文章选取android下linux-3.10作为分析对象,具体的UVC初始化过程可以参考csdn大神写的博客,地址是:http://blog.csdn.net/orz415678659。
uvc加载摄像头的过程无非是初始化设备,加载设备,获取设备相关参数并加载相关参数到buffer,此时就已经将视频和控制参数加载到buffer了,这篇文章主要关注的是控制相关的参数。
需要关注的两个核心文件是:
- drivers\media\usb\uvc\uvc_ctrl.c
- drivers\media\usb\uvc\uvc_v4l2.c
首先看看uvc_ctrl.c文件中的struct uvc_control_info uvc_ctrls[]
结构体,这个结构体中定义了摄像头的控制参数详情,主要包含了各种类型的控制,比如白平衡,曝光度等。其中需要重点关注的参数是上下左右和焦距的控制参数,如下:
{
.entity = UVC_GUID_UVC_CAMERA,
.selector = UVC_CT_ZOOM_ABSOLUTE_CONTROL,
.index = 9,
.size = 2,
.flags = UVC_CTRL_FLAG_SET_CUR
| UVC_CTRL_FLAG_GET_RANGE
| UVC_CTRL_FLAG_RESTORE
| UVC_CTRL_FLAG_AUTO_UPDATE,
},
{
.entity = UVC_GUID_UVC_CAMERA,
.selector = UVC_CT_ZOOM_RELATIVE_CONTROL,
.index = 10,
.size = 3,
.flags = UVC_CTRL_FLAG_SET_CUR
| UVC_CTRL_FLAG_GET_MIN
| UVC_CTRL_FLAG_GET_MAX
| UVC_CTRL_FLAG_GET_RES
| UVC_CTRL_FLAG_GET_DEF
| UVC_CTRL_FLAG_AUTO_UPDATE,
},
{
.entity = UVC_GUID_UVC_CAMERA,
.selector = UVC_CT_PANTILT_ABSOLUTE_CONTROL,
.index = 11,
.size = 8,
.flags = UVC_CTRL_FLAG_SET_CUR
| UVC_CTRL_FLAG_GET_RANGE
| UVC_CTRL_FLAG_RESTORE
| UVC_CTRL_FLAG_AUTO_UPDATE,
},
{
.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_MIN
| UVC_CTRL_FLAG_GET_MAX
| UVC_CTRL_FLAG_GET_RES
| UVC_CTRL_FLAG_GET_DEF
| UVC_CTRL_FLAG_AUTO_UPDATE,
}
在这里可以看到这里定义了相对控制和绝对控制的参数,有焦距和上下左右,其中zoom是焦距调节,pan是左右,tilt是上下,缩写是ptz,所以云台摄像头也叫ptz摄像头。
另外需要重点关注的变量是struct uvc_control_mapping uvc_ctrl_mappings[]
,这个结构体枚举出来了所有的控制类型,比如id = V4L2_CID_PAN_ABSOLUTE
和id = V4L2_CID_TILT_ABSOLUTE
的selector等于uvc_ctrls[]中的selector 是UVC_CT_PANTILT_RELATIVE_CONTROL
参数,这两个id分别表示左右和上下的绝对控制,绝对控制的意思是给一个角度,摄像头转到指定的角度之后就停了。焦距的参数与pan和tilt的参数类似。稍微有点不一样的地方是zoom在3.10版本中已经添加了相对和绝对控制,参数id分别为V4L2_CID_ZOOM_ABSOLUTE,V4L2_CID_ZOOM_CONTINUOUS
,其中V4L2_CID_ZOOM_CONTINUOUS
是相对控制,从名称也可以看出continuous是持续的意思,相对控制就是发给摄像头一个参数,摄像头会一直不停的转动,直到最大角度才停止,中途如果给发送了停止位,才会停止。
在这么多控制参数中,重点看一下焦距的相对控制,如下:
{
.id = V4L2_CID_ZOOM_CONTINUOUS,
.name = "Zoom, Continuous",
.entity = UVC_GUID_UVC_CAMERA,
.selector = UVC_CT_ZOOM_RELATIVE_CONTROL,
.size = 0,
.offset = 0,
.v4l2_type = V4L2_CTRL_TYPE_INTEGER,
.data_type = UVC_CTRL_DATA_TYPE_SIGNED,
.get = uvc_ctrl_get_zoom,
.set = uvc_ctrl_set_zoom,
}
看看这个参数中定义了get和set,其实这个是映射到的具体get和set方法,具体方法是:
static __s32 uvc_ctrl_get_zoom(struct uvc_control_mapping *mapping,__u8 query, const __u8 *data)
{
__s8 zoom = (__s8)data[0];
switch (query) {
case UVC_GET_CUR:
return (zoom == 0) ? 0 : (zoom > 0 ? data[2] : -data[2]);
case UVC_GET_MIN:
case UVC_GET_MAX:
case UVC_GET_RES:
case UVC_GET_DEF:
default:
return data[2];
}
}
static void uvc_ctrl_set_zoom(struct uvc_control_mapping *mapping,__s32 value, __u8 *data)
{
data[0] = value == 0 ? 0 : (value > 0) ? 1 : 0xff;
data[2] = min((int)abs(value), 0xff);
}
第一个函数是获取当前焦距所处的位置,在UVC_GET_CUR
处,当前位置为0是,返回0,否则的话大于0,返回当前值,否则返回相反数。
第二个函数是设置zoom的值,data[0]填写的值有三种情况,0,1,0xff,其中0表示停止,1表示拉远,0xff表示拉近。
在这两个函数中可以看到UVC_GET_MIN
和UVC_GET_MAX
,意思是获取最大值和最小值,其实在设备初始化的时候,会将设备的这些各个参数的最大值和最小值读取并保存。
具体取值的地方在__uvc_query_v4l2_ctrl这个函数中,函数定义如下:
