分类: 嵌入式
2011-05-03 08:58:40
因为Linux是工作在保护模式下,所以用户态进程是无法象DOS那样使用显卡BIOS里
提供的中断调用来实现直接写屏,故Linux抽象出FrameBuffer这个设备来供用户态
进程实现直接写屏。
在继续下面的之前,先说明几个背景知识:
1、FrameBuffer主要是根据VESA标准的实现的,所以只能实现最简单的功能。
2、由于涉及内核的问题,FrameBuffer是不允许在系统起来后修改显示模式等一系
列操作。(好象很多人都想要这样干,这是不被允许的,当然如果你自己与驱动
的话,是可以实现的)
3、对FrameBuffer的操作,会直接影响到本机的所有控制台的输出,包括XWIN的图
形界面。
好,现在可以让我们开始实现直接写屏:
1、打开一个FrameBuffer设备
2、通过mmap调用把显卡的物理内存空间映射到用户空间
3、直接写内存。
好象很简单哦~
fbtools.h
#ifndef _FBTOOLS_H_
#define _FBTOOLS_H_
#include
<linux/fb.h>
//a framebuffer device structure;
typedef struct fbdev{
int fb;
unsigned long fb_mem_offset;
unsigned long fb_mem;
struct fb_fix_screeninfo fb_fix;
struct fb_var_screeninfo fb_var;
char dev[20];
} FBDEV, *PFBDEV;
//open & init a frame buffer
//to use this function,
//you must set FBDEV.dev="/dev/fb0"
//or "/dev/fbX"
//it's your frame buffer.
int fb_open(PFBDEV pFbdev);
//close a frame buffer
int fb_close(PFBDEV pFbdev);
//get display depth
int get_display_depth(PFBDEV pFbdev);
//full screen clear
void fb_memset(void *addr, int c, size_t len);
#endif
fbtools.c
#include
#include
#include
#include
#include
#include
#include
#include
#include "fbtools.h"
#define TRUE
1
#define FALSE
0
#define MAX(x,y)
((x)>(y)?(x):(y))
#define MIN(x,y)
((x)<(y)?(x):(y))
//open & init a frame buffer
int fb_open(PFBDEV pFbdev)
{
pFbdev->fb =
open(pFbdev->dev, O_RDWR);
if(pFbdev->fb
< 0)
{
printf("Error opening %s: %m.
Check kernel config\n", pFbdev->dev);
return FALSE;
}
if (-1 ==
ioctl(pFbdev->fb,FBIOGET_VSCREENINFO,&(pFbdev->fb_var)))
{
printf("ioctl
FBIOGET_VSCREENINFO\n");
return FALSE;
}
if (-1 ==
ioctl(pFbdev->fb,FBIOGET_FSCREENINFO,&(pFbdev->fb_fix)))
{
printf("ioctl
FBIOGET_FSCREENINFO\n");
return FALSE;
}
//map physics address to virtual address
pFbdev->fb_mem_offset = (unsigned
long)(pFbdev->fb_fix.smem_start) &
(~PAGE_MASK);
pFbdev->fb_mem = (unsigned long
int)mmap(NULL, pFbdev->fb_fix.smem_len +
pFbdev->fb_mem_offset,
PROT_READ | PROT_WRITE,
MAP_SHARED, pFbdev->fb, 0);
if (-1L == (long)
pFbdev->fb_mem)
{
printf("mmap error! mem:%d
offset:%d\n", pFbdev->fb_mem,
pFbdev->fb_mem_offset);
return FALSE;
}
return TRUE;
}
//close frame buffer
int fb_close(PFBDEV pFbdev)
{
close(pFbdev->fb);
pFbdev->fb=-1;
}
//get display depth
int get_display_depth(PFBDEV pFbdev);
{
if(pFbdev->fb<=0)
{
printf("fb device not
open, open it first\n");
return FALSE;
}
return
pFbdev->fb_var.bits_per_pixel;
}
//full screen clear
void fb_memset (void *addr, int c, size_t len)
{
memset(addr, c, len);
}
//use by test
#define DEBUG
#ifdef DEBUG
main()
{
FBDEV fbdev;
memset(&fbdev, 0,
sizeof(FBDEV));
strcpy(fbdev.dev, "/dev/fb0");
if(fb_open(&fbdev)==FALSE)
{
printf("open frame buffer
error\n");
return;
}
fb_memset(fbdev.fb_mem + fbdev.fb_mem_offset, 0,
fbdev.fb_fix.smem_len);
fb_close(&fbdev);
}