1Virtual System Controller 2========================= 3 4The ``virt-ctrl`` device is a simple interface defined for the pure 5virtual machine with no hardware reference implementation to allow the 6guest kernel to send command to the host hypervisor. 7 8The specification can evolve, the current state is defined as below. 9 10This is a MMIO mapped device using 256 bytes. 11 12Two 32bit registers are defined: 13 14the features register (read-only, address 0x00) 15 This register allows the device to report features supported by the 16 controller. 17 The only feature supported for the moment is power control (0x01). 18 19the command register (write-only, address 0x04) 20 This register allows the kernel to send the commands to the hypervisor. 21 The implemented commands are part of the power control feature and 22 are reset (1), halt (2) and panic (3). 23 A basic command, no-op (0), is always present and can be used to test the 24 register access. This command has no effect. 25