Spac5xx的实现是按照标准的USB VIDEO设备的驱动框架编写(其具体的驱动框架可参照/usr/src/linux/drivers/usb/usbvideo.c文件),整个源程序由四个主体部分组成:
设备模块的初始化模块和卸载模块,上层软件接口模块,数据传输模块。
具体的模块分析如下:
一、初始化设备模块
该驱动采用了显式的模块初始化和消除函数,即调用module_init来初始化一个模块,并在卸载时调用moduel-exit函数
其具体实现如下:
1、模块初始化:
- module_init (usb_spca5xx_init);
- static int __init usb_spca5xx_init (void)
- {
- #ifdef CONFIG_PROC_FS
- proc_spca50x_create ();//建立PROC设备文件
- #endif /* CONFIG_PROC_FS */
- if (usb_register (&spca5xx_driver) < 0) //注册USB设备驱动
- return -1;
- info ("spca5xx driver %s registered", version);
- return 0;
- }
2、模块卸载:
- module_exit (usb_spca5xx_exit);
- static void __exit usb_spca5xx_exit (void)
- {
- usb_deregister (&spca5xx_driver); //注销USB设备驱动
- info ("driver spca5xx deregistered");
- #ifdef CONFIG_PROC_FS
- proc_spca50x_destroy ();//撤消PROC设备文件
- #endif /* CONFIG_PROC_FS */
- }
关键数据结构 USB驱动结构,即插即用功能的实现
- static struct usb_driver spca5xx_driver = {
- "spca5xx",
- spca5xx_probe, //注册设备自我侦测功能
- spca5xx_disconnect,//注册设备自我断开功能
- {NULL,NULL}
- };
用两个函数调用spca5xx_probe 和spca5xx_disconnect来支持USB设备的即插即用功能:
a -- spca5xx_probe 具体实现如下:
- static void * spca5xx_probe (struct usb_device *dev, unsigned int ifnum, const struct usb_device_id *id)
- {
- struct usb_interface_descriptor *interface; //USB设备接口描述符
- struct usb_spca50x *spca50x; //物理设备数据结构
- int err_probe;
- int i;
- if (dev->descriptor.bNumConfigurations != 1) //探测设备是不是可配置
- goto nodevice;
- if (ifnum > 0)
- goto nodevice;
- interface = &dev->actconfig->interface[ifnum].altsetting[0];
- MOD_INC_USE_COUNT;
- interface = &intf->altsetting[0].desc;
- if (interface->bInterfaceNumber > 0)
- goto nodevice;
- if ((spca50x = kmalloc (sizeof (struct usb_spca50x), GFP_KERNEL)) == NULL) //分配物理地址空间
- {
- err ("couldn't kmalloc spca50x struct");
- goto error;
- }
- memset (spca50x, 0, sizeof (struct usb_spca50x));
- spca50x->dev = dev;
- spca50x->iface = interface->bInterfaceNumber;
- if ((err_probe = spcaDetectCamera (spca50x)) < 0) //具体物理设备查找,匹配厂商号,设备号(在子程序中)
- {
- err (" Devices not found !! ");
- goto error;
- }
- PDEBUG (0, "Camera type %s ", Plist[spca50x->cameratype].name)
- for (i = 0; i < SPCA50X_NUMFRAMES; i++)
- init_waitqueue_head (&spca50x->frame[i].wq); //初始化帧等待队列
- init_waitqueue_head (&spca50x->wq); //初始化驱动等待队列
- if (!spca50x_configure (spca50x)) //物理设备配置(主要完成传感器侦测和图形参数配置),主要思想是给控制寄存器写值,读回其返回值,以此判断具体的传感器型号
- {
- spca50x->user = 0;
- init_MUTEX (&spca50x->lock); //信号量初始化
- init_MUTEX (&spca50x->buf_lock);
- spca50x->v4l_lock = SPIN_LOCK_UNLOCKED;
- spca50x->buf_state = BUF_NOT_ALLOCATED;
- }
- else
- {
- err ("Failed to configure camera");
- goto error;
- }
- /* Init video stuff */
- spca50x->vdev = video_device_alloc (); //设备控制块内存分配
- if (!spca50x->vdev)
- goto error;
- memcpy (spca50x->vdev, &spca50x_template, sizeof (spca50x_template));
- //系统调用的挂接,在此将驱动实现的系统调用,挂到内核中
- video_set_drvdata (spca50x->vdev, spca50x);
- if (video_register_device (spca50x->vdev, VFL_TYPE_GRABBER, video_nr) < 0)
- {
- //video设备注册
- err ("video_register_device failed");
- goto error;
- }
- spca50x->present = 1;
- if (spca50x->force_rgb)
- info ("data format set to RGB");
