[임베디드 리눅스] Frame Buffer (프레임 버퍼) 다루기

[임베디드 리눅스] Frame Buffer (프레임 버퍼) 다루기

1. 소스 코드

// GUI_Main.c #include <stdio.h> //sprintf #include <stdlib.h> //atio #include "GUI_FrameBuffer.h" int main(int argc, char** argv) { int fb_num; char fb_path[32]; if (argc >= 2) { fb_num = atoi(argv[1]); sprintf(fb_path, "/dev/fb%d", fb_num); } else { sprintf(fb_path, "/dev/fb"); } GUI_FB_Open(fb_path); GUI_FB_Close(); return 0; } // GUI_FrameBuffer.h #ifndef __GUI_FRAMEBUFFER_H__ #define __GUI_FRAMEBUFFER_H__ #pragma pack(1) /////////////////////////////////////////////////////////////////////// // define /////////////////////////////////////////////////////////////////////// typedef struct _GUI_FB { int screen_width; int screen_height; int bits_per_pixel; int line_length; int fd; void *fb_mem; int mem_size; unsigned int red_offset; unsigned int green_offset; unsigned int blue_offset; } GUI_FB_t; /////////////////////////////////////////////////////////////////////// // external variable /////////////////////////////////////////////////////////////////////// extern GUI_FB_t *g_fb; // frame buff /////////////////////////////////////////////////////////////////////// // external function /////////////////////////////////////////////////////////////////////// extern int GUI_FB_Open(const char *fb_path); extern int GUI_FB_Close(void); #endif // GUI_FrameBuffer.c #include <stdio.h> //printf #include <stdlib.h> //malloc #include <unistd.h> //open,close #include <fcntl.h> //O_RDWR #include <sys/ioctl.h> //ioctl #include <sys/mman.h> //mmap,PROT_ #include <linux/fb.h> //fb_var_screeninfo,fb_fix_screeninfo #include "GUI_Type.h" #include "GUI_FrameBuffer.h" /////////////////////////////////////////////////////////////////////// // external variable /////////////////////////////////////////////////////////////////////// GUI_FB_t *g_fb; // frame buff /////////////////////////////////////////////////////////////////////// // external function /////////////////////////////////////////////////////////////////////// int GUI_FB_Open(const char *fb_path) { struct fb_var_screeninfo var; // variable information of frame struct fb_fix_screeninfo fix; // fixed information of frame g_fb = (GUI_FB_t *)malloc(sizeof(GUI_FB_t)); // access if ( access( fb_path, F_OK ) ) { printf("Can't access %s\n", fb_path); return 0; } // open if ( 0 > (g_fb->fd = open( fb_path, O_RDWR )) ) { printf("%s permission denied\n", fb_path); return 0; } // io control var info if ( ioctl( g_fb->fd, FBIOGET_VSCREENINFO, &var) ) { printf("can't execute FBIOGET_VSCREENINFO\n"); return 0; } // io control fix info if ( ioctl( g_fb->fd, FBIOGET_FSCREENINFO, &fix) ) { printf("can't execute FBIOGET_FSCREENINFO\n"); return 0; } g_fb->screen_width = var.xres; // screen width pixel g_fb->screen_height = var.yres; // screen height pixel g_fb->bits_per_pixel = var.bits_per_pixel; // bits per pixel g_fb->line_length = fix.line_length; // bytes per line g_fb->mem_size = g_fb->line_length * g_fb->screen_height; // memory size g_fb->red_offset = var.red.offset; // red offset g_fb->green_offset = var.green.offset; // green offset g_fb->blue_offset = var.blue.offset; // blue offset #if 1 printf( "*********************************************************\n"); printf( "** FRAME BUFFER INFO **\n"); printf( "*********************************************************\n"); printf( "frame buff open (%s)\n", fb_path); printf( "screen width = %d\n", g_fb->screen_width ); printf( "screen height = %d\n", g_fb->screen_height ); printf( "bits per pixel = %d\n", g_fb->bits_per_pixel); printf( "line length = %d\n", g_fb->line_length ); printf( "memory size = %d\n", g_fb->mem_size ); #endif return 1; } int GUI_FB_Close(void) { if (g_fb == NULL) { return 0; } free(g_fb); g_fb = NULL; return 1; }

2. 실행 결과

# /mnt/mmc# ./fb_test
Can't access /dev/fb

# /mnt/mmc# ./fb_test 0
*********************************************************
** FRAME BUFFER INFO                                   **
*********************************************************
frame buff open (/dev/fb0)
screen width   = 240
screen height  = 320
bits per pixel = 32
line length    = 960
memory size    = 307200

# /mnt/mmc# ./fb_test 1
*********************************************************
** FRAME BUFFER INFO                                   **
*********************************************************
frame buff open (/dev/fb1)
screen width   = 320
screen height  = 240
bits per pixel = 32
line length    = 1280
memory size    = 307200

3. 설명

프레임 버퍼란 LCD 디바이스의 입출력 데이터를 저장 및 송수신하는 구간으로 /dev/fb 파일의 읽고 쓰기로 제어가 가능하다.

사진 출처 : http://www.slideshare.net/chon2010/ss-5653835

[Reference]

(access 함수) http://forum.falinux.com/zbxe/index.php?document_srl=412987&mid=C_LIB

(ioctl 함수) http://damduc.tistory.com/216

(frame buffer 이야기) http://elechole.tistory.com/237

(The Frame Buffer Device API) https://www.kernel.org/doc/Documentation/fb/api.txt