camera_trigger摸索
PX4学习二：camera_trigger的参数问题
PX4新增的相机触发位于Firmware\src\drivers\camera_trigger，它的目录结构如下1
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12|- camera_trigger
|- interfaces 接口程序
|- src
|- camera_interface.cpp
|- camera_interface.h 相机API
|- pwm.cpp
|- pwm.h 继承API类，用于SeagullMAP2实现
|- relay.cpp
|- relay.h 继承API类，用于GPIO实现
|- camera_trigger.cpp 相机触发主程序
|- camera_trigger_params.c 相关参数
|- CMakeLists.txt
其中，在camera_interface包含了一个相机接口的类，而pwm和relay则是通过继承这个类实现的。具体实现尚未研究，这次仅仅是研究了camera_trigger_params.c中的参数设置。
以下是camera_trigger_params.c中的参数1
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95/**
* Camera trigger Interface
*
* Selects the trigger interface
* 选择使用的触发接口
* @value 1 GPIO
* @value 2 Seagull MAP2 (PWM)
*
* @reboot_required true
*
* @group Camera trigger
*/
PARAM_DEFINE_INT32(TRIG_INTERFACE, 2);
/**
* Camera trigger interval
*
* This parameter sets the time between two consecutive trigger events
* 用于时间间隔模式下的时间设置
* @unit ms
* @min 4.0
* @max 10000.0
* @decimal 1
* @group Camera trigger
*/
PARAM_DEFINE_FLOAT(TRIG_INTERVAL, 40.0f);
/**
* Camera trigger polarity
*
* This parameter sets the polarity of the trigger (0 = active low, 1 = active high )
* 选择高电平触发还是低电平触发
* @value 0 Active low
* @value 1 Active high
* @min 0
* @max 1
* @group Camera trigger
*/
PARAM_DEFINE_INT32(TRIG_POLARITY, 1);
/**
* Camera trigger activation time
*
* This parameter sets the time the trigger needs to pulled high or low.
* 触发时间
* @unit ms
* @min 0.1
* @max 3000
* @decimal 1
* @group Camera trigger
*/
PARAM_DEFINE_FLOAT(TRIG_ACT_TIME, 0.5f);
/**
* Camera trigger mode
* 触发模式
* @value 0 Disable
* @value 1 On individual commands
* @value 2 Time based, always on
* @value 3 Distance based, always on
* @value 4 Distance, mission controlled
* @min 0
* @max 4
* @reboot_required true
* @group Camera trigger
*/
PARAM_DEFINE_INT32(TRIG_MODE, 0);
/**
* Camera trigger pin
* 选择触发的pin口
* Selects which pin is used, ranges from 1 to 6 (AUX1-AUX6 on px4fmu-v2 and the rail
* pins on px4fmu-v4). The PWM interface takes two pins per camera, while relay
* triggers on every pin individually. Example: Value 34 would trigger on pins 3 and 4.
*
* @min 1
* @max 123456
* @decimal 0
* @reboot_required true
* @group Camera trigger
*/
PARAM_DEFINE_INT32(TRIG_PINS, 6);
/**
* Camera trigger distance
*
* Sets the distance at which to trigger the camera.
* 距离间隔触发模式下用于设置距离
* @unit m
* @min 0
* @increment 1
* @decimal 1
* @group Camera trigger
*/
PARAM_DEFINE_FLOAT(TRIG_DISTANCE, 25.0f);
通过修改这个文件里的参数，便可以达到各种目的。
接着就是camera_trigger.cpp中几个重要参数的使用1
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44/*
首先定义了接口模式这个枚举变量，用于判断使用哪种接口
*/
typedef enum {
CAMERA_INTERFACE_MODE_NONE = 0,
CAMERA_INTERFACE_MODE_RELAY,
CAMERA_INTERFACE_MODE_SEAGULL_MAP2_PWM
} camera_interface_mode_t;
...
// 这里创建了接口模式和一个接口对象，接口对象在构造函数中赋值为nullptr
camera_interface_mode_t _camera_interface_mode;
CameraInterface *_camera_interface; ///< instance of camera interface
...
// Parameters
// PX4最常使用的参数设置方法，先通过param_find(), 再通过param_get()指向变量
_p_interval = param_find("TRIG_INTERVAL");
_p_distance = param_find("TRIG_DISTANCE");
_p_activation_time = param_find("TRIG_ACT_TIME");
_p_mode = param_find("TRIG_MODE");
_p_interface = param_find("TRIG_INTERFACE");
param_get(_p_activation_time, &_activation_time);
param_get(_p_interval, &_interval);
param_get(_p_distance, &_distance);
param_get(_p_mode, &_mode);
param_get(_p_interface, &_camera_interface_mode);
// 判断接口的模式来建立不同子类对象，因此可用通过在interfaces\src中建立新方法来实现不同接口模式，仅需要修改这里
switch (_camera_interface_mode) {
case CAMERA_INTERFACE_MODE_RELAY:
_camera_interface = new CameraInterfaceRelay;
break;
case CAMERA_INTERFACE_MODE_SEAGULL_MAP2_PWM:
_camera_interface = new CameraInterfacePWM;
break;
default:
break;
}
