[mirror_qemu.git] / docs / specs / virt-ctlr.rst

Virtual System Controller
=========================

The ``virt-ctrl`` 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:

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).

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.
Commit	Line	Data
0791bc02 LV	1	Virtual System Controller
	2	=========================
	3
6e0c8492 PM	4	The ``virt-ctrl`` device is a simple interface defined for the pure
	5	virtual machine with no hardware reference implementation to allow the
	6	guest kernel to send command to the host hypervisor.
0791bc02 LV	7
	8	The specification can evolve, the current state is defined as below.
	9
	10	This is a MMIO mapped device using 256 bytes.
	11
	12	Two 32bit registers are defined:
	13
6e0c8492	14	the features register (read-only, address 0x00)
0791bc02 LV	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
6e0c8492	19	the command register (write-only, address 0x04)
0791bc02 LV	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.