页面树结构
转至元数据结尾
转至元数据起始

Framebuffer(帧缓冲)是Linux为显示设备提供的一个接口,把显存抽象后的一种设备,它允许上层应用程序在图形模式下直接对显示缓冲区进行读写操作。Framebuffer是LCD对应的一种件抽象层,提供抽象统一的操作接口,用户不必关心硬件层是如何实现。这些都是由Framebuffer设备驱动来完成的。

帧缓冲设备对应的设备文件为/dev/fb*,如果系统有多个显示卡,Linux下还可支持多个帧缓冲设备,最多可达32个,分别为/dev/fb0到 /dev/fb31,而/dev/fb则为当前缺省的帧缓冲设备,通常指向/dev/fb0,在嵌入式系统中支持一个显示设备就够了。帧缓冲设备为标准字符设备,主设备号为29,次设备号则从0到31。分别对应/dev/fb0-/dev/fb31。

linux/fd.h目录下定义了linux framebuffer的数据结构体。

struct fb_info {
	atomic_t count;
	int node;
	int flags;
	struct mutex lock;		/* Lock for open/release/ioctl funcs */
	struct mutex mm_lock;		/* Lock for fb_mmap and smem_* fields */
	struct fb_var_screeninfo var;	/* 当前可变的参数 */
	struct fb_fix_screeninfo fix;	/* 当前固定的参数 */
	struct fb_monspecs monspecs;	/* 描述当前显示器的特有固定信息*/
	struct work_struct queue;	/* Framebuffer event queue */
	struct fb_pixmap pixmap;	/* Image hardware mapper */
	struct fb_pixmap sprite;	/* Cursor hardware mapper */
	struct fb_cmap cmap;		/* 当前颜色映射表 */
	struct list_head modelist;      /* mode list */
	struct fb_videomode *mode;	/* current mode */

#ifdef CONFIG_FB_BACKLIGHT
	/* assigned backlight device */
	/* set before framebuffer registration, 
	   remove after unregister */
	struct backlight_device *bl_dev;

	/* Backlight level curve */
	struct mutex bl_curve_mutex;	
	u8 bl_curve[FB_BACKLIGHT_LEVELS];
#endif
#ifdef CONFIG_FB_DEFERRED_IO
	struct delayed_work deferred_work;
	struct fb_deferred_io *fbdefio;
#endif

	struct fb_ops *fbops;        /*指向当前显示器的特有固定的信息,可以通过ioctl()系统调用操作设备*/
	struct device *device;		/* This is the parent */
	struct device *dev;		/* This is this fb device */
	int class_flag;                    /* private sysfs flags */
#ifdef CONFIG_FB_TILEBLITTING
	struct fb_tile_ops *tileops;    /* Tile Blitting */
#endif
	char __iomem *screen_base;	/* Virtual address */
	unsigned long screen_size;	/* Amount of ioremapped VRAM or 0 */ 
	void *pseudo_palette;		/* Fake palette of 16 colors */ 
#define FBINFO_STATE_RUNNING	0
#define FBINFO_STATE_SUSPENDED	1
	u32 state;			/* Hardware state i.e suspend */
	void *fbcon_par;                /* fbcon use-only private area */
	/* From here on everything is device dependent */
	void *par;
	/* we need the PCI or similar aperture base/size not
	   smem_start/size as smem_start may just be an object
	   allocated inside the aperture so may not actually overlap */
	struct apertures_struct {
		unsigned int count;
		struct aperture {
			resource_size_t base;
			resource_size_t size;
		} ranges[0];
	} *apertures;
};


struct fb_fix_screeninfo 这个结构体用来描述设备无关,不可变更的信息。用户可以使用FBIOGET_FSCREENINFO命令来获得这些信息。

struct fb_fix_screeninfo {
	char id[16];			/* identification string eg "TT Builtin" */
	unsigned long smem_start;	/* 描述缓冲起始地址(物理地址) */
	__u32 smem_len;			/*描述缓冲区长度 */
	__u32 type;			/* 描述fb类型,比如TFT或STN类型*		*/
	__u32 type_aux;			/* Interleave for interleaved Planes */
	__u32 visual;			/*描述显示颜色是真彩色,伪彩色,还是单色 	*/ 
	__u16 xpanstep;			/* zero if no hardware panning  */
	__u16 ypanstep;			/* zero if no hardware panning  */
	__u16 ywrapstep;		/* zero if no hardware ywrap    */
	__u32 line_length;		/* length of a line in bytes    */
	unsigned long mmio_start;	/* I/O内存映射起始地址,物理地址 */
	__u32 mmio_len;			/* Length of Memory Mapped I/O  */
	__u32 accel;			/* Indicate to driver which	*/
					/*  specific chip/card we have	*/
	__u16 capabilities;		/* see FB_CAP_*			*/
	__u16 reserved[2];		/* Reserved for future compatibility */
};


struct fb_var_screeninfo该结构描述设备无关的,可以更改的配置信息。应用程序可以使用FBIOGET_VSCREENINFO命令来获得这些信息,使用FBIOPUT_VSCREENIFO命令写入这些信息

struct fb_var_screeninfo {
	__u32 xres;			/* visible resolution		*/
	__u32 yres;
	__u32 xres_virtual;		/* virtual resolution		*/
	__u32 yres_virtual;
	__u32 xoffset;			/* offset from virtual to visible */
	__u32 yoffset;			/* resolution			*/

	__u32 bits_per_pixel;		/* guess what			*/
	__u32 grayscale;		/* 0 = color, 1 = grayscale,	*/
					/* >1 = FOURCC			*/
	struct fb_bitfield red;		/* bitfield in fb mem if true color, */
	struct fb_bitfield green;	/* else only length is significant */
	struct fb_bitfield blue;
	struct fb_bitfield transp;	/* transparency			*/	

	__u32 nonstd;			/* != 0 Non standard pixel format */

	__u32 activate;			/* see FB_ACTIVATE_*		*/

	__u32 height;			/* height of picture in mm    */
	__u32 width;			/* width of picture in mm     */

	__u32 accel_flags;		/* (OBSOLETE) see fb_info.flags */

	/* Timing: All values in pixclocks, except pixclock (of course) */
	__u32 pixclock;			/* pixel clock in ps (pico seconds) */
	__u32 left_margin;		/* time from sync to picture	*/
	__u32 right_margin;		/* time from picture to sync	*/
	__u32 upper_margin;		/* time from sync to picture	*/
	__u32 lower_margin;
	__u32 hsync_len;		/* length of horizontal sync	*/
	__u32 vsync_len;		/* length of vertical sync	*/
	__u32 sync;			/* see FB_SYNC_*		*/
	__u32 vmode;			/* see FB_VMODE_*		*/
	__u32 rotate;			/* angle we rotate counter clockwise */
	__u32 colorspace;		/* colorspace for FOURCC-based modes */
	__u32 reserved[4];		/* Reserved for future compatibility */
};
  • 无标签
编写评论...