showems.c

原创于 2007-11-08 21:36:00 发布 · 464 阅读

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#struct #attributes #dos #fp #character #include

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本文介绍了一个利用EMS内存的示例程序，演示了如何检查EMS驱动是否安装、分配EMS内存、映射物理页面到逻辑页面，并展示了如何通过改变映射来更新页面内容。

name="google_ads_frame" marginwidth="0" marginheight="0" src="http://pagead2.googlesyndication.com/pagead/ads?client=ca-pub-5572165936844014&dt=1194442938015&lmt=1194190197&format=336x280_as&output=html&correlator=1194442937843&url=file%3A%2F%2F%2FC%3A%2FDocuments%2520and%2520Settings%2Flhh1%2F%E6%A1%8C%E9%9D%A2%2FCLanguage.htm&color_bg=FFFFFF&color_text=000000&color_link=000000&color_url=FFFFFF&color_border=FFFFFF&ad_type=text&ga_vid=583001034.1194442938&ga_sid=1194442938&ga_hid=1942779085&flash=9&u_h=768&u_w=1024&u_ah=740&u_aw=1024&u_cd=32&u_tz=480&u_java=true" frameborder="0" width="336" scrolling="no" height="280" allowtransparency="allowtransparency"> #include <stdio.h>
#include <stdlib.h>
#include <dos.h>
#include <string.h>

int check_for_ems(void)
{
     union REGS inregs, outregs;
     struct SREGS segs;

     int major, minor;   // DOS version

     struct DeviceHeader
   {
       struct DeviceHeader far *link;
       unsigned attributes;
       unsigned strategy_offset;
       unsigned interrupt_offset;
       char name_or_number_of_units[8];
     } far *dev;

int i;
char driver_name[9];

     // Get the DOS version
     inregs.x.ax = 0x3001;
     intdos (&inregs, &outregs);
     major = outregs.h.al;
     minor = outregs.h.ah;

     if (major < 2)
       return(0);     // Requires DOS 2.0
     else
       {
   // Get the list of lists
   inregs.h.ah = 0x52;
   intdosx (&inregs, &outregs, &segs);

   if (major == 2)
    dev = (struct DeviceHeader far *)
     MK_FP(segs.es + 1, outregs.x.bx + 7);
   else if ((major == 3) && (minor == 0))
    dev = (struct DeviceHeader far *)
     MK_FP(segs.es + 2, outregs.x.bx + 8);
   else
    dev = (struct DeviceHeader far *)
     MK_FP(segs.es + 2, outregs.x.bx + 2);

   while (FP_OFF(dev) != 0xFFFF)
    {
     if (dev->attributes & 0x8000)
   { // Character device
    for (i = 0; i < 8; i++)
     driver_name[i] = dev->name_or_number_of_units[i];
    driver_name[8] = NULL;
   }

     if (! strcmp(driver_name, "EMMXXXX0"))
   return(1);   // Found driver

     dev = dev->link;
    }
     }

return(0);
}

void main(void)
{
union REGS inregs, outregs;
struct SREGS segs;

    unsigned handle;
    unsigned page;
    unsigned index, page_number;

unsigned page_frame_address;

char far *data;

if (check_for_ems())
{
inregs.h.ah = 0x40;
int86 (0x67, &inregs, &outregs);

// Make sure EMS is functional
if (outregs.h.ah == 0)
   {
     // Allocate a handle for 5 pages
     inregs.h.ah = 0x43;
     inregs.x.bx = 5;
     int86 (0x67, &inregs, &outregs);

     if (outregs.h.ah == 0)
       {
   handle = outregs.x.dx;

   // Get the page frame address
   inregs.h.ah = 0x41;
   int86 (0x67, &inregs, &outregs);

   if (outregs.h.ah == 0)
     {
       page_frame_address = outregs.x.bx;

       // map the first 4 pages
       for (page_number = 0; page_number < 4; page_number++)
         {
     inregs.h.ah = 0x44;
     inregs.h.al = page_number; // Physical page
     inregs.x.bx = page_number; // Logical page
     inregs.x.dx = handle;

     int86 (0x67, &inregs, &outregs);

     if (outregs.h.ah != 0)
       {
          printf ("Error mapping pages %xH/n",
     outregs.h.ah);

          // Release the handle
          inregs.h.ah = 0x45;
          inregs.x.dx = handle;
          int86 (0x67, &inregs, &outregs);
          exit(0);
       }
         }
       // Fill the first four pages
       data = (char far *) MK_FP(page_frame_address, 0);

       for (index = 0; index < 16384; index++)
         data[index] = 'A';

for (index = 16384; index < 32768; index++)
data[index] = 'B';

for (index = 32768; index < 49152; index++)
data[index] = 'C';

for (index = 49152; index != 0; index++)
data[index] = 'D';

       // Map logical page 4 into physical page 1
       inregs.h.ah = 0x44;
       inregs.h.al = 1; // Physical page
       inregs.x.bx = 4; // Logical page
       inregs.x.dx = handle;

       int86 (0x67, &inregs, &outregs);

       if (outregs.h.ah != 0)
         {
     printf ("Error mapping page %xH/n",
       outregs.h.ah);

     // Release the handle
     inregs.h.ah = 0x45;
     inregs.x.dx = handle;
     int86 (0x67, &inregs, &outregs);
     exit(0);
         }

       // Fill page 4 which resides in page 1
       for (index = 16384; index < 32768; index++)
         data[index] = 'E';

       // Display the first 20 bytes of each page
       printf ("Physical Page Zero/n");
       for (index = 0; index < 20; index++)
         printf ("%c ", data[index]);

       printf ("/nPhysical Page One/n");
       for (index = 16384; index < 16404; index++)
         printf ("%c ", data[index]);

       printf ("/nPhysical Page Two/n");
       for (index = 32768; index < 32788; index++)
         printf ("%c ", data[index]);

       printf ("/nPhysical Page Three/n");
       for (index = 49152; index < 49172; index++)
         printf ("%c ", data[index]);

       // Map logical page 1 into physical page 3
       inregs.h.ah = 0x44;
       inregs.h.al = 3; // Physical page
       inregs.x.bx = 1; // Logical page
       inregs.x.dx = handle;

       int86 (0x67, &inregs, &outregs);

       if (outregs.h.ah != 0)
         {
     printf ("Error mapping page %xH/n",
       outregs.h.ah);

     // Release the handle
     inregs.h.ah = 0x45;
     inregs.x.dx = handle;
     int86 (0x67, &inregs, &outregs);
     exit(0);
         }

       printf ("/nMapping logical page 1 to physical page 3");
       printf ("/nPhysical Page Three/n");
       for (index = 49152; index < 49162; index++)
         printf ("%c ", data[index]);

     }
   else
     printf ("Error getting base address %xH/n",
       outregs.h.ah);

   // Release the handle
   inregs.h.ah = 0x45;
   inregs.x.dx = handle;
   int86 (0x67, &inregs, &outregs);
       }
     else
       printf ("Error allocating 5 pages %xH/n",
  outregs.h.ah);
   }
else
printf ("EMM not functional/n");
      }
    else
      printf ("EMS driver not present/n");

}