Q: Cannot upgrade Thunderbolt firmware on mid-2011 iMac

Hi - I'm having problems updating the Thunderbolt firmware on my mid-2011 iMac (21.5").

Can anyone point me to the proper location for this firmware download? I've found several on the site, but none seem to work for me, due to a variety of OS incompatibilities.

For the curious, here's what my system says:

Hardware Overview:

  Model Name: iMac

  Model Identifier: iMac12,1

  Processor Name: Intel Core i5

  Processor Speed: 2.7 GHz

  Number of Processors: 1

  Total Number of Cores: 4

  L2 Cache (per Core): 256 KB

  L3 Cache: 6 MB

  Memory: 12 GB

  Boot ROM Version: IM121.0047.B1F

  SMC Version (system): 1.71f22

Thunderbolt Bus:

  Vendor Name: Apple Inc.

  Device Name: iMac

  UID: 0x0001000A15928E80

  Route String: 0

  Firmware Version: d.16 (Eng 1)

  Domain UUID: 78CF7309-6B81-CC54-A320-6D5B13722358

  Port:

  Status: No device connected

  Link Status: 0x7

  Speed: Up to 10 Gb/s x2

  Receptacle: 1

  Port Micro Firmware Version: 1.2.1

And here are the error messages from a variety of firmware update locations:

Thunderbolt Firmware Update v1.2

First error: The package was signed with a certificate that has expired (c'mon Apple!)... Do you want to continue with the installation anyway? (yes!)

Second error: Alert: This software is not supported on your system. (any reason why? OS, old other firmware, what?)

I've tried the tricks of PRAM and SMC resets, moved the com.apple.SoftwareUpdate.plist to the desktop and rebooted, etc., etc., but nothing seems to work.

The issue driving this exploration is that the Thunderbolt port appears to be dead - won't support Target Desktop Mode or the Thunderbolt Gigabit Ethernet adapter.

Thanks in advance for any help!