descriptor_allocation.c

DMA exmaple,网路上找到的DMA程式范例

#include "stdio.h"
#include "stdlib.h"
#include "io.h"
#include "alt_types.h"
#include "altera_avalon_sgdma_descriptor.h"


/**********************************************************************************
 * This function is called with double pointers so that it can modify (allocate)  *
 * the regions in memory to be pointed at. The easiest way to call this function  *
 * is to pass in single pointers by reference (thereby creating double pointers). *
 *                                                                                *
 * Since the descriptor masters are 256 bits wide (32 bytes) we must ensure that  *
 * all descriptors are located on 32 byte boundaries. This function will allocate *
 * enough space for one additional descriptor and slide the pointer from the      *
 * beginning until it is on a 32 byte boundary. Malloc can only provide 8 byte    *
 * alignment so without a custom memory allocation library this step is necessary *
 *                                                                                *
 * Returns 0 for sucess, 1 for failure.                                           *
 **********************************************************************************/
alt_u32 descriptor_allocation(alt_sgdma_descriptor ** transmit_descriptors,
                      alt_sgdma_descriptor ** transmit_descriptors_copy,
                      alt_sgdma_descriptor ** receive_descriptors,
                      alt_sgdma_descriptor ** receive_descriptors_copy,
                      alt_u32 number_of_buffers)
{
  /* Allocate some big buffers to hold all descriptors which will slide until
   * the first 32 byte boundary is found */
  void * temp_ptr_1, * temp_ptr_2;


/**************************************************************
   * Allocation of the transmit descriptors                   *
   * - First allocate a large buffer to the temporary pointer *
   * - Second check for sucessful memory allocation           *
   * - Third put this memory location into the pointer copy   *
   *   to be freed before the program exits                   *
   * - Forth slide the tempory pointer until it lies on a 32  *
   *   byte boundary (descriptor master is 256 bits wide)     * 
   ************************************************************/  
  temp_ptr_1 = malloc((number_of_buffers + 2) * ALTERA_AVALON_SGDMA_DESCRIPTOR_SIZE);
  if(temp_ptr_1 == NULL)
  {
    printf("Failed to allocate memory for the transmit descriptors\n");
    return 1; 
  }
  *transmit_descriptors_copy = (alt_sgdma_descriptor *)temp_ptr_1;
  
  while((((alt_u32)temp_ptr_1) % ALTERA_AVALON_SGDMA_DESCRIPTOR_SIZE) != 0)
  {
    temp_ptr_1++;  // slide the pointer until 32 byte boundary is found
  }
  *transmit_descriptors = (alt_sgdma_descriptor *)temp_ptr_1;
/**************************************************************/


/**************************************************************
   * Allocation of the receive descriptors                    *
   * - First allocate a large buffer to the temporary pointer *
   * - Second check for sucessful memory allocation           *
   * - Third put this memory location into the pointer copy   *
   *   to be freed before the program exits                   *
   * - Forth slide the tempory pointer until it lies on a 32  *
   *   byte boundary (descriptor master is 256 bits wide)     * 
   ************************************************************/  
  temp_ptr_2 = malloc((number_of_buffers + 2) * ALTERA_AVALON_SGDMA_DESCRIPTOR_SIZE);
  if(temp_ptr_2 == NULL)
  {
    printf("Failed to allocate memory for the receive descriptors\n");
    return 1; 
  }
  *receive_descriptors_copy = (alt_sgdma_descriptor *)temp_ptr_2;
  
  while((((alt_u32)temp_ptr_2) % ALTERA_AVALON_SGDMA_DESCRIPTOR_SIZE) != 0)
  {
    temp_ptr_2++;  // slide the pointer until 32 byte boundary is found
  }
  *receive_descriptors = (alt_sgdma_descriptor *)temp_ptr_2;
/**************************************************************/

  return 0;  // no failures in allocation
}

/******************************************************************************
*                                                                             *
* License Agreement                                                           *
*                                                                             *
* Copyright (c) 2007 Altera Corporation, San Jose, California, USA.           *
* All rights reserved.                                                        *
*                                                                             *
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*                                                                             *
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*                                                                             *
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*                                                                             *
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******************************************************************************/