Erin 💽✨ @erincandescent@akko.erincandescent.net
Public

So the basic USB PD sequence is

  1. Source: Source_Capabilities { 5V3A, other possible capabilities}
  2. Sink: Request { 5V1.5A }
  3. Source: Accept
  4. Source: PS_Rdy

I spent the entire day trying to work out why the source (my laptop) didn’t like my Accept message. It was bitwise identical to what I saw other hardware sending, so I didn’t understand why it disliked it. I added all sorts of debug logging to track it down.

The problem turned out to be that my stack was too slow, on account of all of the debug logging. A good old embedded systems classic.

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