Chinaunix首页 | 论坛 | 博客

hushup的ChinaUnix博客

首页　| 　博文目录　| 　关于我

hushup

  • 博客访问： 336516
  • 博文数量： 108
  • 博客积分： 0
  • 博客等级： 民兵
  • 技术积分： 65
  • 用 户 组： 普通用户
  • 注册时间： 2013-12-16 11:38
文章分类

全部博文（108）

文章存档

2016年（2）

2015年（44）

2014年（62）

我的朋友
最近访客
推荐博文
相关博文
以vivi.c为例分析摄像头驱动程序思路

分类： 嵌入式

2015-10-13 21:20:17

原文地址：以vivi.c为例分析摄像头驱动程序思路 作者：rxlinux


点击(此处)折叠或打开

  1. 以vivi.c为例分析摄像头驱动程序思路：
  2. Virtual Video driver - This code emulates a real video device with v4l2 api

  4. 入口：static int __init vivi_init(void)
  5.           ret = vivi_create_instance(i) //创建设备
  6.                    struct vivi_dev *dev; //定义一个vivi_dev结构体
  7.       (a)定义 struct video_device *vfd //定义一个video_devce结构体
  8. struct vivi_dev {
  9.     struct list_head vivi_devlist;
  10.     struct v4l2_device      v4l2_dev;

  12.     spinlock_t slock;
  13.     struct mutex         mutex;

  15.     int users;

  17.     /* various device info */
  18.     struct video_device *vfd;

  20.     struct vivi_dmaqueue vidq;

  22.     /* Several counters */
  23.     int h, m, s, ms;
  24.     unsigned long jiffies;
  25.     char timestr[13];

  27.     int             mv_count;    /* Controls bars movement */

  29.     /* Input Number */
  30.     int             input;

  32.     /* Control 'registers' */
  33.     int              qctl_regs[ARRAY_SIZE(vivi_qctrl)];
  34. };
  35. 重要成员：
  36. /* various device info */
  37.     struct video_device *vfd; //套接一个video_devce结构体，里面设置设备信息
  38. struct video_device
  39. {
  40.     const struct v4l2_file_operations *fops;

  42.     /* sysfs */
  43.     struct device dev;        /* v4l device */
  44.     struct cdev *cdev;        /* character device */

  46.     /* Set either parent or v4l2_dev if your driver uses v4l2_device */
  47.     struct device *parent;        /* device parent */
  48.     struct v4l2_device *v4l2_dev;    /* v4l2_device parent */

  50.     /* device info */
  51.     char name[32];
  52.     int vfl_type;
  53.     /* 'minor' is set to -1 if the registration failed */
  54.     int minor;
  55.     u16 num;
  56.     /* use bitops to set/clear/test flags */
  57.     unsigned long flags;
  58.     /* attribute to differentiate multiple indices on one physical device */
  59.     int index;

  61.     int debug;            /* Activates debug level*/

  63.     /* Video standard vars */
  64.     v4l2_std_id tvnorms;        /* Supported tv norms */
  65.     v4l2_std_id current_norm;    /* Current tvnorm */

  67.     /* callbacks */
  68.     void (*release)(struct video_device *vdev);

  70.     
  71.     const struct v4l2_ioctl_ops *ioctl_ops;
  72. };
  73. 重要成员：
  74.     const struct v4l2_file_operations *fops; //定义设备操作函数
  75.     const struct v4l2_ioctl_ops *ioctl_ops; //定义ioctl 回调函数，用于应用程序获取底层信息比如获取、配置摄像头所支持的格式
  76.     
  77. vivi.c中对video_device设置的过程：
  78.       (b)分配    vfd = video_device_alloc(); //给前面定义的video_device结构体分配内存
  79.       (c)设置    *vfd = vivi_template; //把之前设置好的video_device结构体赋给vfd
  80. 注：
  81. static struct video_device vivi_template = {
  82.     .name        = "vivi",
  83.     .fops = &vivi_fops,
  84.     .ioctl_ops     = &vivi_ioctl_ops,
  85.     .minor        = -1,
  86.     .release    = video_device_release,
  87. 其中包括几个两个重要操作函数的设置：
  88. 1.
  89. static const struct v4l2_file_operations vivi_fops = {
  90.     .owner        = THIS_MODULE,
  91.     .open = vivi_open,
  92.     .release = vivi_close,
  93.     .read = vivi_read,
  94.     .poll        = vivi_poll,
  95.     .ioctl = video_ioctl2, /* V4L2 ioctl handler */
  96.     .mmap = vivi_mmap,
  97. };


