It's useful to know when only default USB power is available, as opposed
to when some mechanism for negotiating higher power is available but it
isn't possible to get high enough power. This can let users know e.g.
using a USB A to C cable can't provide high power, potentially reducing
confusion.
The blink code for this is 1 7/8 s on, 1/8 s off. I think this is
sufficiently unlike other blink patterns that it won't cause any
confusion.
The GUI will have a button to identify a particular PD Buddy Sink, in
case several are connected to the computer at once. The button will
cause the LED to blink quickly for a couple seconds, then go back to
normal. To allow this, I added a new LED blink mode (FAST_BLINK_SLOW)
that causes 8 fast blinks, then returns to SLOW_BLINK mode. A new
"identify" command triggers this LED mode.
There are still a few things that the standard says we Shall do and we
don't, but it Works For Me™. I haven't implemented anything with
regards to GiveBack support, but that doesn't matter just yet. Our
handling of VDMs isn't quite right either. Anyway, it successfully
negotiates with so-called Split PDO power supplies, which is more than I
can say about some commercial products.
Clara Hobbs