Home Forums Hardware Mac Desktops & Notebooks Resetting a laptop's ports

I was dealing with a situation that seemed (albeit by a long stretch) like it may have had something to do with a wonky FireWire port, so I dug out instructions (posted by joemikeb ??? years ago) for resetting a laptop's ports, but they're outdated, because they call for yanking the battery, which can no longer be done.

Is there still a way to reset a laptop's ports in the absence of the ability to completely power down the machine?

Searching has been fruitless.

Thanks.

despite having a non-removable battery, there has always been a PMU/SMU/SMC reset procedure on all macs. You'll have to look on apple's web site for instructions on your model. It usually involves unplugging ac power, shutting down, and then holding a very specific set of keys down, which varies slightly from model to model.

Just did that the other day, as a matter of fact. (Could it have affected my battery?)

These are joemikeb's instructions:


Does resetting SMC accomplish the same thing?

The SMC is one of the microcontrollers that's always running on your mac, even when it's off. It controls several aspects of the computer that need to be running while the computer is off. Things like scheduled turn on, turning on the computer in response to pressing the power button or restoration of AC power, as well as things like Wake on Magic Packet and Lights Out Power Management. It also manages the computer busses which need to be running to some degree while the computer is off. So USB and Firewire controllers and devices sometimes require SMC resets if they get jammed - simply powering down the computer doesn't reset them. Since so many of the computer's systems rely on common busses rather than dedicated connections, SMC reset is a fairly useful fix-all to try when something isn't working, whether it be a firewire port or the camera in the display panel.

AAAARGGGHHH! Who would have thought that advice offered all those years ago could come back to haunt me?

In the last few years many, perhaps most, of our long treasured sovereign remedies for all problems Macintosh have become deprecated, obsolete, or have disappeared altogether. I have tended to think about those mostly in terms of OS X changes, but as Artie505 has pointed out there are hardware related changes as well. If things keep changing this fast, FineTunedMac might have to consider following the lead of the Apple Discussions with separate forums for each OS version and hardware model. (Hopefully that will not be necessary.)

I am not even sure I can remember all of those sovereign fixes we used to think were so invaluable. Even if I could remember them all I am way too lazy to attempt to go back and annotate the myriad of posts made over the years to post out which work in what versions of software or on what model Macs, iPods, iPhones, or iPads.

In response to Artie505s specific query
Whether or not resetting the SMC discharges the capacitors in all the various ports or that is even necessary in newer Macs — it is about as close as you are likely to get.

Well I can tell you for certain it does not discharge capacitors. It triggers a forced reboot of the microprocessors. There is a dedicated RESET line on them that when that one goes high etc, causes an unstoppable, uninterruptible chain of events that leave the processor back in its default state before triggering the bootstrap, regardless of what it happened to be doing or how badly deadlocked it happened to be.

cliff notes:
- STOP the master clock (abruptly halts all CPU activity)
- clears all registers, interrupts, and other processor status flags
- clears all pointers, resets all vectors and JMP tables to their default addresses
- loads the program counter with the INIT (bootstrap) routine's address
- restarts the clock

Note this isn't the state it's in when its cold-started. Cold-start usually triggers the above RESET process. A simple example is on the 6502 processor. The Reset Vector's default memory values on power-up insure a checksum mismatch. When the system comes up, it triggers the hardware level RESET, which loads different values due to the reset vector being invalid, loading the PC to point to the Reboot program before restarting the clock.

BOO!

At least I didn't try to yank the battery.