  100. struct v4l2_file_operations {
  101.     struct module *owner;
  102.     ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
  103.     ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
  104.     unsigned int (*poll) (struct file *, struct poll_table_struct *);
  105.     long (*ioctl) (struct file *, unsigned int, unsigned long);
  106.     long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
  107.     unsigned long (*get_unmapped_area) (struct file *, unsigned long,
  108.                 unsigned long, unsigned long, unsigned long);
  109.     int (*mmap) (struct file *, struct vm_area_struct *);
  110.     int (*open) (struct file *);
  111.     int (*release) (struct file *);
  112. };
  113. 2.
  114. static const struct v4l2_ioctl_ops vivi_ioctl_ops = {
  115.     /* 表示它是一个摄像头设备 */
  116.     .vidioc_querycap = vidioc_querycap,
  117.         
  118.     /* 用于选择输入源，在xawtv里面就是video source */    
  119.     //.vidioc_enum_input = vidioc_enum_input,    
  120.     //.vidioc_g_input = vidioc_g_input,
  121.     //.vidioc_s_input = vidioc_s_input,
  122.     
  123.     /* 用于列举、获得TV 制式，不是必须的*/
  124.     //.vidioc_s_std = vidioc_s_std,
  125.     /* video_device里面:
  126.      .tvnorms = V4L2_STD_525_60, //用于IDIOC_ENUMSTD
  127.      .current_norm = V4L2_STD_NTSC_M,// 用于VIDIOC_G_STD
  128.      */

  130.     /* 用于列举、获得、测试、设置摄像头所提供的格式 */
  131.     .vidioc_enum_fmt_vid_cap = vidioc_enum_fmt_vid_cap,//也可以去掉
  132.     .vidioc_g_fmt_vid_cap = vidioc_g_fmt_vid_cap,
  133.     .vidioc_try_fmt_vid_cap = vidioc_try_fmt_vid_cap,
  134.     .vidioc_s_fmt_vid_cap = vidioc_s_fmt_vid_cap,

  136.     /* 缓冲区操作: 申请/ 查询/ 放入队列/取出队列*/
  137.     .vidioc_reqbufs = vidioc_reqbufs,
  138.     .vidioc_querybuf = vidioc_querybuf,
  139.     .vidioc_qbuf = vidioc_qbuf,
  140.     .vidioc_dqbuf = vidioc_dqbuf,
  141.     
  142.     /* 查询/获得/设置属性 */
  143.     //.vidioc_queryctrl = vidioc_queryctrl,
  144.     //.vidioc_g_ctrl = vidioc_g_ctrl,
  145.     //.vidioc_s_ctrl = vidioc_s_ctrl,

  147.     /* 启动/停止摄像头 */
  148.     .vidioc_streamon = vidioc_streamon,
  149.     .vidioc_streamoff = vidioc_streamoff,
  150. };


  153. struct v4l2_ioctl_ops {
  154.     /* ioctl callbacks */

  156.     /* VIDIOC_QUERYCAP handler */
  157.     int (*vidioc_querycap)(struct file *file, void *fh, struct v4l2_capability *cap);

  159.     /* Priority handling */
  160.     int (*vidioc_g_priority) (struct file *file, void *fh,
  161.                  enum v4l2_priority *p);
  162.     int (*vidioc_s_priority) (struct file *file, void *fh,
  163.                  enum v4l2_priority p);

  165.     /* VIDIOC_ENUM_FMT handlers */
  166.     int (*vidioc_enum_fmt_vid_cap) (struct file *file, void *fh,
  167.                      struct v4l2_fmtdesc *f);
  168.     int (*vidioc_enum_fmt_vid_overlay) (struct file *file, void *fh,
  169.                      struct v4l2_fmtdesc *f);
  170.     int (*vidioc_enum_fmt_vid_out) (struct file *file, void *fh,
  171.                      struct v4l2_fmtdesc *f);
  172.     int (*vidioc_enum_fmt_type_private)(struct file *file, void *fh,
  173.                      struct v4l2_fmtdesc *f);

