Error -In dma data transfer

hello i am newbie ,please help me.

i have following error.

i am using four task for displaying leds and i am using button as an interrupt,so when i press any switch button it will go to interrupt service routine ,so from there in interupt service routine i am making dma data transfer.But i have problem here- in interrupt service routine dma transfer is not working/or may be it is hanged somhow in interrupt service routine.I do not know why?

but if i will use dma function once before the Interrupt service routine comes then i am able to use DMA in interrupt service routine. this time there is not blocking/hanging why?i do not know please help me .

I am using full-featured cyclone-EP1c20 with nios 2.

# include <stdio.h># include "board_diag.h"# include "alt_types.h"# include <unistd.h># include "system.h"# include "sys/alt_irq.h"# include "altera_avalon_pio_regs.h"# include <stdlib.h># include "sys/alt_dma.h"

alt_u8 led,q;

volatile int edge_capture;

static volatile int rx_done = 0;

/* Callback function that obtains notification that the data has

* been received.

*/

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

{

rx_done++;

}

int dma ()

{

int rc;

alt_dma_txchan txchan;

alt_dma_rxchan rxchan;

alt_u32 length=32;

void* tx_data = (void*) 0x2000010; /* pointer to data to send */

void* rx_buffer = (void*) 0x2010000; /* pointer to rx buffer */

/* Create the transmit channel */

if ((txchan = alt_dma_txchan_open("/dev/dma")) == NULL)

{

led = 0x07;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(4000000);

exit (1);

}

/* Create the receive channel */

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

{

led = 0x0f;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(4000000);

exit (1);

}

/* Post the transmit request */

if ((rc = alt_dma_txchan_send (txchan,

tx_data,

length,

NULL,

NULL)) < 0)

{

led = 0x1f;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(4000000);

exit (1);

}

/* Post the receive request */

if ((rc = alt_dma_rxchan_prepare (rxchan,rx_buffer,length,done,NULL)) < 0)

{

led = 0x3f;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(4000000);

exit (1);

}

/* wait for transfer to complete */

while (!rx_done);

led = 0x40;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(4000000);

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

return 0;

}

static void Task1(void)

{

led = 0x1;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(2000000);

}

static void Task2(void)

{

led = 0x2;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(2000000);

}

static void Task3(void)

{

led = 0x4;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(2000000);

}

static void Task4(void)

{

led = 0x8;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(2000000);

}

# ifdef BUTTON_PIO_BASE

static void handle_button_interrupts(void* context, alt_u32 id)

{

/* Cast context to edge_capture&#39;s type. It is important that this be

* declared volatile to avoid unwanted compiler optimization.

*/

volatile int* edge_capture_ptr = (volatile int*) context;

/* Store the value in the Button&#39;s edge capture register in *context. */

*edge_capture_ptr = IORD_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE);

led = 0x20;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);

usleep(2000000);

/* Reset the Button&#39;s edge capture register. */

IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0);

/*call for dma transfer*/;

q=dma();

}

/* Initialize the button_pio. */

static void init_button_pio()

{

/* Recast the edge_capture pointer to match the alt_irq_register() function

* prototype. */

void* edge_capture_ptr = (void*) &edge_capture;

/* Enable all 4 button interrupts. */

IOWR_ALTERA_AVALON_PIO_IRQ_MASK(BUTTON_PIO_BASE, 0xf);

/* Reset the edge capture register. */

IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0x0);

/* Register the interrupt handler. */

alt_irq_register( BUTTON_PIO_IRQ, edge_capture_ptr, handle_button_interrupts );

}# endif

int main()

{

/* Initialize the button pio. */

int q;# ifdef BUTTON_PIO_BASE

init_button_pio();# endif

q=dma();

while(1)

{

Task1();

Task2();

Task3();

Task4();

}

return(0);

}