鑑於上一篇介紹完 framework 層 sensor 相關的服務初始和啟動，
這一篇我們來看看 8.0 版本之後的 HAL 架構，
因為 HIDL 已經在先前系列文章探討過了所以就不贅述。
檔案內容在 hardware 底下大概長這樣：
interfaces/sensors/
└── 1.0
├── Android.bp
├── default
│ ├── Android.bp
│ ├── android.hardware.sensors@1.0-service.rc
│ ├── convert.cpp
│ ├── include
│ │ └── sensors
│ │ └── convert.h
│ ├── OWNERS
│ ├── Sensors.cpp
│ ├── Sensors.h
│ └── service.cpp
├── ISensors.hal
├── types.hal
└── vts
└── functional
├── Android.bp
├── GrallocWrapper.cpp
├── GrallocWrapper.h
├── OWNERS
└── VtsHalSensorsV1_0TargetTest.cpp
可以看到跟舊版不同的地方式，
有新增一個 service 控制 HAL，
和 framework 的 SensorService (的SensorDevice) 之間通信，
假如你在 adb shell 環境下可以透過 ps 指令查詢得到。
上面編譯成可執行程序放在 /vendor/bin/hw/ 裡。
主要的類由 Sensors 類繼承，
並實現了android::hardware::sensors::V1_0::ISensors
裡面聲明的那些 SensorService 可以通過 HIDL 調用的方法，
如 activate()、poll()、flush( )、getSensorsLis() 等。
來看一下架構：
hardware/interfaces/sensors/1.0/default/Sensors.cpp
56 Sensors::Sensors()
57 : mInitCheck(NO_INIT),
58 mSensorModule(nullptr),
59 mSensorDevice(nullptr) {
60 status_t err = OK;
61 if (UseMultiHal()) {
**//走這邊，獲取vendor-hal的module的方法**
62 mSensorModule = ::get_multi_hal_module_info();
63 } else {
64 err = **hw_get_module**(
65 SENSORS_HARDWARE_MODULE_ID,
66 (hw_module_t const **)&mSensorModule);
67 }
68 if (mSensorModule == NULL) {
69 err = UNKNOWN_ERROR;
70 }
71
72 if (err != OK) {
73 LOG(ERROR) << "Couldn't load "
74 << SENSORS_HARDWARE_MODULE_ID
75 << " module ("
76 << strerror(-err)
77 << ")";
78
79 mInitCheck = err;
80 return;
81 }
82
**//這邊是調用了multihal.cpp的open_sensors()方法，對mSensorDevice進行初始化**
83 err = **sensors_open_1(&mSensorModule->common, &mSensorDevice);**
84
85 if (err != OK) {
86 LOG(ERROR) << "Couldn't open device for module "
87 << SENSORS_HARDWARE_MODULE_ID
88 << " ("
89 << strerror(-err)
90 << ")";
91
92 mInitCheck = err;
93 return;
94 }
這裡看到一些 hw_get_module 和 hw_module_t 就覺得親近很多，
至少你可以發現它只是包了一層 HIDL 服務來實現溝通，
但是基本的 HAL 宣告和實作還是按照以往舊版方式。
我們繼續來看一下 multihal.cpp 的 open_sensors() 方法是如何初始化 mSensorDevice：
hardware/libhardware/modules/sensors/multihal.cpp
787 static int open_sensors(const struct hw_module_t* hw_module, const char* name,
788 struct hw_device_t** hw_device_out) {
789 ALOGV("open_sensors begin...");
790
791 lazy_init_modules();
792
793 // Create proxy device, to return later.
794 sensors_poll_context_t *dev = new sensors_poll_context_t();
795 memset(dev, 0, sizeof(sensors_poll_device_1_t));
796 dev->proxy_device.common.tag = HARDWARE_DEVICE_TAG;
797 dev->proxy_device.common.version = SENSORS_DEVICE_API_VERSION_1_4;
798 dev->proxy_device.common.module = const_cast<hw_module_t*>(hw_module);
799 dev->proxy_device.common.close = device__close;
800 dev->proxy_device.activate = device__activate;
801 dev->proxy_device.setDelay = device__setDelay;
802 dev->proxy_device.poll = device__poll;
803 dev->proxy_device.batch = device__batch;
804 dev->proxy_device.flush = device__flush;
805 dev->proxy_device.inject_sensor_data = device__inject_sensor_data;
806 dev->proxy_device.register_direct_channel = device__register_direct_channel;
807 dev->proxy_device.config_direct_report = device__config_direct_report;
808
809 dev->nextReadIndex = 0;
810
811 // Open() the subhal modules. Remember their devices in a vector parallel to sub_hw_modules.
812 for (std::vector<hw_module_t*>::iterator it = sub_hw_modules->begin();
813 it != sub_hw_modules->end(); it++) {
814 sensors_module_t *sensors_module = (sensors_module_t*) *it;
815 struct hw_device_t* sub_hw_device;
816 int sub_open_result = sensors_module->common.methods->open(*it, name, &sub_hw_device);
817 if (!sub_open_result) {
818 if (!HAL_VERSION_IS_COMPLIANT(sub_hw_device->version)) {
819 ALOGE("SENSORS_DEVICE_API_VERSION_1_3 or newer is required for all sensor HALs");
820 ALOGE("This HAL reports non-compliant API level : %s",
821 apiNumToStr(sub_hw_device->version));
822 ALOGE("Sensors belonging to this HAL will get ignored !");
823 }
824 dev->addSubHwDevice(sub_hw_device);
825 }
826 }
827
828 // Prepare the output param and return
829 ***hw_device_out = &dev->proxy_device.common**;
830 ALOGV("...open_sensors end");
831 return 0;
832 }
這邊讓 mSensorDevice 指向 dev->proxy_device.common，
之後通過類型轉換，調用 mSensorDevice->xxx()，
就等於調用 dev->proxy_device.xxx()。
以 SensorService 調用 activate() 為例來分析一下：
hardware/interfaces/sensors/1.0/default/Sensors.cpp
151 Return<Result> Sensors::activate(
152 int32_t sensor_handle, bool enabled) {
153 return ResultFromStatus(
154 mSensorDevice->activate(
155 reinterpret_cast<sensors_poll_device_t *>(mSensorDevice),
156 sensor_handle,
157 enabled));
158 }
假如調用 mSensorDevice->activate()，
等於調用 dev->proxy_device.activate = device__activate ：
hardware/libhardware/modules/sensors/multihal.cpp
537 static int device__activate(struct sensors_poll_device_t *dev, int handle,
538 int enabled) {
539 sensors_poll_context_t* ctx = (sensors_poll_context_t*) dev;
540 return ctx->activate(handle, enabled);
541 }
再看 sensors_poll_context_t :: active：
hardware/libhardware/modules/sensors/multihal.cpp
310 int sensors_poll_context_t::activate(int handle, int enabled) {
311 int retval = -EINVAL;
312 ALOGV("activate");
313 int local_handle = get_local_handle(handle);
314 sensors_poll_device_t* v0 = this->get_v0_device_by_handle(handle);
315 if (halIsCompliant(this, handle) && local_handle >= 0 && v0) {
316 retval = v0->activate(v0, local_handle, enabled);
317 } else {
318 ALOGE("IGNORING activate(enable %d) call to non-API-compliant sensor handle=%d !",
319 enabled, handle);
320 }
321 ALOGV("retval %d", retval);
322 return retval;
323 }
下一篇我們就來稍微看看 hardware 底下 sensor 的其他文件吧！
https://blog.csdn.net/goodnight1994/article/details/80259222
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