  175.     /* VIDIOC_G_FMT handlers */
  176.     int (*vidioc_g_fmt_vid_cap) (struct file *file, void *fh,
  177.                     struct v4l2_format *f);
  178.     int (*vidioc_g_fmt_vid_overlay)(struct file *file, void *fh,
  179.                     struct v4l2_format *f);
  180.     int (*vidioc_g_fmt_vid_out) (struct file *file, void *fh,
  181.                     struct v4l2_format *f);
  182.     int (*vidioc_g_fmt_vid_out_overlay)(struct file *file, void *fh,
  183.                     struct v4l2_format *f);
  184.     int (*vidioc_g_fmt_vbi_cap) (struct file *file, void *fh,
  185.                     struct v4l2_format *f);
  186.     int (*vidioc_g_fmt_vbi_out) (struct file *file, void *fh,
  187.                     struct v4l2_format *f);
  188.     int (*vidioc_g_fmt_sliced_vbi_cap)(struct file *file, void *fh,
  189.                     struct v4l2_format *f);
  190.     int (*vidioc_g_fmt_sliced_vbi_out)(struct file *file, void *fh,
  191.                     struct v4l2_format *f);
  192.     int (*vidioc_g_fmt_type_private)(struct file *file, void *fh,
  193.                     struct v4l2_format *f);

  195.     /* VIDIOC_S_FMT handlers */
  196.     int (*vidioc_s_fmt_vid_cap) (struct file *file, void *fh,
  197.                     struct v4l2_format *f);
  198.     int (*vidioc_s_fmt_vid_overlay)(struct file *file, void *fh,
  199.                     struct v4l2_format *f);
  200.     int (*vidioc_s_fmt_vid_out) (struct file *file, void *fh,
  201.                     struct v4l2_format *f);
  202.     int (*vidioc_s_fmt_vid_out_overlay)(struct file *file, void *fh,
  203.                     struct v4l2_format *f);
  204.     int (*vidioc_s_fmt_vbi_cap) (struct file *file, void *fh,
  205.                     struct v4l2_format *f);
  206.     int (*vidioc_s_fmt_vbi_out) (struct file *file, void *fh,
  207.                     struct v4l2_format *f);
  208.     int (*vidioc_s_fmt_sliced_vbi_cap)(struct file *file, void *fh,
  209.                     struct v4l2_format *f);
  210.     int (*vidioc_s_fmt_sliced_vbi_out)(struct file *file, void *fh,
  211.                     struct v4l2_format *f);
  212.     int (*vidioc_s_fmt_type_private)(struct file *file, void *fh,
  213.                     struct v4l2_format *f);

  215.     /* VIDIOC_TRY_FMT handlers */
  216.     int (*vidioc_try_fmt_vid_cap) (struct file *file, void *fh,
  217.                      struct v4l2_format *f);
  218.     int (*vidioc_try_fmt_vid_overlay)(struct file *file, void *fh,
  219.                      struct v4l2_format *f);
  220.     int (*vidioc_try_fmt_vid_out) (struct file *file, void *fh,
  221.                      struct v4l2_format *f);
  222.     int (*vidioc_try_fmt_vid_out_overlay)(struct file *file, void *fh,
  223.                      struct v4l2_format *f);
  224.     int (*vidioc_try_fmt_vbi_cap) (struct file *file, void *fh,
  225.                      struct v4l2_format *f);
  226.     int (*vidioc_try_fmt_vbi_out) (struct file *file, void *fh,
  227.                      struct v4l2_format *f);
  228.     int (*vidioc_try_fmt_sliced_vbi_cap)(struct file *file, void *fh,
  229.                      struct v4l2_format *f);
  230.     int (*vidioc_try_fmt_sliced_vbi_out)(struct file *file, void *fh,
  231.                      struct v4l2_format *f);
  232.     int (*vidioc_try_fmt_type_private)(struct file *file, void *fh,
  233.                      struct v4l2_format *f);

  235.     /* Buffer handlers */
  236.     int (*vidioc_reqbufs) (struct file *file, void *fh, struct v4l2_requestbuffers *b);
  237.     int (*vidioc_querybuf)(struct file *file, void *fh, struct v4l2_buffer *b);
  238.     int (*vidioc_qbuf) (struct file *file, void *fh, struct v4l2_buffer *b);
  239.     int (*vidioc_dqbuf) (struct file *file, void *fh, struct v4l2_buffer *b);


