I found quite a few answers when watching this https://www.youtube.com/watch?v=ijTTZgQ8cB4  "Flying autonomous aircraft: Mixed-criticality support in seL4" (and of course the main landing page https://ts.data61.csiro.au/projects/TS/realtime.pml )

From: Devel <devel-bounces@sel4.systems> on behalf of Isaac Beckett <isaactbeckett@gmail.com>
Sent: Wednesday, February 5, 2020 15:15
To: devel@sel4.systems <devel@sel4.systems>
Subject: [seL4] Question about MCS branch
I have a bit of a noobish question, why are timing/scheduling abilities being added to the kernel? I understand that userland still controls scheduling, regardless of which branch is being used, but I'm confused as to wby scheduling features needed to be added to the kernel itself.