I want to use a CH340G USB UART to connect to the console of my raspberry pis - something like this: http://www.ebay.com.au/itm/To-TTL-USB2-06Pin-CH340G-Converter-for-STC-Arduino-PRO-Instead-of-CP2102-PL2303-/191149156465 (sorry for the ebay link, but I could not find anything more permanent. Please comment if you have such a link).
Hooking up TxD, RxD and GND are easy. I want to be able to use the DTR signal to reset the RPi. If I turn on DTR, I want that to go to a pin that will cause the Pi to reset. This makes this little USB UART useful as a low-level device access mechanism, accessing the serial console (and with u-boot, it can hook into the boot process), and a reset line if things go bad.
I do not want a user- or kernel-level mechanism to detect this and do the reset. I'd like it to be at the hardware level so I can reset at any time regardless of the state of the software.
I also do not want to use a watchdog. I would like a crashed Pi to keep its last error message on the console and allow me to reset manually.
How can I hook up the DTR line to do this?
Edit: I have RPi Model B rev 2.0 and RPi2 boards.