About DMA problem..please help me

I manage to get DMA transfer complete. but rewrite the code, and it only copy from a single address to buffer.(more like a streaming).

I read from the documentation that this method is supposed to be for peripheral to memory copy..however i give the input to it my 2nd SDRAM base address - which i name it mem_sdram (im using de2-70). So im assuming that it supposed to be copying only the first data to buffer which i declare earlier.

However after the transfer finish..i check the value inside buffer.Its not the same as in mem_sdram.

here is the output:

Testing DMA!
readaddress =4000000, length =0, status =0, control =1f9 
dma transfer: 1ms
Transaction complete 
0:3
1:0
2:0
3:0

it shows there '3' and followed by 0.Im expecting the buffer to be filled with '78'. because at the first 32bits of mem_sdram i have already write it with this command : iowr_32direct(mem_sdram_base,0,0x12345678);

Here is my code:

# define    DEPTH 4
# include <stdio.h># include <stddef.h># include <stdlib.h># include "string.h"# include "system.h"
# include "sys/alt_dma.h"# include "altera_avalon_dma_regs.h"# include "altera_avalon_dma.h"
# include "sys/alt_cache.h"# include "sys/alt_alarm.h"# include "alt_types.h"
volatile int dma_complete = 0;
void dma_done (void * handle, void * data)
{
    dma_complete = 1;
}
void check(void)
{
    alt_u32 control, status, readaddress, length;
    readaddress = IORD_ALTERA_AVALON_DMA_RADDRESS(DMA_BASE);
    printf ("readaddress =%x, ", readaddress);
    length = IORD_ALTERA_AVALON_DMA_LENGTH (DMA_BASE);
    printf ("length =%x, ", length);
    status = IORD_ALTERA_AVALON_DMA_STATUS (DMA_BASE);
    printf ("status =%x, ", status);
    control = IORD_ALTERA_AVALON_DMA_CONTROL (DMA_BASE);
    printf ("control =%x \n", control);
}
int main()
{
  printf("Testing DMA!\n");
  alt_u8 buffer;
  //memset(buffer, 0x55, 2024);
  alt_dcache_flush_all();
  alt_dma_rxchan_dev * rx;
  alt_u32 start,end;
  IOWR_32DIRECT(MEM_SDRAM_BASE,0,0x12345678);
  start = alt_nticks();
  if ((rx = alt_dma_rxchan_open ("/dev/dma")) == NULL)
  {
      printf ("Error: failed to open device");
      exit(1);
  }
  else
  {
     alt_dma_rxchan_ioctl(rx, ALT_DMA_SET_MODE_8, NULL);
     alt_dma_rxchan_ioctl(rx, ALT_DMA_TX_ONLY_OFF, NULL);
     alt_dma_rxchan_ioctl(rx, ALT_DMA_RX_ONLY_ON, (void *)MEM_SDRAM_BASE);
     check();
  }
  int ret;
  if ((ret = alt_dma_rxchan_prepare (rx,(void *) buffer, DEPTH , dma_done, NULL)) <0)
  {
      printf ("Error: failed to post receive request\n");
      exit (1);
  }
  while (!dma_complete);
  end = alt_nticks();
  printf("dma transfer: %dms\n",(end-start));
  /*start = alt_nticks();
  memcpy(buffer,(void *)MEM_SDRAM_BASE,DEPTH);
  end = alt_nticks();
  printf("memcpy transfer: %dms\n",(end-start));*/
  printf ("Transaction complete \n");
  alt_dma_rxchan_close(rx);
  for(int x=0;x<DEPTH;x++)
  {
      printf("%d:%x\n",x,buffer);
  }
  printf("---using IORD---\n");
  for(int x=0;x<DEPTH;x++)
  {
      printf("%d:%x\n",x,IORD_8DIRECT(MEM_SDRAM_BASE,0));
  }
  return 0;
}