AN2641 datasheet(24/37 Pages) STMICROELECTRONICS

24 / 37 page

Linux frame buffer

AN2641

24/37

Doc ID 14027 Rev 1

hold a pixel, pixclock, HSYNC duration, VSYNC duration, and margin lengths. These

values are programmable by the user:

Figure 12.

Structure fb_var_screeninfo

Fixed information about the video hardware, such as the start address and size of

frame buffer memory, is held in struct fb_fix_screeninfo. These values cannot be

altered by the user:

Figure 13.

Structure fb_fix_screeninfo

The fb_cmap structure specifies the color map, which is used to convey the user's

definition of colors to the underlying video hardware. You can use this structure to

define the RGB (Red, Green, and Blue) ratio that you desire for different colors: Device

independent color-map information. You can get and set the color-map using the

FBIOGETCMAP and FBIOPUTCMAP ioctls:

Figure 14.

Structure fb_cmap

struct fb_var_screeninfo {

__u32 xres; /* Visible resolution in the X axis */

__u32 yres; /* Visible resolution in the Y axis */

/* ... */

__u32 bits_per_pixel; /* Number of bits required to hold a pixel */

/* ... */

__u32 pixclock; /* Pixel clock in picoseconds */

__u32 left_margin; /* Time from sync to picture */

__u32 right_margin; /* Time from picture to sync */

/* ... */

__u32 hsync_len; /* Length of horizontal sync */

__u32 vsync_len; /* Length of vertical sync */

/* ... */

};

struct fb_fix_screeninfo {

char id[16]; /* Identification string */

unsigned long smem_start; /* Start of frame buffer memory */

__u32 smem_len; /* Length of frame buffer memory */

/* ... */

};

struct fb_cmap {

__u32 start; /* First entry */

__u32 len; /* Number of entries */

__u16 *red; /* Red values */

__u16 *green; /* Green values */

__u16 *blue; /* Blue values */

__u16 *transp; /* Transparency */

};

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