static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
struct uvc_control *ctrl,
struct uvc_control_mapping *mapping,
struct v4l2_queryctrl *v4l2_ctrl)
{
struct uvc_control_mapping *master_map = NULL;
struct uvc_control *master_ctrl = NULL;
struct uvc_menu_info *menu;
unsigned int i;
memset(v4l2_ctrl, 0, sizeof *v4l2_ctrl);
v4l2_ctrl->id = mapping->id;
v4l2_ctrl->type = mapping->v4l2_type;
strlcpy(v4l2_ctrl->name, mapping->name, sizeof v4l2_ctrl->name);
v4l2_ctrl->flags = 0;
if (!(ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR))
v4l2_ctrl->flags |= V4L2_CTRL_FLAG_WRITE_ONLY;
if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR))
v4l2_ctrl->flags |= V4L2_CTRL_FLAG_READ_ONLY;
if (mapping->master_id)
__uvc_find_control(ctrl->entity, mapping->master_id,&master_map, &master_ctrl, 0);
if (master_ctrl && (master_ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR)) {
s32 val;
int ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
if (ret < 0)
return ret;
if (val != mapping->master_manual)
v4l2_ctrl->flags |= V4L2_CTRL_FLAG_INACTIVE;
}
if (!ctrl->cached) {
int ret = uvc_ctrl_populate_cache(chain, ctrl);
if (ret < 0)
return ret;
}
if (ctrl->info.flags & UVC_CTRL_FLAG_GET_DEF) {
v4l2_ctrl->default_value = mapping->get(mapping, UVC_GET_DEF,uvc_ctrl_data(ctrl,UVC_CTRL_DATA_DEF));
}
switch (mapping->v4l2_type) {
case V4L2_CTRL_TYPE_MENU:
v4l2_ctrl->minimum = 0;
v4l2_ctrl->maximum = mapping->menu_count - 1;
v4l2_ctrl->step = 1;
menu = mapping->menu_info;
for (i = 0; i < mapping->menu_count; ++i, ++menu) {
if (menu->value == v4l2_ctrl->default_value) {
v4l2_ctrl->default_value = i;
break;
}
}
return 0;
case V4L2_CTRL_TYPE_BOOLEAN:
v4l2_ctrl->minimum = 0;
v4l2_ctrl->maximum = 1;
v4l2_ctrl->step = 1;
return 0;
case V4L2_CTRL_TYPE_BUTTON:
v4l2_ctrl->minimum = 0;
v4l2_ctrl->maximum = 0;
v4l2_ctrl->step = 0;
return 0;
default:
break;
}
if (ctrl->info.flags & UVC_CTRL_FLAG_GET_MIN)
v4l2_ctrl->minimum = mapping->get(mapping, UVC_GET_MIN,uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MIN));
if (ctrl->info.flags & UVC_CTRL_FLAG_GET_MAX)
v4l2_ctrl->maximum = mapping->get(mapping, UVC_GET_MAX,uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MAX));
if (ctrl->info.flags & UVC_CTRL_FLAG_GET_RES)
v4l2_ctrl->step = mapping->get(mapping, UVC_GET_RES,uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES));
return 0;
}
其中结构体v4l2_queryctrl
的定义在\include\uapi\linux\videodev2.h文件中,
struct v4l2_queryctrl {
__u32 id;
__u32 type; /* enum v4l2_ctrl_type */
__u8 name[32]; /* Whatever */
__s32 minimum; /* Note signedness */
__s32 maximum;
__s32 step;
__s32 default_value;
__u32 flags;
__u32 reserved[2];
};
包含了最大值,最小值,步长,默认值,控制名称等信息。
通过传递过来的控制id和类型遍历,并将遍历的结果保存在 v4l2_queryctrl中返回。
顺带说一下,在这个文件下面这个函数也很重要:
int uvc_ctrl_set(struct uvc_video_chain *chain,struct v4l2_ext_control *xctrl)
,这个函数掌控着控制的大权。其中v4l2_ext_control
参数就是上层传递过来的控制参数,非常重要。
从相关控制参数一路分析过来,大致明白了控制的过程和控制代码的逻辑,下一步就是熟悉USB协议之后对这个参数做出定制,以适合不同厂商的摄像头。
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