URGENT: Peripheral to Memory DMA Transaction

I tried out some code from this forum. I cannot write the result from peripheral to SDRAM. my code is as follow:

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# include "io.h"# include <stdio.h># include <unistd.h># include <sys/alt_dma.h># include "altera_avalon_pio_regs.h"# include "alt_types.h"# include "system.h"# include "sys/alt_timestamp.h"

# ifndef datax

# define datax 0x0# endif# ifndef datay

# define datay 0x1# endif# ifndef datau

# define datau 0x2# endif

/*

unsigned long add_h(unsigned long a, unsigned long b);

unsigned long add_h(unsigned long a, unsigned long b)

{

long result;

IOWR(AVALON_0_BASE,datax,a);

IOWR(AVALON_0_BASE,datay,b);

result = IORD(AVALON_0_BASE,datau);

return result;

}

*/

static volatile int rx_done = 0;

static void transfer_done (void* handle, void* data)

{

rx_done++;

}

void mem2mem_DMA(unsigned int dst, int length, unsigned long a, unsigned long b)

{

void *rx_data = (void *) dst;

alt_dma_rxchan rxchan;

int ret_code;

IOWR(AVALON_0_BASE,datax,a); // Data x

IOWR(AVALON_0_BASE,datay,b); // Data y

/* Create the receive channel */

if ((rxchan = alt_dma_rxchan_open("/dev/dma")) == NULL)

{

printf("Failed to open receive channel\n");

exit (1);

}

ret_code = alt_dma_rxchan_ioctl(rxchan, ALT_DMA_SET_MODE_32, NULL);

if (ret_code)

{

printf("Error: SET_MODE_32: %d.\n", ret_code);

exit(1);

}

ret_code = alt_dma_rxchan_ioctl(rxchan, ALT_DMA_RX_ONLY_ON, (void*)(AVALON_0_BASE));

if (ret_code)

{

printf("Error: ALT_DMA_RX_STREAM_ON: %d.\n", ret_code);

exit(1);

}

/* Post the receive request */

if ((ret_code = alt_dma_rxchan_prepare(rxchan, rx_data, length, transfer_done, NULL)) < 0)

{

printf("Failed to post read request, reason = %i\n", ret_code);

exit (1);

}

/* wait for transfer to complete */

while (!rx_done);

printf("Transfer successful!\n\n");

}

int main(void)

{

printf("\nThis is 32bits addition operation \n\n");

unsigned int dst = SDRAM_BASE + 0x600000;

unsigned long number[100];

//unsigned long output1[100];

int i=0;

int w;

printf("Please specify number of sets of random number:\t ");

scanf("%d", &w);

for (i=0;i<w;i++)

{

number= 300000000;

mem2mem_dma(dst, w, number, number);

}

for(i=0; i<w; i++)

{

printf("%ld\t %ld\n",number, IORD(dst, i));

}

return 0;

}

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My peripheral address is AVALON_0_BASE. This peripheral will add up 2 number, x and y. In this case, I set both x and y to be number[i], that is 300000000. Please assist. Thanks! really headache dealing with DMA.