2012 MacBook Air - USB hardware ran out of device slots? I've got a 2012 11" i7 MBA. This is a great little machine but one thing has been driving be absolutely batty about it... The USB ports work well for the most part, but inevitably I will plug in a USB device (could be anything. Thumb drive, USB serial port, JTAG cable, USB2 or USB3 device, doesn't matter) and it will power up (LEDs blink, etc.) but the device is not recognized by the Mac.

Looking at dmesg, I see this:

USBF:    126826.226    AppleUSBXHCI[0xffffff80d5636000]::WaitForCMD (Enable Slot Command) - Command failed: -1009 (num interrupts: 93582187, num primary: 46791094, inactive:0, unavailable:0, is controller available:1)
USBF:    126826.226    AppleUSBXHCI[0xffffff80d5636000]::PrintInterrupter WaitForCMD IRQ:0 - IMAN: 00000002 IMOD: 000700a0 ERDP: 002043d0
USBF:    126826.226    AppleUSBXHCI[0xffffff80d5636000]::UIMCreateControlEndpoint 2 - Run out of device slots, returning: e0004045
USBF:    126826.226    AppleUSBHubPort[0xffffff8015ddce00]::DoConfigureDeviceZero  Port 1 of hub at 0x14000000.  Cannot create USB device (kIOUSBDeviceCountExceeded)
The USB stack is not able to enumerate the device at Port 1 of hub at 0x14000000 because the USB hardware ran out of device slots


At this point the USB port is kaput. Unpugging/replugging the same device or another will show similar messages. The only solution seems to be a reboot. Putting the Mac to sleep doesn't help.

I've got the USB logging driver installed to try to help diagnose the issue but I am not seeing anything that I could call a smoking gun, and trying to reload the USB kexts does not help either.

This issue was present on my old 2011 MBA as well, and the issue has persisted from 10.7 to 10.9. Both ports will eventually do this, which makes me believe that it isn't a physical port issue since one port is on a separate I/O board and the other is on the main logic board. I've tried to connect the device through an external USB2 and USB3 hub (tried both) and the problem will eventually occur in these situations as well.

I'm fairly technically savvy, but not necessarily at my best on OSX. I can gather more information if someone were to help me determine what data is appropriate to help debug the problem. I've also done the usual NVRAM/SMC resets, fix permissions, etc... doesn't help.

Has anyone else run into this? What information could I provide to help diagnose the issue? Does anyone know of a way to fully reset the XHCI controller in this situation to try and recover without needing the reboot?

Edit 20140217

Adding the bounty certainly got this question the attention I felt it needed! Thank you for all of the answers so far, but I think that there are some important misconceptions that I'd like to address:


I didn't migrate my account from the older MacBook Air. Brand new install
The problem occurs with pretty much any device. USB keys (no cables here!), JTAG adapters, USB3 drives
The problem occurs with or without USB2 or USB3 hubs
If the problem occurs with a device on a hub, unplugging the hub and plugging the device directly into the Mac doesn't help
If the problem occurs without a hub, plugging the device into a USB2 or USB3 hub doesn't help
Once the problem occurs, logging out / switching to a different (new) user doesn't make the problem go away for the new user or the old user.


I develop electronic hardware and software for a living, including USB 3.0 devices. I'm familiar with USB root port drivers, but not at all familiar with low level (kernel) development on OSX.

I'm fairly certain that this is a device driver problem simply due to the nature of how it manifests itself. From a clean boot, things work great. Unplug/replug and it might still work great. Unplug/replug will eventually cause the problem to show up, and at that point ANY USB device in that port will not work. Reboot and things work great again.
Good news: you don't have any problems with your hardware. Or software, permissions, etc.
The issue is, believe it or not, exactly what the error message says:

the USB hardware ran out of device slots

You're probably under the impression that something like 127 USB devices can be used
with a single controller, since that's what all the marketing material says. But that's actually only true in a single very specific and probably mostly theoretical configuration. USB devices support, at a maximum, five connections in a tiered-star hierarchy. Hubs are not passthrough devices, so they count against this number, as do any internal components which use the USB bus, and any devices which use more than one device profile (even if it's only a single physical connection).
How could I know you don't have a problem with your hardware though?
Why, because I have the same machine, and I was able to reproduce the error!


If the issue seems to be sporadic you're probably running into a couple of other issues too:

Crappy, incompatible chipsets in hubs, since the standard has no enforcement.

Insufficient power: faster USB speeds require more power than slower ones.
If a device has the ability to fall back to a slower speed (rather than error
due to insufficient power), it will do so, taking anything on the same bus with it.


If you don't want to see this error again:

Throw out any USB hubs and cables you are currently using. Dead serious.

Drop the $40-$80 for two to four of these, plus however many of these you need.
Most USB 3 cables should be fine.

Especially considering all the devices you mention are high-speed and not
very error tolerant, you should never rely on bus power, and make sure the  (Yep, a wall wart for each hub and device. Exceptions: keyboards, mice, etc.

That last point is especially true on the 11' MBA, which ships with a measly 45W power adapter, and the computer basically needs all of that even with only a moderate CPU load. If you have this cash, consider buying a 60W or 85W adapter.

In practice max, devices/hub connected on a single hub is 2 + another hub.

Always use 4-port hubs, not 7-port. 7-port hubs are just two controllers in a chain.
But you don't know which ports connect to the first hub or the second!
(Without looking in System Profiler.)

If in doubt, prefer the USB port on the logic board (right). There's a remote possibility there's interference in the I/O board. Luckily, that isn't an expensive part.


Follow those steps and I basically guarantee this issue will go away.

Edit: the hardware/kernel development perspective
To answer to the clarification that this is a developer question.
So: The log snippet posted does indicate what I addressed above: too many USB 3.0 devices connected to the root XHCI hub.
(The QS77 chipset supports 4, and there are 2 in use inside the machine.)
To &quot;reset the XHCI controller&quot; (technically its a kernel, not controller, issue):
sudo kextunload -b com.apple.driver.AppleUSBXHCI
sudo kextload -b com.apple.driver.AppleUSBXHCI
however, that's not going to do anything if this is happening with USB 2 devices as well, in which case that its:
sudo kextunload -b com.apple.driver.AppleUSBEHCI
sudo kextload -b com.apple.driver.AppleUSBEHCI
and if its both, well, neither of those.
When I say I can reproduce the issue, I mean that if I overload the XHCI bus like in the log snippet, I get the same error message. And I wasn't assuming necessarily you were using a bad hub — it equally that you might need to get a good one, because the root  hub has too many connections.
Beyond that, however, I think we're getting into the realm of a wiki question to the effect of:

How do I debug the kernel and device drivers on Mac OS X?

As thats more the issue, nothing to do with the MacBook Air per se or even necessarily USB.
I might try my hand at writing one (not really my expertise but I've done it a few times) But it'll probably be a few days for that. Meanwhile, take a look at:
man 8 kext_logging and sudo sysctl -w debug.kextlog=0xlogspec
kextstat | grep USB
The IOUSBFamily source.