I upgraded yesterday to the recent version of microcode-data. However, on next boot, the microcode_ctl service could not start because of a missing file. After upgrading to the latest testing version, the service started fine. I suggest that the microcode-data ebuild depends on the testing microcode-ctl-1.17-r2, because it could confuse users.
you cant depend on it because microcode-ctl already depends on microcode-data. circular dependencies dont work. microcode-data-20100209 now has the blocker