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+Virtual System Controller
+=========================
+
+This device is a simple interface defined for the pure virtual machine with no
+hardware reference implementation to allow the guest kernel to send command
+to the host hypervisor.
+
+The specification can evolve, the current state is defined as below.
+
+This is a MMIO mapped device using 256 bytes.
+
+Two 32bit registers are defined:
+
+1- the features register (read-only, address 0x00)
+
+ This register allows the device to report features supported by the
+ controller.
+ The only feature supported for the moment is power control (0x01).
+
+2- the command register (write-only, address 0x04)
+
+ This register allows the kernel to send the commands to the hypervisor.
+ The implemented commands are part of the power control feature and
+ are reset (1), halt (2) and panic (3).
+ A basic command, no-op (0), is always present and can be used to test the
+ register access. This command has no effect.