No, this isn't using SWD on a Teensy 3.1 (which would be nice)...it's making the Teensy into a SWD dongle!
NOTE: This project is in progress
So, I have a chicken-and-the-egg problem. I assembled one of my [kl2-dev board] (https://github.com/kcuzner/kl2-dev) prototypes and then realized that I needed some way to load the initial bootloader on to it. I had realized this before, but I never got around to actually doing something about it until now.
There are other options for this such as buying a JTAG dongle, using one of the FRDM boards, or using the CMSIS-DAP loader, but those require either purchasing new hardware, modifying hardware or porting things to new chips. Thus, it will be easier/cheaper for me just to write a simple program that can execute SWD commands (possibly in a scripted fashion).
This project is the host and firmware for a USB to SWD adaptor. The objective is that the host program should be able to take an intel hex or elf file and issue the appropriate SWD commands via USB to program that program into the device, so long as it lives in RAM.
Alternately, I could execute the flash write commands directly from SWD, but that could be super super slow. I imagine that I will have some sort of bootstrap program which writes up to 1K (or some amount) to the flash from some data that I have previously loaded via SWD into a specific location in RAM. The SWD will then be used to poll another specific memory value to see when the program has finished writing its flash.