Now works even when the CPU is stuck in a watchdog reset loop, as it would be when the flash is totally blank.

CSW at this point isn't valid if the error wasn't a timeout but it was something else instead, like a FAULT.

Working on making this reliably halt a chip that's stuck in a watchdog reset loop :(

That was a silly library, full of middleware and memory leaks. Debugging libswd was a good way to get familiar enough with SWD to write a replacement really quickly :P

This still doesn't work reliably, it seems to have the same unsynchronization bug that the old code was having. But it's much smaller and easier to understand now!

Some silly bugs are undoubtedly lurking here, but sometimes this will successfully read and write target RAM :)