alt_avalon_sgdma_construct_mem_to_mem_desc()

how to created all the descriptors?is the following code right?

///////////////////////////////////////////////////////////////////

alt_u32 *write_addr_1 = (alt_u32 *)(DDR_SDRAM_BASE);

alt_u32 *write_addr_2 = (alt_u32 *)(DDR_SDRAM_BASE+0xDFFC);

alt_avalon_sgdma_construct_mem_to_mem_desc(

&desc[0],

&desc[1],

read_addr,

write_addr_1,

65530,

1,

0);

alt_avalon_sgdma_construct_mem_to_mem_desc(

&desc[2],

&desc[3],

read_addr,

write_addr_2,

65530,

1,

0);

alt_avalon_sgdma_do_sync_transfer(sgdma_sdram, &desc[0]);

//////////////////////////////////////////////////////////////////

I have try both the DMA and sgdma, but I can only transmit the limited number of data(cannot use "for-loop" to translate larger data ), maybe I overlook configurating some registers or someting,I have read manualbook several times,and fanally failed,is there some advise for me,thanks~