diff --git a/source/chapter1-about.rst b/source/chapter1-about.rst index e424214d64644af6bee1fd06820764df0c2ac878..3b5b38e3a76ff5cd7db404ad60c8df486f8d62a7 100644 --- a/source/chapter1-about.rst +++ b/source/chapter1-about.rst @@ -67,6 +67,9 @@ Assumptions components and multiplexing boot combinations can be very challenging. In this document we treat the firmware as a single entity regardless of the components it comprises. Failing to update one of the components will lead to rollbacks of every affected component +- Updating the firmware and the OS at the same time is prohibited. +- A hardware watchdog must always be active at least in BL33. It's advisable + the watchdog is activated on earlier boot stages as well. .. [#UEFICapsuleUpdateNote] [UEFI]_ 2.8B ยง 23 - Firmware Update and Reporting @@ -112,6 +115,12 @@ during an update. If the secondary partition contains a valid firmware and the is unable to boot the device (e.g flash corruption), the device is allowed to fallback on the secondary partition. +If the update is going to update the rollback counters it's strongly advised to update both of the +partitions. In that case the upgrade process will run once to update the secondary partition. Once +that's finished and accepted, the firmware update agent should update the former primary partition +as well. This process must not necessarily go through the entire update procedure. Simply writing +and verifying the firmware is enough. + .. image:: images/rollback_protection_simple.png :width: 200px :align: center