timestamp: Add function to get time since boot

Add a function to retrieve the elapsed time since boot. For that purpose
use the base time in the timestamp table among with the current
timestamp at call time of the function. So more precise the returned
time is the elapsed time since the timestamp was initialized scaled
in microseconds. This was chosen to get a reliable value even on
platforms where the TSC might not be reset on software reset or warm
start.

Change-Id: Ib93ad89078645c0ebe256048cb48f9622c90451f
Signed-off-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-on: https://review.coreboot.org/21516
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

0 files changed, 0 insertions, 0 deletions