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I don’t think they can avoid a usb device stack in bootrom. I haven’t read about this much yet, but without bootrom USB device mode support, the BL can’t be fla
by uxp100 7y ago
I don’t think they can avoid a usb device stack in bootrom. I haven’t read about this much yet, but without bootrom USB device mode support, the BL can’t be flashed on a bricked device. So, devices that are functional still, but somehow corrupted couldn’t be fixed in an Apple Store (or at home?). They’d likely be trash.
I’m sure they have multiple redundant BLs, so I don’t know how often this actually happens.
That USB code was surely the riskiest thing in the bootrom by far though. They will be re-evaluating if it is necessary in new chips.
They also probably provision the devices with USB in the factory. But if that’s all the usb was for, I would suspect it would be disabled as the last step.
- dev_dull 7y agoCouldn’t they use some other wire format that simply uses the same port?
- uxp100 7y agoSpeed is a concern in the factory, and that would slow them down even if the alternate format was as fast as USB, which it probably wouldn't be. USB pads could be special and require additional work to mux with whatever the other format is. There are things they could do at the software level that could make sanitization easier too. But if they are really upset about this, they will consider it.
- kirb 7y agoApple actually used to do this on MacBooks - one of the USB ports has mux circuitry that can be switched to an SMC programming mode that merely uses USB as the physical connection for their SMC programmer tool, bypassing the USB host controller and not using the USB protocol. It was removed in the 2016 onwards MacBooks as the T1/T2 supersedes the SMC, so it follows the same design patterns as iPhone hardware.