error-In dma -data transfer

[Altera_Forum]

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); }