  242.     int (*vidioc_overlay) (struct file *file, void *fh, unsigned int i);
  243. #ifdef CONFIG_VIDEO_V4L1_COMPAT
  244.             /* buffer type is struct vidio_mbuf * */
  245.     int (*vidiocgmbuf) (struct file *file, void *fh, struct video_mbuf *p);
  246. #endif
  247.     int (*vidioc_g_fbuf) (struct file *file, void *fh,
  248.                 struct v4l2_framebuffer *a);
  249.     int (*vidioc_s_fbuf) (struct file *file, void *fh,
  250.                 struct v4l2_framebuffer *a);

  252.         /* Stream on/off */
  253.     int (*vidioc_streamon) (struct file *file, void *fh, enum v4l2_buf_type i);
  254.     int (*vidioc_streamoff)(struct file *file, void *fh, enum v4l2_buf_type i);

  256.         /* Standard handling
  257.             ENUMSTD is handled by videodev.c
  258.          */
  259.     int (*vidioc_g_std) (struct file *file, void *fh, v4l2_std_id *norm);
  260.     int (*vidioc_s_std) (struct file *file, void *fh, v4l2_std_id *norm);
  261.     int (*vidioc_querystd) (struct file *file, void *fh, v4l2_std_id *a);

  263.         /* Input handling */
  264.     int (*vidioc_enum_input)(struct file *file, void *fh,
  265.                  struct v4l2_input *inp);
  266.     int (*vidioc_g_input) (struct file *file, void *fh, unsigned int *i);
  267.     int (*vidioc_s_input) (struct file *file, void *fh, unsigned int i);

  269.         /* Output handling */
  270.     int (*vidioc_enum_output) (struct file *file, void *fh,
  271.                  struct v4l2_output *a);
  272.     int (*vidioc_g_output) (struct file *file, void *fh, unsigned int *i);
  273.     int (*vidioc_s_output) (struct file *file, void *fh, unsigned int i);

  275.         /* Control handling */
  276.     int (*vidioc_queryctrl) (struct file *file, void *fh,
  277.                     struct v4l2_queryctrl *a);
  278.     int (*vidioc_g_ctrl) (struct file *file, void *fh,
  279.                     struct v4l2_control *a);
  280.     int (*vidioc_s_ctrl) (struct file *file, void *fh,
  281.                     struct v4l2_control *a);
  282.     int (*vidioc_g_ext_ctrls) (struct file *file, void *fh,
  283.                     struct v4l2_ext_controls *a);
  284.     int (*vidioc_s_ext_ctrls) (struct file *file, void *fh,
  285.                     struct v4l2_ext_controls *a);
  286.     int (*vidioc_try_ext_ctrls) (struct file *file, void *fh,
  287.                     struct v4l2_ext_controls *a);
  288.     int (*vidioc_querymenu) (struct file *file, void *fh,
  289.                     struct v4l2_querymenu *a);

  291.     /* Audio ioctls */
  292.     int (*vidioc_enumaudio) (struct file *file, void *fh,
  293.                     struct v4l2_audio *a);
  294.     int (*vidioc_g_audio) (struct file *file, void *fh,
  295.                     struct v4l2_audio *a);
  296.     int (*vidioc_s_audio) (struct file *file, void *fh,
  297.                     struct v4l2_audio *a);