- spca50x->task.sync = 0;
- spca50x->task.routine = auto_bh;
- spca50x->task.data = spca50x;
- spca50x->bh_requested = 0;
- MOD_DEC_USE_COUNT; //增加模块使用数
- return spca50x; //返回数剧结构
- error://错误处理
- if (spca50x->vdev)
- {
- if (spca50x->vdev->minor == -1)
- video_device_release (spca50x->vdev);
- else
- video_unregister_device (spca50x->vdev);
- spca50x->vdev = NULL;
- }
- if (spca50x)
- {
- kfree (spca50x);
- spca50x = NULL;
- }
- MOD_DEC_USE_COUNT;
- return NULL;
- nodevice:
- return NULL;
- }
- static void spca5xx_disconnect (struct usb_device *dev, void *ptr)
- {
- struct usb_spca50x *spca50x = (struct usb_spca50x *) ptr;
- int n;
- MOD_INC_USE_COUNT; //增加模块使用数
- if (!spca50x)
- return;
- down (&spca50x->lock); //减少信号量
- spca50x->present = 0; //驱动卸载置0
- for (n = 0; n < SPCA50X_NUMFRAMES; n++) //标示所有帧ABORTING状态
- {
- spca50x->frame[n].grabstate = FRAME_ABORTING;
- spca50x->curframe = -1;
- }
- for (n = 0; n < SPCA50X_NUMFRAMES; n++) //唤醒所有等待进程
- {
- if (waitqueue_active (&spca50x->frame[n].wq))
- wake_up_interruptible (&spca50x->frame[n].wq);
- if (waitqueue_active (&spca50x->wq))
- wake_up_interruptible (&spca50x->wq);
- }
- spca5xx_kill_isoc(spca50x); //子函数终止URB包的传输
- PDEBUG (3,"Disconnect Kill isoc done");
- up (&spca50x->lock); //增加信号量
- while(spca50x->user) /如果还有进程在使用,进程切换
- schedule();
- down (&spca50x->lock);
- if (spca50x->vdev)
- {
- video_unregister_device (spca50x->vdev); //注销video设备
- usb_driver_release_interface (&spca5xx_driver,&spca50x->dev->actconfig->interface[spca50x->iface]); //端口释放
- spca50x->dev = NULL;
- }
- up (&spca50x->lock);
- #ifdef CONFIG_PROC_FS
- destroy_proc_spca50x_cam (spca50x); //注销PROC文件
- #endif /* CONFIG_PROC_FS */
- if (spca50x && !spca50x->user) //释放内存空间
- {
- spca5xx_dealloc (spca50x);
- kfree (spca50x);
- spca50x = NULL;
- }
- MOD_DEC_USE_COUNT; //减少模块记数
- PDEBUG (3, "Disconnect complete");
- }
该模块通过file_operations数据结构,依据V4L协议规范,实现设备的关键系统调用,实现设备文件化的UNIX系统设计特点。作为摄相头驱动,其功能在于数据采集,而没有向摄相头输出的功能,因此在源码中没有实现write系统调用。
其关键的数据结构如下:
- static struct video_device spca50x_template = {
- .owner = THIS_MODULE,
- .name = "SPCA5XX USB Camera",
- .type = VID_TYPE_CAPTURE,
- .hardware = VID_HARDWARE_SPCA5XX,
- .fops = &spca5xx_fops,
- };
- static struct file_operations spca5xx_fops = {
- .owner = THIS_MODULE,
- .open = spca5xx_open, //open功能
- .release = spca5xx_close,//close功能
- .read = spca5xx_read, //read功能
- .mmap = spca5xx_mmap, //内存映射功能
- .ioctl = spca5xx_ioctl, //文件信息获取
- .llseek = no_llseek,//文件定位功能未实现
- };
1. Open功能
完成设备的打开和初始化,并初始化解码器模块。其具体实现如下:
- static int spca5xx_open(struct video_device *vdev, int flags)
- {
- struct usb_spca50x *spca50x = video_get_drvdata (vdev);
- int err;
- MOD_INC_USE_COUNT; //增加模块记数
- down (&spca50x->lock);
- err = -ENODEV;
- if (!spca50x->present) //检查设备是不是存在,有不有驱动,是不是忙
- goto out;
- err = -EBUSY;
- if (spca50x->user)
- goto out;
- err = -ENOMEM;
- if (spca50x_alloc (spca50x))
- goto out;
- err = spca50x_init_source (spca50x); //初始化传感器和解码模块,在此函数的实现中,对每一款DSP芯片的初始化都不一样,对中星微301P的DSP芯片的初始化在子函数zc3xx_init,其实现方法为寄存器填值。
- if (err != 0)
- {
