* persistence that is intended to be used when the device is being treated as a
* head mounted display (HMD). The actual display brightness in this mode is
* implementation dependent, and any value set for color in light_state may be
- * overriden by the HAL implementation.
+ * overridden by the HAL implementation.
*
- * For an optimal HMD viewing experience, the display should meet the following
+ * For an optimal HMD viewing experience, the display must meet the following
* criteria in this mode:
- * - Less than 2ms display persistence.
+ * - Gray-to-Gray, White-to-Black, and Black-to-White switching time must be ≤ 3 ms.
+ * - The display must support low-persistence with ≤ 3.5 ms persistence.
+ * Persistence is defined as the amount of time for which a pixel is
+ * emitting light for a single frame.
* - Any "smart panel" or other frame buffering options that increase display
* latency are disabled.
* - Display brightness is set so that the display is still visible to the user
* under normal indoor lighting.
+ * - The display must update at 60 Hz at least, but higher refresh rates are
+ * recommended for low latency.
*
* This mode will only be used with light devices of type LIGHT_ID_BACKLIGHT,
* and will only be called by the Android framework for light_device_t
* and gyro to an application-visible callback must be extremely low (<5ms
* typically). This is required for HIFI sensor support.
* - Low display latency - Total end-to-end latency from the GPU draw calls to
- * the actual display update must be as low as possible. This is typically
- * achieved by using SurfaceFlinger in a single-buffered mode, and assuring
- * that draw calls are synchronized with the display scanout correctly. Any
- * GPU settings required to allow consistent performance of this operation
- * are required, including the EGL extensions: EGL_IMG_context_priority, and
- * EGL_XXX_set_render_buffer_mode.
+ * the actual display update must be as low as possible. This is achieved by
+ * using SurfaceFlinger in a single-buffered mode, and assuring that draw calls
+ * are synchronized with the display scanout correctly. This behavior is
+ * exposed via an EGL extension to applications. See below for the EGL
+ * extensions needed for this.
* - Low-persistence display - Display persistence settings must be set as low as
* possible while still maintaining a reasonable brightness. For a typical
- * display running at 60Hz, pixels should be illuminated for <4ms to be
- * considered low-persistence (<2ms is desirable). This avoids ghosting
- * during movements in a VR setting.
+ * display running at 60Hz, pixels should be illuminated for <=3.5ms to be
+ * considered low-persistence. This avoids ghosting during movements in a VR
+ * setting, and should be enabled from the lights.h HAL when
+ * BRIGHTNESS_MODE_LOW_PERSISTENCE is set.
* - Consistent performance of the GPU and CPU - When given a mixed GPU/CPU
* workload for a VR application with bursts of work at regular intervals
- * several times a frame. CPU scheduling should ensure that the application
- * render thread is run consistently within 1ms of when required for the
- * draw window, and an appropriate clockrate is maintained to ensure the
- * workload finishes within the time alloted to the draw window. Likewise,
- * GPU scheduling should ensure that work from the application render thread
- * is given priority over other GPU work, and that a high enough clockrate can
- * be maintained to ensure that this completes within the draw window. CTS
- * tests with example VR workloads will be available to assess performance
- * tuning.
+ * several times a frame, the CPU scheduling should ensure that the application
+ * render thread work is run consistently within 1ms of when scheduled, and
+ * completed before the end of the draw window. To this end, a single CPU core
+ * must be reserved for solely for the currently running VR application's render
+ * thread while in VR mode, and made available in the "top-app" cpuset.
+ * Likewise, an appropriate CPU, GPU, and bus clockrate must be maintained to
+ * ensure that the rendering workload finishes within the time allotted to
+ * render each frame when the POWER_HINT_SUSTAINED_PERFORMANCE flag has been
+ * set in the power.h HAL while in VR mode when the device is not being
+ * thermally throttled.
+ * - Required EGL extensions must be present - Any GPU settings required to allow
+ * the above capabilities are required, including the EGL extensions:
+ * EGL_ANDROID_create_native_client_buffer, EGL_ANDROID_front_buffer_auto_refresh,
+ * EGL_EXT_protected_content, EGL_KHR_mutable_render_buffer,
+ * EGL_KHR_reusable_sync, and EGL_KHR_wait_sync.
+ * - Accurate thermal reporting - Accurate thermal temperatures and limits must be
+ * reported in the thermal.h HAL. Specifically, the current skin temperature
+ * must accurately be reported for DEVICE_TEMPERATURE_SKIN and the
+ * vr_throttling_threshold reported for this device must accurately report the
+ * temperature limit above which the device's thermal governor throttles the
+ * CPU, GPU, and/or bus clockrates below the minimum necessary for consistent
+ * performance (see previous bullet point).
*
- * Vendors implementing this HAL are expected to use set_vr_mode as a hint to
- * enable VR-specific performance tuning, and to turn on any device features
- * optimal for VR display modes (or do nothing if none are available). Devices
- * that advertise FEATURE_VR_MODE_HIGH_PERFORMANCE are must pass the additional
- * CTS performance tests required for this feature and follow the additional
- * guidelines for hardware implementation for "VR Ready" devices.
+ * In general, vendors implementing this HAL are expected to use set_vr_mode as a
+ * hint to enable VR-specific performance tuning needed for any of the above
+ * requirements, and to turn on any device features optimal for VR display
+ * modes. The set_vr_mode call may simply do nothing if no optimizations are
+ * available or necessary to meet the above requirements.
*
* No methods in this HAL will be called concurrently from the Android framework.
*/
typedef struct vr_module {
/**
* Common methods of the module. This *must* be the first member of
- * vr_module as users of * this structure will cast a hw_module_t to a
+ * vr_module as users of this structure may cast a hw_module_t to a
* vr_module pointer in contexts where it's known that the hw_module_t
* references a vr_module.
*/
* false - VR mode is disabled, turn off all VR-specific settings.
* true - VR mode is enabled, turn on all VR-specific settings.
*
- * This is called from the VrManagerService whenever the application(s)
- * currently in use enters or leaves VR mode. This will typically occur
- * when the user switches or from an application that has indicated to
- * system_server that it should run in VR mode.
+ * This is called whenever the the Android system enters or leaves VR mode.
+ * This will typically occur when the user switches to or from a VR application
+ * that is doing stereoscopic rendering.
*/
void (*set_vr_mode)(struct vr_module *module, bool enabled);
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