  299.     /* Audio out ioctls */
  300.     int (*vidioc_enumaudout) (struct file *file, void *fh,
  301.                     struct v4l2_audioout *a);
  302.     int (*vidioc_g_audout) (struct file *file, void *fh,
  303.                     struct v4l2_audioout *a);
  304.     int (*vidioc_s_audout) (struct file *file, void *fh,
  305.                     struct v4l2_audioout *a);
  306.     int (*vidioc_g_modulator) (struct file *file, void *fh,
  307.                     struct v4l2_modulator *a);
  308.     int (*vidioc_s_modulator) (struct file *file, void *fh,
  309.                     struct v4l2_modulator *a);
  310.     /* Crop ioctls */
  311.     int (*vidioc_cropcap) (struct file *file, void *fh,
  312.                     struct v4l2_cropcap *a);
  313.     int (*vidioc_g_crop) (struct file *file, void *fh,
  314.                     struct v4l2_crop *a);
  315.     int (*vidioc_s_crop) (struct file *file, void *fh,
  316.                     struct v4l2_crop *a);
  317.     /* Compression ioctls */
  318.     int (*vidioc_g_jpegcomp) (struct file *file, void *fh,
  319.                     struct v4l2_jpegcompression *a);
  320.     int (*vidioc_s_jpegcomp) (struct file *file, void *fh,
  321.                     struct v4l2_jpegcompression *a);
  322.     int (*vidioc_g_enc_index) (struct file *file, void *fh,
  323.                     struct v4l2_enc_idx *a);
  324.     int (*vidioc_encoder_cmd) (struct file *file, void *fh,
  325.                     struct v4l2_encoder_cmd *a);
  326.     int (*vidioc_try_encoder_cmd) (struct file *file, void *fh,
  327.                     struct v4l2_encoder_cmd *a);

  329.     /* Stream type-dependent parameter ioctls */
  330.     int (*vidioc_g_parm) (struct file *file, void *fh,
  331.                     struct v4l2_streamparm *a);
  332.     int (*vidioc_s_parm) (struct file *file, void *fh,
  333.                     struct v4l2_streamparm *a);

  335.     /* Tuner ioctls */
  336.     int (*vidioc_g_tuner) (struct file *file, void *fh,
  337.                     struct v4l2_tuner *a);
  338.     int (*vidioc_s_tuner) (struct file *file, void *fh,
  339.                     struct v4l2_tuner *a);
  340.     int (*vidioc_g_frequency) (struct file *file, void *fh,
  341.                     struct v4l2_frequency *a);
  342.     int (*vidioc_s_frequency) (struct file *file, void *fh,
  343.                     struct v4l2_frequency *a);

  345.     /* Sliced VBI cap */
  346.     int (*vidioc_g_sliced_vbi_cap) (struct file *file, void *fh,
  347.                     struct v4l2_sliced_vbi_cap *a);

  349.     /* Log status ioctl */
  350.     int (*vidioc_log_status) (struct file *file, void *fh);

  352.     int (*vidioc_s_hw_freq_seek) (struct file *file, void *fh,
  353.                     struct v4l2_hw_freq_seek *a);

  355.     /* Debugging ioctls */
  356. #ifdef CONFIG_VIDEO_ADV_DEBUG
  357.     int (*vidioc_g_register) (struct file *file, void *fh,
  358.                     struct v4l2_dbg_register *reg);
  359.     int (*vidioc_s_register) (struct file *file, void *fh,
  360.                     struct v4l2_dbg_register *reg);
  361. #endif
  362.     int (*vidioc_g_chip_ident) (struct file *file, void *fh,
  363.                     struct v4l2_dbg_chip_ident *chip);

  365.     int (*vidioc_enum_framesizes) (struct file *file, void *fh,
  366.                      struct v4l2_frmsizeenum *fsize);

  368.     int (*vidioc_enum_frameintervals) (struct file *file, void *fh,
  369.                      struct v4l2_frmivalenum *fival);

  371.     /* For other private ioctls */
  372.     long (*vidioc_default)     (struct file *file, void *fh,
  373.                     int cmd, void *arg);
  374. };    
  375.     (d)注册     ret = video_register_device(vfd, VFL_TYPE_GRABBER, video_nr);
  376.                  return video_register_device_index(vdev, type, nr, -1);
  377.                          /*注册三部曲*/
  378.                          vdev->cdev = cdev_alloc(); //第一步 分配字符设备内存
  379.                          vdev->cdev->ops = &v4l2_fops; //第二部 设置将设备节点的操作函数
  380.                          ret = cdev_add(vdev->cdev, MKDEV(VIDEO_MAJOR, vdev->minor), 1); //将字符设备注册进内核
  381. 以上是虚拟视频驱动vivi.c的分析，以下下是分析vivi.c的open,read,write,ioctl过程：
  382. 1. open
  383. app: open(/dev/video0)

  385. 2. read
  386. app: read(/dev/video0)

