This second post further details the protocol errors with the +Nintendo Switch, in particular with the Apple 61w USB-C power adapter.

Further bad news: the Apple 61w adapter, due to its nonstandard voltages, exposes some very untoward behavior with the Nintendo Switch dock. You'll get a 'Use OEM adapter' killscreen.

All the protocol errors I described previously are still present. However now there are some more, owing to the fact the Apple 61w adapter lacks a 15v voltage profile. Note in the traffic dumps how the Nintendo dock "passes through" the 9v/3a profile instead.

The key point to note is the DISC_ID command reply changes. The Switch dock no longer claims it is an "Alternate Mode Adapter" dongle. Instead it chooses to identify as an "Undefined".

This introduces a few new errors:

* First, the dock is no longer permitted to respond with a "Product Type" VDO field to a DISC_ID query. But it does anyway, in direct violation of the USB-PD spec. ("Shall.")
* Second, (likely because the Switch dock doesn't flag itself as an AMA anymore,) the Switch tablet doesn't initiate a DISC_SVID query.
* Third, the dock no longer claims to be able to enumerate as a USB device.

The second point is important since the DISC_SVID would ordinarily expose the DisplayPort and "Nintendo" AltModes. Once the DP AltMode is exposed, it can be entered into, configured, and you get video out.

Yet the dock still "jumps the gun" and enters "Nintendo" AltMode. This is extremely odd. Somehow the dock circuits are powered on enough to have one AltMode components powered, but not the other. DisplayPort isn't exactly power intensive...

The above two "weirdnesses" combine (Switch knows its in a Nintendo dock, but it can't see a DisplayPort mode available) and bingo -- the Switch throws a VERY unique error:

"Could not connect to the TV. Please make sure that you are using the AC adapter supplied with this console."

I have yet to test with other supplies, such as a 30w USB-PD power rules abiding one. But this data suggests the internal circuits are live and powered even at 9v. Without doing a teardown and looking at the voltage traces and ICs I won't be able to say for sure. But from my limited knowledge, it is quite atypical for ICs to run off 12v Vcc. (Usually it is 5v or 3.3v, or at worst variable voltage input.)



In summary: this tells me Nintendo could have made changes to allow the dock and Switch to run with power supplies less than the "required" 39w. Nintendo just opted not to do it. This was likely for continuity of experience. (People wouldn't like laggy fullscreen play if there wasn't enough spare power to overclock the Switch GPU.)

I still think Apple has the more elegant approach: let people at least use weak power supplies while doing heavy processing with their MacBook Pro. Nintendo could have had a dynamic GPU overclock depending on the input wattage. But that type of extra engineering is a lot harder than simply saying "use a 39w PSU or better".

More details to come, as I uncover them.

#USB #TypeC #USBC #NintendoSwitch
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5/29/17
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