On: Apple Lightning

[cortesoft]

Why wouldn't the device ask the port directly? A chip in the cable means that the device asks the cable, which then asks the device.... why not cut out the middleman?

[derefr → cortesoft]

One use-case comes up in the article: the chip in the cable is able to probe information from the device even when the device is unpowered, essentially acting as a microcontroller grabbing some of the device's less-guarded peripherals for itself.

[WrtCdEvrydy → cortesoft]

If the device is dead, then it can't ask the port.

This is also tied to fast charging (and whether the device will support it)

[cortesoft → WrtCdEvrydy]

Couldn't it provide the low power until the device is powered enough to answer the fast charging question?

[cortesoft → WrtCdEvrydy]

Also, wait... if the device is dead, how does the CABLE know that fast charging is supported by the device?

[warricksothr → cortesoft]

I think the link describes this tangentially. The minimal 10mw - 15mw current that high-five allows on a cable that hasn’t completed a handshake is enough to charge the capacitor for secure boot and trident which then can handshake with 0x74 to receive 5v 1a source. When the kernel boots the rest of the handshake process can be completed to increase the current.

That’s at least my understanding from the document.