how to write fb?

This is an example showing how to verify the functionality of a embedded system fb. To compile the below code, this is the command.

"$CROSS_COMPILE"gcc fbapp.c -o fbapp

#include ...

#define ERROR(x) printf("fbtest error in line %s:%d: %s\n", __FUNCTION__, __LINE__, strerror(errno));

#define FBCTL(cmd, arg) \
if(ioctl(fd, cmd, arg) == -1) { \
ERROR("ioctl failed"); \
exit(1); }

#define FBCTL0(cmd) \
if(ioctl(fd, cmd) == -1) { \
ERROR("ioctl failed"); \
exit(1); }

struct fb_var_screeninfo var;
struct fb_fix_screeninfo fix;

int open_fb(const char* dev)
{
int fd = -1;
fd = open(dev, O_RDWR);
if(fd == -1)
{
printf("Error opening device %s : %s\n", dev, strerror(errno));
exit(-1);
}

return fd;
}

static void draw_pixel(void *fbmem, int x, int y, unsigned color)
{
if (var.bits_per_pixel == 16) {
unsigned short c;
unsigned r = (color >> 16) & 0xff;
unsigned g = (color >> 8) & 0xff;
unsigned b = (color >> 0) & 0xff;
unsigned short *p;

r = r * 32 / 256;
g = g * 64 / 256;
b = b * 32 / 256;

c = (r << 11) | (g << 5) | (b << 0);

fbmem += fix.line_length * y;

p = fbmem;

p += x;

*p = c;
} else {
unsigned int *p;

fbmem += fix.line_length * y;

p = fbmem;

p += x;

*p = color;
}
}

void fill_screen(void *fbmem)
{
unsigned x, y;
unsigned h = var.yres; //yres_virtual;
unsigned w = var.xres; //xres_virtual;
  // int color;
  for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
  draw_pixel(fbmem, x, y, (y? 0x00FFFFFF:0));}
        }
}
}
}

int main(int argc, char** argv)
{
int fb_num;
char str[64];
int fd;

if (argc == 2)
fb_num = atoi(argv[1]);
else
fb_num = 0;

sprintf(str, "/dev/graphics/fb%d", fb_num);
printf("opening %s\n", str);

fd = open(str, O_RDWR);

FBCTL(FBIOGET_VSCREENINFO, &var);
FBCTL(FBIOGET_FSCREENINFO, &fix);

printf("res %d,%d virtual %d,%d, line_len %d, bits_per_pixel %d\n",
var.xres, var.yres,
var.xres_virtual, var.yres_virtual,
fix.line_length,
var.bits_per_pixel);

void* ptr = mmap(0, var.yres_virtual * fix.line_length,
PROT_WRITE | PROT_READ,
MAP_SHARED, fd, 0);

if(ptr == MAP_FAILED) {
perror("mmap failed");
exit(1);
}

fill_screen(ptr);
return 0;
}

how-to setup busy box ?

The busybox could be cross compiled for arm-none-linux-gnueabi-gcc.
It is cross compiled with static link option.
make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi-
User could cp the busybox to /system/bin of the target sd card.

//install manually
adb shell
su
mount -o rw,remount -t yaffs2 /dev/block/mtdblock3 /system
exit
adb push busybox /data/local
adb shell
cd /system
ls -al


cd /data/local
chmod busybox 755
/data/local/busybox cp /data/local/busybox /system/xbin/busybox
cd /system/xbin
chmod busybox 755
./busybox --install -s /system/xbin
rm /data/local/busybox