Mac Pro EFI Firmware Update

Mac Pro EFI Firmware Update 2.0... This update is recommended for all Mac Pro (Late 2013) models. This update improves system reliability during reboot, resolves an issue with memory self-test, and improves graphics power management when using Boot Camp.
To complete the firmware update, wait for your Mac Pro to finish installing and shutdown.

Hold down the power button until the power indicator light flashes, or you hear a long tone, then release the power button. A gray screen with an Apple logo and progress bar will appear while the update is taking place. When the update is complete your Mac Pro will startup normally.