Cannot write on-chip memory with fread.

I use DE2-70 to develop my project. My uClinux is running in SDRAM, and I want to copy a file to on-chip memory, but there is only 0 in on-chip memory, the fread() function didn't work.

can anyone help me in removing this error,

Thanks a lot !

Code:

int main()

{

FILE *fp1;

unsigned int *mem_source = (unsigned int *)(na_onchip_mem_source|0x80000000);

fp1 = open_file("P.dat",READ);

long length;

fseek(fp1, 0L, SEEK_END);

length = ftell(fp1);

int counter = 0;

fseek(fp1,0L,SEEK_SET);

fread(mem_source,length,1,fp1);

int i;

for(i=0;i<(length+3)/4;i++)

printf("mem_source %d = %x\n",i,mem_source[i]);

return 0;

}