BananaPi上ov5640摄像头自动对焦功能的实现

经过一段时间的学习，找了很多ov5640的资料，终于把自动对焦功能实现了。

ov5640是一款用在平板和手机上的摄像头，像素为500W，这个像素在目前来讲不算高，中低端手机的像素都比这个高，但是对于学习摄像头驱动开发已经足够了。这次主要的开发和使用平台式BananaPi----基于全志A20双核处理器的平台。使用的软件是linux-sunxi社区的Linux系统。

sunxi的系统中有ov5640的驱动代码，但是这个驱动把ov540的很多功能都阉割了，自动对焦（AutoFocus）功能就在被阉割的功能之列。从ov5640的数据手册和其他的应用手册上来看，自动对焦功能实现需要以下几个步骤：

1、 上电初始化，写入自动对焦固件（firmware）

2、 向控制寄存器写入指定值，开始一次自动对焦过程

3、 等待自动对焦结束，让镜头固定，等待下一次对焦

4、 断电之前让镜头固定在最远处

这里还有一个问题需要注意下，新的摄像头模组上都有一个保护胶膜，把里面的马达粘住了，需要把这个胶膜去掉才能调整焦距。

ov5640和主板连接的方式有很多种，BananaPi上的接口是CSI接口，CSI接口是挂在I2C总线上的，所以，ov5640上寄存器的读写都是通过I2C命令进行的。有关驱动的分析和开发详细信息见全志的说明文档：http://download.csdn.net/detail/longhui173/8074173

驱动的路径为：drivers/media/video/sun4i_csi/device/ov5640.c

根据上面的分析得知，主要修改的地方是初始化部分和sensor_s_ctrl函数部分。在初始化函数中，需要向摄像头模块写入4K的寄存器值，寄存器的值见固件文档：http://download.csdn.net/detail/longhui173/8074193。

初始化部分修改为：

static int sensor_init(struct v4l2_subdev *sd, u32 val)
{
int ret;
csi_dev_dbg("sensor_init\n");

/*Make sure it is a target sensor*/
ret = sensor_detect(sd);
if (ret) {
csi_dev_err("chip found is not an target chip.\n");
return ret;
}
<pre name="code" class="cpp">	ret = sensor_write_array(sd, afc_firmware,ARRAY_SIZE( afc_firmware));			//Simon edit 2014/10/13
if(ret < 0)
{
csi_dev_err("write afc reg error!!\n");
return ret;
}

ret = sensor_write_array(sd, sensor_default_regs , ARRAY_SIZE(sensor_default_regs));if(ret < 0){csi_dev_err("write def array error!!\n");return ret;}csi_dev_print("start write auto focus register\n");return ret;}

其中的afc_firmware就是自动对焦固件的寄存器的值。

sensor_s_ctrl函数修改为：

static int sensor_s_ctrl(struct v4l2_subdev *sd, struct v4l2_control *ctrl)
{
switch (ctrl->id) {
case V4L2_CID_BRIGHTNESS:
return sensor_s_brightness(sd, ctrl->value);
case V4L2_CID_CONTRAST:
return sensor_s_contrast(sd, ctrl->value);
case V4L2_CID_SATURATION:
return sensor_s_saturation(sd, ctrl->value);
case V4L2_CID_HUE:
return sensor_s_hue(sd, ctrl->value);
case V4L2_CID_VFLIP:
return sensor_s_vflip(sd, ctrl->value);
case V4L2_CID_HFLIP:
return sensor_s_hflip(sd, ctrl->value);
case V4L2_CID_GAIN:
return sensor_s_gain(sd, ctrl->value);
case V4L2_CID_AUTOGAIN:
return sensor_s_autogain(sd, ctrl->value);
case V4L2_CID_EXPOSURE:
return sensor_s_exp(sd, ctrl->value);
case V4L2_CID_EXPOSURE_AUTO:
return sensor_s_autoexp(sd,
(enum v4l2_exposure_auto_type) ctrl->value);
case V4L2_CID_DO_WHITE_BALANCE:
return sensor_s_wb(sd,
(enum v4l2_whiteblance) ctrl->value);
case V4L2_CID_AUTO_WHITE_BALANCE:
return sensor_s_autowb(sd, ctrl->value);
case V4L2_CID_COLORFX:
return sensor_s_colorfx(sd,
(enum v4l2_colorfx) ctrl->value);
case V4L2_CID_CAMERA_FLASH_MODE:
return sensor_s_flash_mode(sd,
(enum v4l2_flash_mode) ctrl->value);
case V4L2_CID_FOCUS_AUTO:
return sensor_s_single_af(sd,ctrl->value);
}
return -EINVAL;
}