- PDEBUG (0, "DEALLOC error on spca50x_init_source\n");
- up (&spca50x->lock);
- spca5xx_dealloc (spca50x);
- goto out2;
- }
- spca5xx_initDecoder(spca50x); //解码模块初始化,其模块的具体实现采用的是huffman算法 spca5xx_setFrameDecoder(spca50x);
- spca50x->user++;
- err = spca50x_init_isoc (spca50x); //初始化URB(usb request block) 包,启动摄相头,采用同步传输的方式传送数据
- if (err)
- {
- PDEBUG (0, " DEALLOC error on init_Isoc\n");
- spca50x->user--;
- spca5xx_kill_isoc (spca50x);
- up (&spca50x->lock);
- spca5xx_dealloc (spca50x);
- goto out2;
- }
- spca50x->brightness = spca50x_get_brghtness (spca50x) << 8;
- spca50x->whiteness = 0;
- out:
- up (&spca50x->lock);
- out2:
- if (err)
- MOD_DEC_USE_COUNT;
- if (err)
- {
- PDEBUG (2, "Open failed");
- }
- else
- {
- PDEBUG (2, "Open done");
- }
- return err;
- }
2.Close功能
完成设备的关闭,其具体过程是:
- static void spca5xx_close(struct video_device *vdev)
- {
- struct usb_spca50x *spca50x =vdev->priv;
- int i;
- PDEBUG (2, "spca50x_close");
- down (&spca50x->lock); //参数设置
- spca50x->user--;
- spca50x->curframe = -1;
- if(spca50x->present)//present:是或有驱动加载
- {
- spca50x_stop_isoc (spca50x);//停止摄相头工作和数据包送
- spcaCameraShutDown (spca50x);//关闭摄相头,由子函数spca50x_stop_iso完成
- for (i = 0; i < SPCA50X_NUMFRAMES; i++) //唤醒所有等待进程
- {
- if(waitqueue_active(&spca50x->frame[i].wq))
- wake_up_interruptible (&spca50x->frame[i].wq);
- }
- if(waitqueue_active (&spca50x->wq))
- wake_up_interruptible (&spca50x->wq);
- }
- up(&spca50x->lock);
- spca5xx_dealloc (spca50x);//回收内存空间
- PDEBUG(2,"Release ressources done");
- MOD_DEC_USE_COUNT;
- }
3、 Read功能
完成数据的读取,其主要的工作就是将数据由内核空间传送到进程用户空间
- static long spca5xx_rea(struct video_device *dev, char * buf, unsigned long count,int noblock)
- {
- struct usb_spca50x *spca50x = video_get_drvdata (dev);
- int i;
- int frmx = -1;
- int rc;
- volatile struct spca50x_frame *frame;
- if(down_interruptible(&spca50x->lock)) //获取信号量
- return -EINTR;
- if(!dev || !buf){//判断设备情况
- up(&spca50x->lock);
- return -EFAULT;
- }
- if(!spca50x->dev){
- up(&spca50x->lock);
- return -EIO;
- }
- if (!spca50x->streaming){
- up(&spca50x->lock);
- return -EIO;
- }
- if((rc = wait_event_interruptible(spca50x->wq, //在指定的队列上睡眠,直到参数2的条件为真
- spca50x->frame[0].grabstate == FRAME_DONE ||
- spca50x->frame[1].grabstate == FRAME_DONE ||
- spca50x->frame[2].grabstate == FRAME_DONE ||
- spca50x->frame[3].grabstate == FRAME_DONE )))
- {
- up(&spca50x->lock);
- return rc;
- }
- for (i = 0; i < SPCA50X_NUMFRAMES; i++) //当数据到来
- if (spca50x->frame[i].grabstate == FRAME_DONE) //标识数已到
- frmx = i;
- if (frmx < 0)
- {
- PDEBUG(2, "Couldnt find a frame ready to be read.");
- up(&spca50x->lock);
- return -EFAULT;
- }
- frame = &spca50x->frame[frmx];
- PDEBUG (2, "count asked: %d available: %d", (int) count,(int) frame->scanlength);
- if (count > frame->scanlength)
- count = frame->scanlength;
- if ((i = copy_to_user (buf, frame->data, count))) //实现用户空间和内核空间的数据贝
- {
- PDEBUG (2, "Copy failed! %d bytes not copied", i);
- up(&spca50x->lock);
- return -EFAULT;
- }
- /* Release the frame */
- frame->grabstate = FRAME_READY; //标识数据已空
- up(&spca50x->lock);
- return count;//返回拷贝的数据数
