在移植sensor的hal层代码时, SensorBase.cpp作为所有sensor类的基类, 定义了一些很有用的方法.
下面jwisp结合实际实验, 来跟大家分析下SensorBase的作用和流程
SensorBase::SensorBase( const char* dev_name, const char* data_name) : dev_name(dev_name), data_name(data_name), dev_fd(-1), data_fd(-1) { data_fd = openInput(data_name); }
SensorBase的构造, 子类会先调用父类的这个方法,
在SensorBase构造中, 将子类传来的设备名称dev_name和数据设备名data_name赋值本类成员,
然后通过openInput函数,打开data_name然后将open后的句柄, 传递给data_fd
SensorBase::~SensorBase() { if (data_fd >= 0) { close(data_fd); } if (dev_fd >= 0) { close(dev_fd); } }
析构函数, 关闭data_fd和dev_fd
int SensorBase::open_device() { if (dev_fd<0 && dev_name) { dev_fd = open(dev_name, O_RDONLY); LOGE_IF(dev_fd<0, "Couldn't open %s (%s)", dev_name, strerror(errno)); } return 0; } int SensorBase::close_device() { if (dev_fd >= 0) { close(dev_fd); dev_fd = -1; } return 0; }
通过设备句柄, 打开和关闭设备
int SensorBase::getFd() const { return data_fd; } int SensorBase::setDelay(int32_t handle, int64_t ns) { return 0; } bool SensorBase::hasPendingEvents() const { return false; } int64_t SensorBase::getTimestamp() { struct timespec t; t.tv_sec = t.tv_nsec = 0; clock_gettime(CLOCK_MONOTONIC, &t); return int64_t(t.tv_sec)*1000000000LL + t.tv_nsec; }
这四个函数, 基本上是由子类覆写的.
getFd()得到data_fd句柄
setDelay()设置上报延迟频率
hasPendingEvents()是否还有未上报的事件
getTimestamp()获得时间戳
接下来就是本类最重要的openInput()方法了
int SensorBase::openInput(const char* inputName) { int fd = -1; const char *dirname = "/dev/input"; char devname[PATH_MAX]; char *filename; DIR *dir; struct dirent *de; dir = opendir(dirname); if(dir == NULL) return -1; strcpy(devname, dirname); filename = devname + strlen(devname); *filename++ = '/'; while((de = readdir(dir))) { if(de->d_name[0] == '.' && (de->d_name[1] == '\0' || (de->d_name[1] == '.' && de->d_name[2] == '\0'))) continue; strcpy(filename, de->d_name); fd = open(devname, O_RDONLY); if (fd>=0) { char name[80]; if (ioctl(fd, EVIOCGNAME(sizeof(name) - 1), &name) < 1) { name[0] = '\0'; } if (!strcmp(name, inputName)) { break; } else { close(fd); fd = -1; } } } closedir(dir); LOGE_IF(fd<0, "couldn't find '%s' input device", inputName); return fd; }
此方法最终返回的是, 传入的inputName相对应的字符设备的句柄
首先打开的是dirname (jwisp这里是/dev/input/)
打开后,轮询所有的字符节点, 从轮询到的字符节点获取name, 若name与传递来的子类inputName相同则将打开这个设备的句柄返回.
若不相同则关闭其他设备.