2 * Copyright (C) 2016 The Android Open Source Project
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef ANDROID_INCLUDE_HARDWARE_VR_H
18 #define ANDROID_INCLUDE_HARDWARE_VR_H
21 #include <sys/cdefs.h>
22 #include <hardware/hardware.h>
26 #define VR_HARDWARE_MODULE_ID "vr"
28 #define VR_MODULE_API_VERSION_1_0 HARDWARE_MODULE_API_VERSION(1, 0)
31 * Implement this HAL to receive callbacks when a virtual reality (VR)
32 * application is being used. VR applications characteristically have a number
33 * of special display and performance requirements, including:
34 * - Low sensor latency - Total end-to-end latency from the IMU, accelerometer,
35 * and gyro to an application-visible callback must be extremely low (<5ms
36 * typically). This is required for HIFI sensor support.
37 * - Low display latency - Total end-to-end latency from the GPU draw calls to
38 * the actual display update must be as low as possible. This is typically
39 * achieved by using SurfaceFlinger in a single-buffered mode, and assuring
40 * that draw calls are synchronized with the display scanout correctly. Any
41 * GPU settings required to allow consistent performance of this operation
42 * are required, including the EGL extensions: EGL_IMG_context_priority, and
43 * EGL_XXX_set_render_buffer_mode.
44 * - Low-persistence display - Display persistence settings must be set as low as
45 * possible while still maintaining a reasonable brightness. For a typical
46 * display running at 60Hz, pixels should be illuminated for <4ms to be
47 * considered low-persistence (<2ms is desirable). This avoids ghosting
48 * during movements in a VR setting.
49 * - Consistent performance of the GPU and CPU - When given a mixed GPU/CPU
50 * workload for a VR application with bursts of work at regular intervals
51 * several times a frame. CPU scheduling should ensure that the application
52 * render thread is run consistently within 1ms of when required for the
53 * draw window, and an appropriate clockrate is maintained to ensure the
54 * workload finishes within the time alloted to the draw window. Likewise,
55 * GPU scheduling should ensure that work from the application render thread
56 * is given priority over other GPU work, and that a high enough clockrate can
57 * be maintained to ensure that this completes within the draw window. CTS
58 * tests with example VR workloads will be available to assess performance
61 * Vendors implementing this HAL are expected to use set_vr_mode as a hint to
62 * enable VR-specific performance tuning, and to turn on any device features
63 * optimal for VR display modes (or do nothing if none are available). Devices
64 * that advertise FEATURE_VR_MODE_HIGH_PERFORMANCE are must pass the additional
65 * CTS performance tests required for this feature and follow the additional
66 * guidelines for hardware implementation for "VR Ready" devices.
68 * No methods in this HAL will be called concurrently from the Android framework.
70 typedef struct vr_module {
72 * Common methods of the module. This *must* be the first member of
73 * vr_module as users of * this structure will cast a hw_module_t to a
74 * vr_module pointer in contexts where it's known that the hw_module_t
75 * references a vr_module.
77 struct hw_module_t common;
80 * Convenience method for the HAL implementation to set up any state needed
81 * at runtime startup. This is called once from the VrManagerService during
82 * its boot phase. No methods from this HAL will be called before init.
84 void (*init)(struct vr_module *module);
87 * Set the VR mode state. Possible states of the enabled parameter are:
88 * false - VR mode is disabled, turn off all VR-specific settings.
89 * true - VR mode is enabled, turn on all VR-specific settings.
91 * This is called from the VrManagerService whenever the application(s)
92 * currently in use enters or leaves VR mode. This will typically occur
93 * when the user switches or from an application that has indicated to
94 * system_server that it should run in VR mode.
96 void (*set_vr_mode)(struct vr_module *module, bool enabled);
98 /* Reserved for future use. Must be NULL. */
99 void* reserved[8 - 2];
104 #endif /* ANDROID_INCLUDE_HARDWARE_VR_H */