- }
4、Mmap功能
实现将设备内存映射到用户进程的地址空间的功能,其关键函数是remap_page_range,其具体实现如下:
- static int spca5xx_mmap(struct video_device *dev,const char *adr, unsigned long size)
- {
- unsigned long start = (unsigned long) adr;
- struct usb_spca50x *spca50x = dev->priv;
- unsigned long page, pos;
- if (spca50x->dev == NULL)
- return -EIO;
- PDEBUG (4, "mmap: %ld (%lX) bytes", size, size);
- if(size > (((SPCA50X_NUMFRAMES * MAX_DATA_SIZE) + PAGE_SIZE - 1) & ~(PAGE_SIZE -1)))
- return -EINVAL;
- if (down_interruptible(&spca50x->lock)) //获取信号量
- return -EINTR;
- pos = (unsigned long) spca50x->fbuf;
- while (size > 0) //循环实现内存映射
- {
- page = kvirt_to_pa (pos);
- if (remap_page_range (start, page, PAGE_SIZE, PAGE_SHARED)){ //实现内存映射
- up(&spca50x->lock);
- return -EAGAIN;
- }
- start += PAGE_SIZE;
- pos += PAGE_SIZE;
- if (size > PAGE_SIZE)
- size -= PAGE_SIZE;
- else
- size = 0;
- }
- up(&spca50x->lock); //释放信号量
- return 0;
- }
5、Ioctl功能:
实现文件信息的获取功能
- static int spca5xx_ioctl (struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg)
- {
- struct video_device *vdev = file->private_data;
- struct usb_spca50x *spca50x = vdev->priv;
- int rc;
- if(down_interruptible(&spca50x->lock)) //获取信号量
- return -EINTR;
- rc = video_usercopy (inode, file, cmd, arg, spca5xx_do_ioctl); //将信息传送到用户进程,其关键函数实现spca5xx_do_ioctl
- up(&spca50x->lock);
- return rc;
- }
spca5xx_do_ioctl函数的实现依赖于不同的硬件,本驱动为了支持多种芯片,实现程序过于烦琐,其主要思想是通过copy_to_user(arg,b,sizeof(struct video_capability)函数将设备信息传递给用户进程。
三、数据传输模块
源程序采用tasklet来实现同步快速传递数据,并通过spcadecode.c上的软件解码模块实现图形信息的解码。此模块的入口点挂节在spca_open函数中,其具体的函数为spca50x_init_isoc。当设备被打开时,同步传输数据也已经开始,并通过spca50x_move_data函数将数据传递给驱动程序,驱动程序通过轮询的办法实现对数据的访问。
- Void outpict_do_tasklet (unsigned long ptr)
- {
- int err;
- struct spca50x_frame *taskletframe = (struct spca50x_frame *) ptr;
- taskletframe->scanlength = taskletframe->highwater - taskletframe->data;
- PDEBUG (2, "Tasklet ask spcadecoder hdrwidth %d hdrheight %d method %d",
- taskletframe->hdrwidth, taskletframe->hdrheight,
- taskletframe->method);
- err = spca50x_outpicture (taskletframe); //输出处理过的图片数据
- if (err != 0)
- {
- PDEBUG (0, "frame decoder failed (%d)", err);
- taskletframe->grabstate = FRAME_ERROR;
- }
- else
- {
- taskletframe->grabstate = FRAME_DONE;
- }
- if (waitqueue_active (&taskletframe->wq))//如果有进程等待,唤醒等待进程
- wake_up_interruptible (&taskletframe->wq);
- }
值得一提的是spcadecode.c上解码模块将原始压缩图形数据流yyuyv,yuvy, jpeg411,jpeg422解码为RGB图形,但此部分解压缩算法的实现也依赖于压缩的格式,归根结底依赖于DSP(数字处理芯片)中的硬件压缩算法。
四.USB CORE的支持
LINUX下的USB设备对下层硬件的操作依靠系统实现的USB CORE层,USB CORE对上层驱动提供了众多函数接口如:usb_control_msg,usb_sndctrlpipe等,其中最典型的使用为源码中对USB端点寄存器的读写函数spca50x_reg_write和spca50x_reg_read等,具体实现如下:(举spca50x_reg_write的实现,其他类似)
- static int spca50x_reg_write(struct usb_device *dev,__u16 reg,__u16 index,__u16 value)
- {
- int rc;
- rc = usb_control_msg(dev, //通过USB CORE提供的接口函数设置寄存器的值
- usb_sndctrlpipe(dev, 0),
- reg,
- USB_TYPE_VENDOR | USB_RECIP_DEVICE,
- value, index, NULL, 0, TimeOut);
- PDEBUG(5, "reg write: 0x%02X,0x%02X:0x%02X, 0x%x", reg, index, value, rc);
- if (rc < 0)
- err("reg write: error %d", rc);
- return rc;
- }