fail safe system where device current draw is programmable would be relatively expensive on the device end. On the supply end, it can be much cheaper to design a true fail safe because the supply has a fixed absolute max current it is designed to deliver in addition to the fact that one supply is intended to connect to a number of devices. As an example, a good hub design would have one of these at each port: Fast-Tripping Resettable Fuses Can Protect USB Circuits
I don't know where you keep getting I'm asking about protecting the supply but your misunderstanding my questions. In fact one of the re-posts in the original post the PC did take appropriate measures and prevent damage to the PC when the malfunctioning DNA 200 was connected, so I understand in some cases the connected PC may prevent Overcurrent when the DNA doesn't. My questions are mainly regarding the DNA board and what Over Current Protection it had if any. I've found another post that appears to answer several of my questions that I'll post with my original questions again.
I don't see anything in the data sheet that indicates there's USB Over Current Protection.
So this makes me wonder do these boards have USB Over Current Protection? (based on the attachment it appears there is)
Shouldn't they if they don't? (based on the attachment it appears it should)
If they do what could explain these examples? (This is the main question now)
If they do is it only mechanical in nature? As in by utilizing only the electronic components?
Couldn't there be USB Over Current Protection logic programmed into the firmware? I don't think there is since mine appears to work as designed and some of the others appear the CPU is functioning and communicating via USB with the PC and Escribe but no software restrictions appeared to be activated when they were charging above 500mA while connected to PC.
What about circuit isolation, couldn't there be isolation so if a component failure does occur it could be rendered inoperable or as an open circuit so as not pull more current than it was designed for and potentially damage the source charging power source?
(I think I see the portion of one of my questions that may have lead you to believe I was asking about the source. I'll leave that as is since not all pc's in use have the same protections but I'll bold the preceding portion to be more obvious to that question.)
So believing these boards are supposed to limit current to 500ma when connected to PC and that there is Overcurrent Protection built in, and the ease of finding similar malfunctioning devices like was in the original post.
This brings up other questions in regards to some other reported problems like boards or USB chips getting hot when connected to PC. Since it's clearly not isolated to just a couple devices that are charging over the stated current limit it seems logical the other reports of boards or chips getting hot when connected to PC could be due to similar malfunctioning boards or the inadequacies / failures of the Over Current Protection as well. Even a resettable fuse like you linked earlier would have provided some form of protection to the board of the poster that was showing charging at a little over 3 amps.