help about dma

I have designed a software to implement the data transfer between the onchip memory and the SDRAM. during the debug, I fount that the dma only tranfer the last half data from the SDRAM to onchip memory, then creat the irq

to final the dma. I fell very confuse.

my code is below:

void dma_done (void* handle, void* data){

dma_complete = 1;

} /* dma_done */

int alt_main (void)

{

alt_dma_txchan tx;

if ( ( tx=alt_dma_txchan_open(DMA_0_NAME)) ==NULL)

{

return;

}

int res;

res=alt_dma_txchan_ioctl(tx, ALT_DMA_SET_MODE_32, NULL);

if(res){

return;

}

res=alt_dma_txchan_ioctl(tx,ALT_DMA_RX_STREAM_ON,(void *)buffer);

if(res){

return;

}

if(alt_dma_txchan_send(tx, (void *)SDRAM_BASE, 160, (alt_txchan_done *)dma_done, NULL)<0) http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/sad.gif

{

return;

}

while(!dma_complete);

alt_dma_txchan_close(tx);

dma_complete=0;

}

when the dma is final, the buffer only have 20 data, and these data is located in SDRAM_BASE+80;