Background
I sometimes find that the frontmost of three ports on a 2009 MacBookPro5,2 is less capable than the other ports.
This frontmost port with an independent bus seems:
- good enough to charge an iPhone 1
- sometimes problematic for devices that have their own power sources
- sometimes problematic for simple bus-powered devices, for example a Microsoft IntelliMouse Optical.
Maybe more problematic when the laptop is booted from something other than the internal drive (Serial-ATA).
In some problem situations, reconnecting the device to an alternative port might work around … at least temporarily.
I read of comparable problems with:
Expectation
One port should provide up to 1100 mA at 5 V subject to the conditions given in Apple article HT4049.
Question
Why might just one USB port of a MacBook Pro be problematic with a device that draws little power, or with a device that has an independent power supply?
Environment
MacBookPro5,2 with 8 GB memory, checked twice with Apple Service Toolkit (AST) by an Apple authorised service provider.
To the best of my knowledge/recollection:
- when I find trouble with the frontmost port, neither of the other ports has requirements exceeding 500 mA at 5 V
- I have no device that requires more than 500 mA.
Rearmost port
USB High-Speed Bus:
Host Controller Location: Built-in USB
Host Controller Driver: AppleUSBEHCI
PCI Device ID: 0x7f8b00000aa9
PCI Revision ID: 0x7f8b000000b1
PCI Vendor ID: 0x7f8b000010de
Bus Number: 0x26
Central port
USB High-Speed Bus:
Host Controller Location: Built-in USB
Host Controller Driver: AppleUSBEHCI
PCI Device ID: 0x7fb200000aa9
PCI Revision ID: 0x7fb2000000b1
PCI Vendor ID: 0x7fb2000010de
Bus Number: 0x26
Frontmost port
USB High-Speed Bus:
Host Controller Location: Built-in USB
Host Controller Driver: AppleUSBEHCI
PCI Device ID: 0x7250505300000aa6
PCI Revision ID: 0x72505053000000b1
PCI Vendor ID: 0x72505053000010de
Bus Number: 0x24
Always on bus 0x24: the built-in iSight, which requires 500 mA when not in use.
Other buses
USB Bus:
Host Controller Location: Built-in USB
Host Controller Driver: AppleUSBOHCI
PCI Device ID: 0x7faf00000aa5
PCI Revision ID: 0x7faf000000b1
PCI Vendor ID: 0x7faf000010de
Bus Number: 0x04
USB Bus:
Host Controller Location: Built-in USB
Host Controller Driver: AppleUSBOHCI
PCI Device ID: 0x7faf00000aa7
PCI Revision ID: 0x7faf000000b1
PCI Vendor ID: 0x7faf000010de
Bus Number: 0x06
Links
How do you check how much power a Mac USB port can deliver?
Apple Computers and Displays: Powering peripherals through USB – article HT4049.
Some time after posting this question I learnt that USB is amongst the focus areas for Build 12B13 of OS X 10.8.1. I'll review this question, and answers, after 10.8.1 is released.