USB charging, part 1: requirements [LWN.net]

USB charging, part 1: requirements

Posted Jul 11, 2016 0:35 UTC (Mon) by giraffedata (guest, #1954)
In reply to: USB charging, part 1: requirements by neilbrown
Parent article: USB charging, part 1: requirements

OK, 2.5mA is really niggardly, but what about 100 mA for a second? Isn't that enough time for a boot loader to come up and enough to negotiate more?

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USB charging, part 1: requirements

Posted Jul 11, 2016 10:13 UTC (Mon) by neilbrown (subscriber, #359) [Link]

1 second is certainly enough for a u-boot to be loaded and do something useful. I don't know if it is long enough to complete usb negotiation, but I suspect it is.
But for many processors, 100mA isn't enough to execute any instructions, let alone load the boot-loader from nand-flash which is most likely where it is. There maybe be some Linux-capable platforms which can run the boot-loader with only 100mA, but I doubt they are common.