doc: tweak hld intro

Add another level to the HLD toc, and start conversion of the HLD intro

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/developer-guides/hld/hld-overview.rst

@@ -1,4 +1,58 @@
 .. _hld-overview:
 
-Overview
+ACRN high-level design overview
-########
+###############################
+
+ACRN is an open source reference hypervisor (HV) running on top of Intel
+Apollo Lake platforms for Software Defined Cockpit (SDC) or In-Vehicle
+Experience (IVE) solutions. ACRN provides embedded hypervisor vendors
+with a reference I/O mediation solution with a permissive license and
+provides auto makers a reference software stack for in-vehicle use.
+
+ACRN Supported Use Cases
+************************
+
+Software Defined Cockpit
+========================
+
+The SDC system consists of multiple systems: the instrument cluster (IC)
+system, the In-vehicle Infotainment (IVI) system, and one or more rear
+seat entertainment (RSE) systems.  Each system is run as a VM for better
+isolation.
+
+The Instrument Control (IC) system manages graphics display of
+
+- driving speed, engine RPM, temperature, fuel level, odometer, trip mile, etc.
+- alerts of low fuel or tire pressure
+- rear-view camera(RVC) and surround-camera view for driving assistance.
+
+In-Vehicle Infotainment
+=======================
+
+A typical In-Vehicle Infotainment (IVI) system would support:
+
+- Navigation systems;
+- Radios, audio and video playback;
+- Mobile devices connection for  calls, music and applications via voice
+  recognition and/or gesture Recognition / Touch.
+- Rear-seat RSE services of entertainment system;
+- virtual office;
+- Connection to IVI front system and mobile devices (cloud
+  connectivity).
+
+ACRN supports guest OSes of Clear Linux and Android. OEMs can use the ACRN
+hypervisor and Linux or Android guest OS reference code to implement their own
+VMs for a customized IC/IVI/RSE.
+
+Hardware Requirements
+*********************
+
+Mandatory IA CPU features are support for:
+
+- Long mode
+- MTRR
+- TSC deadline timer
+- NX, SMAP, SMEP
+- Intel-VT including VMX, EPT, VT-d, APICv, VPID, invept and invvpid
+
+Recommended Memory: 4GB, with 8GB preferred.

doc/developer-guides/hld/index.rst

@@ -14,7 +14,7 @@ background, and motivation for specific areas within the ACRN hypervisor
 system.
 
 .. toctree::
-   :maxdepth: 1
+   :maxdepth: 2
 
    Overview <hld-overview>
    Hypervisor <hld-hypervisor>