de2-115-fpga-pong/software/Pong_Code_bsp/HAL/src/alt_read.c

/******************************************************************************
*                                                                             *
* License Agreement                                                           *
*                                                                             *
* Copyright (c) 2006 Altera Corporation, San Jose, California, USA.           *
* All rights reserved.                                                        *
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******************************************************************************/

#include <unistd.h>
#include <fcntl.h>

#include "sys/alt_errno.h"
#include "sys/alt_warning.h"
#include "priv/alt_file.h"
#include "os/alt_syscall.h"

/*
 * The read() system call is used to read a block of data from a file or device.
 * This function simply vectors the request to the device driver associated
 * with the input file descriptor "file". 
 *
 * ALT_READ is mapped onto the read() system call in alt_syscall.h
 */

#ifdef ALT_USE_DIRECT_DRIVERS

#include "system.h"
#include "sys/alt_driver.h"

/*
 * Provide minimal version that just reads from the stdin device when provided.
 */

int ALT_READ (int file, void *ptr, size_t len)
{
#ifdef ALT_STDIN_PRESENT
    ALT_DRIVER_READ_EXTERNS(ALT_STDIN_DEV);
#endif

#if !defined(ALT_STDIN_PRESENT)
    /* Generate a link time warning, should this function ever be called. */
    ALT_STUB_WARNING(read);
#endif

    switch (file) {
#ifdef ALT_STDIN_PRESENT
    case 0: /* stdin file descriptor */
        return ALT_DRIVER_READ(ALT_STDIN_DEV, ptr, len, 0);
#endif /* ALT_STDIN_PRESENT */
    default:
        ALT_ERRNO = EBADFD;
        return -1;
    }
}

#else /* !ALT_USE_DIRECT_DRIVERS */

int ALT_READ (int file, void *ptr, size_t len)
{
  alt_fd*  fd;
  int      rval;

  /*
   * A common error case is that when the file descriptor was created, the call
   * to open() failed resulting in a negative file descriptor. This is trapped
   * below so that we don't try and process an invalid file descriptor.
   */

  fd = (file < 0) ? NULL : &alt_fd_list[file];
  
  if (fd)
  {
    /*
     * If the file has not been opened with read access, or if the driver does
     * not provide an implementation of read(), generate an error. Otherwise
     * call the drivers read() function to process the request.
     */

    if (((fd->fd_flags & O_ACCMODE) != O_WRONLY) && 
        (fd->dev->read))
      {
        if ((rval = fd->dev->read(fd, ptr, len)) < 0)
        {
          ALT_ERRNO = -rval;
          return -1;
        }
        return rval;
      }
      else
      {
        ALT_ERRNO = EACCES;
      }
    }
  else
  {
    ALT_ERRNO = EBADFD;
  }
  return -1;
}

#endif /* ALT_USE_DIRECT_DRIVERS */