还需要加入新的函数：sensor_s_single_af()；

static int sensor_s_single_af(struct v4l2_subdev *sd, int value)
{
unsigned char i=0;
int ret;
struct sensor_info *info = to_state(sd);
struct regval_list regs;

csi_dev_print("sensor_s_single_af\n");

regs.reg_num[0] = 0x30;													//Write 0x00 to 0x3000, enable the mcu
regs.reg_num[1] = 0x0;
regs.value[0] = 0x00;
ret = sensor_write(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_write err at start a single af\n");
return ret;
}

regs.reg_num[0] = 0x30;													//set 0x3004 BIT6=1,BIT5=1
regs.reg_num[1] = 0x04;
ret = sensor_read(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_read err at register 0x%x%x\n",regs.reg_num[0],regs.reg_num[1]);
return ret;
}
csi_dev_print("register 0x3004 = 0x%x\n",regs.value[0]);
regs.value[0] |= 0x01 <<5;
regs.value[0] |= 0x01 <<6;
ret = sensor_write(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_write err at register 0x%x%x\n",regs.reg_num[0],regs.reg_num[1]);
return ret;
}

regs.reg_num[0] = 0x30;													//set 0x3001 BIT6=0
regs.reg_num[1] = 0x01;
ret = sensor_read(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_read err at register 0x%x%x\n",regs.reg_num[0],regs.reg_num[1]);
return ret;
}
csi_dev_print("register 0x%x%x = 0x%2x\n",regs.reg_num[0],regs.reg_num[1],regs.value[0]);
regs.value[0] &= ~(0x01 <<6);
ret = sensor_write(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_write err at register 0x%x%x\n",regs.reg_num[0],regs.reg_num[1]);
return ret;
}
regs.reg_num[0] = 0x30;													//set 0x3005 BIT6=1
regs.reg_num[1] = 0x05;
ret = sensor_read(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_read err at register 0x%x%x\n",regs.reg_num[0],regs.reg_num[1]);
return ret;
}
csi_dev_print("register 0x%x%x = 0x%x\n",regs.reg_num[0],regs.reg_num[1],regs.value[0]);
regs.value[0] |= 0x01 <<6;
ret = sensor_write(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_write err at register 0x%x%x\n",regs.reg_num[0],regs.reg_num[1]);
return ret;
}

regs.reg_num[0] = 0x30;													//Write 0x03 to 0x3022, start singal af
regs.reg_num[1] = 0x22;
regs.value[0] = 0x03;
ret = sensor_write(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_write err at start a single af\n");
return ret;
}
while(regs.value[0] !=0 && i < 50)
{
i++;
msleep(100);
ret = sensor_read(sd, regs.reg_num, regs.value);
if (ret < 0) {
csi_dev_err("sensor_read err at sensor_s_single_af!\n");
return ret;
}
csi_dev_print("register 0x3022=0x%x\n",regs.value[0]);
}
if( i >= 50)
{
csi_dev_print("write 0x03 to 0x3022 timeout!!\n");
return -1;
}
i = 0;
regs.reg_num[0] = 0x30;
regs.reg_num[1] = 0x29;
//regs.value[0] = 0x10;
while(regs.value[0] != 0x10 && i < 200)
{
msleep(500);
ret = sensor_read(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_read err at sensor_s_single_af!\n");
return -1;
}
csi_dev_print("register 0x3029=0x%x\n",regs.value[0]);
i++;
}
if(i >= 200)
{
csi_dev_err("sensor_s_single_af failed\n");
return -1;
}
csi_dev_print("Single AF ok ,value = 0x10\n");

regs.reg_num[0] = 0x30;
regs.reg_num[1] = 0x22;
regs.value[0] = 0x06;
ret = sensor_write(sd,regs.reg_num,regs.value);
if(ret < 0)
{
csi_dev_err("sensor_write err at pause af\n");
return ret;
}
return 0;
}

这个函数中间很多代码都是为了调试所用。

在应用程序中，在需要自动对焦的地方调用函数：

struct v4l2_ext_control  control;
CLEAR(control);
control.id = V4L2_CID_FOCUS_AUTO;//V4L2_CID_EXPOSURE_AUTO;
if (-1 == ioctl(fd, VIDIOC_S_CTRL, &control)) {
perror("VIDIOC_S_CTRL");
exit(EXIT_FAILURE);

}

这样就可以实现ov5640的自动对焦了。