  388. 3. write
  389. app: write(/dev/video0)     
  390. 4. ioctl
  391. app: iotcl(/dev/video0)
  392.   
  393.   以上系统函数调用，在进入驱动程序里都对应上面注册的v4l2_fops结构体里面的对应函数：
  394.  static const struct file_operations v4l2_fops = {
  395.      .owner = THIS_MODULE,
  396.     .read = v4l2_read,
  397.     .write = v4l2_write,
  398.     .open = v4l2_open,
  399.     .get_unmapped_area = v4l2_get_unmapped_area,
  400.     .mmap = v4l2_mmap,
  401.     .ioctl = v4l2_ioctl,    


  404. static int v4l2_open(struct inode *inode, struct file *filp)
  405. {
  406.     struct video_device *vdev;
  407.     int ret = 0;

  409.     /* Check if the video device is available */
  410.     mutex_lock(&videodev_lock);
  411.     vdev = video_devdata(filp); // 根据次设备号从数组中得到video_device
  412.     /* return ENODEV if the video device has been removed
  413.      already or if it is not registered anymore. */
  414.     if (vdev == NULL || video_is_unregistered(vdev)) {
  415.         mutex_unlock(&videodev_lock);
  416.         return -ENODEV;
  417.     }
  418.     /* and increase the device refcount */
  419.     video_get(vdev);
  420.     mutex_unlock(&videodev_lock);
  421.     if (vdev->fops->open)
  422.         ret = vdev->fops->open(filp); //这里才显示庐山真面目，最终调用的是前面写的vivi_open函数

  424.     /* decrease the refcount in case of an error */
  425.     if (ret)
  426.         video_put(vdev);
  427.     return ret;    
  428. }
  429. 注：
  430. struct video_device *video_devdata(struct file *file)
  431. {
  432.     return video_device[iminor(file->f_path.dentry->d_inode)];
  433.     
  434. }
  435. 同理：app中的read函数最终会调用v4l2_read函数：
  436. static ssize_t v4l2_read(struct file *filp, char __user *buf,
  437.         size_t sz, loff_t *off)
  438. {
  439.     struct video_device *vdev = video_devdata(filp);

  441.     if (!vdev->fops->read)
  442.         return -EINVAL;
  443.     if (video_is_unregistered(vdev))
  444.         return -EIO;
  445.     return vdev->fops->read(filp, buf, sz, off); //最终会调用v4l2_fops操作结构体中的vivi_read函数
  446. }
  447. 注：由于采用总线设备驱动模型，一些驱动通用的函数，linux系统已经帮助实现v4l2_dev.c（例v4l2_fops）,到具体open,read,write，ioctl时，即最终
  448. 的open,read,write,ioctl等函数还要写驱动的人实现。

  450. static ssize_t v4l2_write(struct file *filp, const char __user *buf,
  451.         size_t sz, loff_t *off)
  452. {
  453.     struct video_device *vdev = video_devdata(filp);

  455.     if (!vdev->fops->write)
  456.         return -EINVAL;
  457.     if (video_is_unregistered(vdev))
  458.         return -EIO;
  459.     return vdev->fops->write(filp, buf, sz, off);//最终会调用v4l2_fops操作结构体中的vivi_write函数
  460. }

  462. static int v4l2_ioctl(struct inode *inode, struct file *filp,
  463.         unsigned int cmd, unsigned long arg)
  464. {
  465.     struct video_device *vdev = video_devdata(filp);

  467.     if (!vdev->fops->ioctl)
  468.         return -ENOTTY;
  469.     /* Allow ioctl to continue even if the device was unregistered.
  470.      Things like dequeueing buffers might still be useful. */
  471.     return vdev->fops->ioctl(filp, cmd, arg); //最终会调用v4l2_fops操作结构体中的vivi_ioctl函数

阅读(1240) | 评论(0) | 转发(0) |
0

上一篇：虚拟视频驱动程序vivi.c源码分析

下一篇：Device Tree Usage

给主人留下些什么吧！~~
关于我们 | 关于IT168 | 联系方式 | 广告合作 | 法律声明 | 免费注册

Copyright 2001-2010 ChinaUnix.net All Rights Reserved 北京皓辰网域网络信息技术有限公司. 版权所有

感谢所有关心和支持过ChinaUnix的朋友们

16024965号-6