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| author | Gina Dimino <gdimino@google.com> | 2021-07-15 23:27:11 +0000 |
|---|---|---|
| committer | Gerrit Code Review <noreply-gerritcodereview@google.com> | 2021-07-15 23:27:11 +0000 |
| commit | 72e0ae8d8207042452f75874221103f4f6b3014a (patch) | |
| tree | 7fa97b880b85be7de5b713d233cdc407c20b88cd /en/devices/architecture/hal.html | |
| parent | e55b3193405187e091a4ac7730ef04360ec04504 (diff) | |
| parent | fc5fc0e74df003b0ee454d3418b88cd722282c49 (diff) | |
| download | source.android.com-master.tar.gz | |
Diffstat (limited to 'en/devices/architecture/hal.html')
| -rw-r--r-- | en/devices/architecture/hal.html | 138 |
1 files changed, 0 insertions, 138 deletions
diff --git a/en/devices/architecture/hal.html b/en/devices/architecture/hal.html deleted file mode 100644 index 12525a65..00000000 --- a/en/devices/architecture/hal.html +++ /dev/null @@ -1,138 +0,0 @@ -<html devsite> - <head> - <title>Legacy HALs</title> - <meta name="project_path" value="/_project.yaml" /> - <meta name="book_path" value="/_book.yaml" /> - </head> - <body> - <!-- - Copyright 2017 The Android Open Source Project - - Licensed under the Apache License, Version 2.0 (the "License"); - you may not use this file except in compliance with the License. - You may obtain a copy of the License at - - http://www.apache.org/licenses/LICENSE-2.0 - - Unless required by applicable law or agreed to in writing, software - distributed under the License is distributed on an "AS IS" BASIS, - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - See the License for the specific language governing permissions and - limitations under the License. - --> - - - -<p>A HAL defines a standard interface for hardware vendors to implement, -which enables Android to be agnostic about lower-level driver implementations. -Using a HAL allows you to implement functionality without affecting or modifying -the higher level system. This page describes the older architecture, which is no -longer supported as of Android 8.0. For Android 8.0 and higher, please see -<a href="/devices/architecture/hal-types/">HAL Types</a>.</p> - -<img src="../images/ape_fwk_hal.png"> - -<p class="img-caption"><strong>Figure 1.</strong> HAL components</p> - -<p>You must implement the corresponding HAL (and driver) for the specific -hardware your product provides. HAL implementations are typically built into -shared library modules (<code>.so</code> files), but as Android does not mandate -a standard interaction between a HAL implementation and device drivers, you can -do what is best for your situation. However, to enable the Android system to -correctly interact with your hardware, you <strong>must</strong> abide by the -contract defined in each hardware-specific HAL interface.</p> - -<p>To guarantee that HALs have a predictable structure, each hardware-specific -HAL interface has properties defined in -<code>hardware/libhardware/include/hardware/hardware.h</code>. This interface -allows the Android system to load correct versions of your HAL modules in a -consistent way. A HAL interface consists of two components: modules and devices. -</p> - -<h2 id="hal-module">HAL modules</h2> -<p>A module represents your packaged HAL implementation, which is stored as a -shared library (<code>.so file</code>). The -<code>hardware/libhardware/include/hardware/hardware.h</code> header file -defines a struct (<code>hw_module_t</code>) that represents a module and -contains metadata such as the version, name, and author of the module. Android -uses this metadata to find and load the HAL module correctly.</p> - -<p>In addition, the <code>hw_module_t</code> struct contains a pointer to -another struct, <code>hw_module_methods_t</code>, that contains a pointer to -an open function for the module. This open function is used to initiate -communication with the hardware for which the HAL is serving as an abstraction. -Each hardware-specific HAL usually extends the generic <code>hw_module_t</code> -struct with additional information for that specific piece of hardware. For -example, in the camera HAL, the <code>camera_module_t</code> struct contains a -<code>hw_module_t</code> struct along with other camera-specific function -pointers:</p> - -<pre class="devsite-click-to-copy"> -typedef struct camera_module { - hw_module_t common; - int (*get_number_of_cameras)(void); - int (*get_camera_info)(int camera_id, struct camera_info *info); -} camera_module_t; -</pre> - -<p>When you implement a HAL and create the module struct, you must name it -<code>HAL_MODULE_INFO_SYM</code>. Example from the Nexus 9 audio HAL:</p> - -<pre class="devsite-click-to-copy"> -struct audio_module HAL_MODULE_INFO_SYM = { - .common = { - .tag = HARDWARE_MODULE_TAG, - .module_api_version = AUDIO_MODULE_API_VERSION_0_1, - .hal_api_version = HARDWARE_HAL_API_VERSION, - .id = AUDIO_HARDWARE_MODULE_ID, - .name = "NVIDIA Tegra Audio HAL", - .author = "The Android Open Source Project", - .methods = &hal_module_methods, - }, -}; -</pre> - -<h2 id="hal-device">HAL devices</h2> -<p>A device abstracts the hardware of your product. For example, an audio -module can contain a primary audio device, a USB audio device, or a Bluetooth -A2DP audio device.</p> - -<p>A device is represented by the <code>hw_device_t</code> struct. Similar to a -module, each type of device defines a detailed version of the generic -<code>hw_device_t</code> that contains function pointers for specific features -of the hardware. For example, the <code>audio_hw_device_t</code> struct type -contains function pointers to audio device operations:</p> - -<pre class="devsite-click-to-copy"> -struct audio_hw_device { - struct hw_device_t common; - - /** - * used by audio flinger to enumerate what devices are supported by - * each audio_hw_device implementation. - * - * Return value is a bitmask of 1 or more values of audio_devices_t - */ - uint32_t (*get_supported_devices)(const struct audio_hw_device *dev); - ... -}; -typedef struct audio_hw_device audio_hw_device_t; -</pre> - -<p>In addition to these standard properties, each hardware-specific HAL -interface can define more of its own features and requirements. For details, -see the <a href="/reference/hal/">HAL reference documentation</a> as well as -the individual instructions for each HAL.</p> - -<h2 id="hal-building">Building HAL modules</h2> -<p>HAL implementations are built into modules (<code>.so</code>) files and are -dynamically linked by Android when appropriate. You can build your modules by -creating <code>Android.mk</code> files for each of your HAL implementations -and pointing to your source files. In general, your shared libraries must be -named in a specific format so they can be found and loaded properly. The naming -scheme varies slightly from module to module, but follows the general pattern -of: <code><module_type>.<device_name></code>. -</p> - - </body> -</html> |