UVC系列4-定制Android kernel UVC部分支持相对和绝对参数

本文主要是介绍UVC系列4-定制Android kernel UVC部分支持相对和绝对参数，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1、添加参数

在熟悉了android uvc控制参数和UVC协议之后，现在可以着手定制android UVC协议了，添加相对控制参数。

1.1 添加相对控制pan和tilt

第一步，添加相对控制pan和tilt修改的文件是：drivers\media\usb\uvc\uvc_ctrl.c
在uvc_control_info uvc_ctrls[]结构体中添加：

{.entity     = UVC_GUID_UVC_CAMERA,.selector  	= UVC_CT_PANTILT_RELATIVE_CONTROL,.index      = 12,.size       = 4,.flags     	= UVC_CTRL_FLAG_SET_CUR|UVC_CTRL_FLAG_GET_RANGE|UVC_CTRL_FLAG_AUTO_UPDATE,
}

在结构体uvc_control_mapping uvc_ctrl_mappings[]中添加：

{.id = V4L2_CID_PAN_RELATIVE,.name = "Pan (Relative)",.entity = UVC_GUID_UVC_CAMERA,.selector = UVC_CT_PANTILT_RELATIVE_CONTROL,.size = 16,.offset = 0,.v4l2_type = V4L2_CTRL_TYPE_INTEGER,.data_type = UVC_CTRL_DATA_TYPE_SIGNED,.get = uvc_ctrl_get_rel_speed,.set = uvc_ctrl_set_rel_speed,
},
{.id = V4L2_CID_TILT_RELATIVE,.name= "Tilt (Relative)",.entity= UVC_GUID_UVC_CAMERA,.selector= UVC_CT_PANTILT_RELATIVE_CONTROL,.size= 16,.offset= 16,.v4l2_type= V4L2_CTRL_TYPE_INTEGER,.data_type= UVC_CTRL_DATA_TYPE_SIGNED,.get= uvc_ctrl_get_rel_speed,.set= uvc_ctrl_set_rel_speed,
}

1.2 添加pan和tilt的速度控制

其中uvc_ctrl_get_rel_speed和uvc_ctrl_set_rel_speed映射到的方法对应UVC协议里面的速度控制，在uvc_ctrl.c文件中也要添加这两个方法的实现，与zoom对应的控制方法类似，具体实现方法是：

static __s32 uvc_ctrl_get_rel_speed(structuvc_control_mapping *mapping,__u8query, const __u8 *data)
{intfirst = mapping->offset / 8;__s8rel = (__s8)data[first];switch (query) {case UVC_GET_CUR:return (rel == 0) ? 0 : (rel > 0 ?data[first+1]:-data[first+1]);case UVC_GET_MIN:return -data[first+1];case UVC_GET_MAX:case UVC_GET_RES:case UVC_GET_DEF:default:return data[first+1];
}
}
static void uvc_ctrl_set_rel_speed(structuvc_control_mapping *mapping,__s32 value, __u8 *data)
{intfirst = mapping->offset / 8;data[first] = value == 0 ? 0 : (value > 0)? 1 : 0xff;data[first+1] = min_t(int, abs(value), 0xff);
}

可以看到这里的赋值也是与UVC协议对应的。另外针对绝对控制，目前在结构体uvc_control_mappinguvc_ctrl_mappings[]中的定义是：

{.id             = V4L2_CID_PAN_ABSOLUTE,.name               = "Pan (Absolute)",.entity               = UVC_GUID_UVC_CAMERA,.selector  = UVC_CT_PANTILT_ABSOLUTE_CONTROL,.size          = 32,.offset              = 0,.v4l2_type        = V4L2_CTRL_TYPE_INTEGER,.data_type       = UVC_CTRL_DATA_TYPE_UNSIGNED,
},
{.id             = V4L2_CID_TILT_ABSOLUTE,.name               = "Tilt (Absolute)",.entity               = UVC_GUID_UVC_CAMERA,.selector  = UVC_CT_PANTILT_ABSOLUTE_CONTROL,.size          = 32,.offset              = 32,.v4l2_type        = V4L2_CTRL_TYPE_INTEGER,.data_type       = UVC_CTRL_DATA_TYPE_UNSIGNED,
}

可以看看这两个控制参数的data_type是UVC_CTRL_DATA_TYPE_UNSIGNED，而UVC协议里面定义的是：

1.3 修改参数类型

Value的类型是signed number，此时我们需要将UNSIGNED改为signed，将这个data_type统一改成signed，即UVC_CTRL_DATA_TYPE_SIGNED。
下一步uvc_control_mapping uvc_ctrl_mappings[]中添加速度控制的参数，如下：

{.id             = V4L2_CID_PAN_SPEED,.name               = "Pan (Speed)",.entity               = UVC_GUID_UVC_CAMERA,.selector  = UVC_CT_PANTILT_RELATIVE_CONTROL,.size          = 16,.offset              = 0,.v4l2_type        = V4L2_CTRL_TYPE_INTEGER,.data_type       = UVC_CTRL_DATA_TYPE_SIGNED,.get          = uvc_ctrl_get_rel_speed,.set           = uvc_ctrl_set_rel_speed,
},
{.id             = V4L2_CID_TILT_SPEED,.name               = "Tilt (Speed)",.entity               = UVC_GUID_UVC_CAMERA,.selector  = UVC_CT_PANTILT_RELATIVE_CONTROL,.size          =16,.offset              = 16,.v4l2_type        = V4L2_CTRL_TYPE_INTEGER,.data_type       = UVC_CTRL_DATA_TYPE_SIGNED,.get          = uvc_ctrl_get_rel_speed,.set           = uvc_ctrl_set_rel_speed,
}

针对相对控制的两个参数id V4L2_CID_PAN_RELATIVE和V4L2_CID_PAN_RELATIVE，两个控制速度的参数V4L2_CID_PAN_SPEED和V4L2_CID_TILT_SPEED需要定义，修改两个文件，第一个文件位置位于drivers\media\v4l2-core\v4l2-ctrls.c文件中，const char *v4l2_ctrl_get_name中添加：

caseV4L2_CID_PAN_RELATIVE:      return"Pan, Relative";
caseV4L2_CID_TILT_RELATIVE:     return"Tilt, Relative";
caseV4L2_CID_PAN_SPEED:         return"Pan, Speed";
caseV4L2_CID_TILT_SPEED:        return"Tilt, Speed";

第二个文件位于include/uapi/linux/v4l2-controls.h，添加定义：

#define V4L2_CID_PAN_RELATIVE                   (V4L2_CID_CAMERA_CLASS_BASE+4)
#define V4L2_CID_TILT_RELATIVE                  (V4L2_CID_CAMERA_CLASS_BASE+5)
#define V4L2_CID_PAN_SPEED                      (V4L2_CID_CAMERA_CLASS_BASE+32)
#define V4L2_CID_TILT_SPEED                     (V4L2_CID_CAMERA_CLASS_BASE+33)