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study/sabre/os/files/ProtectedMode/DPMI1.0Spec/api/310508.html

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+<h2>Map Device in Memory Block
+<img src="../1.0.gif" alt="[1.0]" width=22 height=17></h2>
+
+Maps the physical addresses assigned to a device onto the linear
+addresses of a memory block previously allocated with <a
+href="310504.html">Int 31H Function 0504H</a>.<p>
+
+<b>Call With</b><br>
+<img src="r/ax+ebx+ecx+edx+esi.gif" alt="" width=245 height=59><br>
+
+AX     = 0508H<br>
+ESI    = memory block handle<br>
+EBX    = offset within memory block of page(s) to be
+mapped (must be page-aligned)<br>
+ECX    = number of pages to map<br>
+EDX    = physical address of device (must be
+page-aligned)<p>
+
+<b>Returns</b><br>
+<img src="r/ax+c.gif" alt="" width=245 height=59><br>
+
+<i>if function successful</i><br>
+Carry flag = clear<p>
+
+<i>if function unsuccessful</i><br>
+Carry flag = set<br>
+AX     = <a href="errors.html">error code</a>
+
+<table border=1 cellspacing=0 cellpadding=4>
+
+<tr><td>8001H</td><td>unsupported function (Device Mapping</td></tr>
+Capability not supported)
+<tr><td>8003H</td><td>system integrity (invalid device address)</td></tr>
+<tr><td>8023H</td><td>invalid handle (in ESI)</td></tr>
+<tr><td>8025H</td><td>invalid linear address (specified range
+is not within specified block or EBX/EDX
+is not page-aligned)</td></tr>
+</table>
+
+<h2>Notes</h2><ul>
+
+
+<li>16-bit DPMI hosts will not support this function.  A 16-bit client
+of a 32-bit DPMI 1.0 host can use this function.<p>
+
+<li>Support of this call by 32-bit DPMI hosts is optional.
+Application programs or DOS Extenders which require this call in order
+to run are not DPMI Compliant.<p>
+
+<li>Any committed or mapped pages resided in the linear address range
+that is being mapped into will be uncommitted or unmapped
+automatically by the host.<p>
+
+<li>All pages created by this call have the mapped bit (bit 2) set in
+the attributes returned by the Get Page Attributes function (<a
+href="310506.html">Int 31H Function 0506H</a>).<p>
+
+<li>This function differs from the Create Physical Address Mapping
+function (<a href="310800.html">Int 31H Function 0800H</a>) in that
+this function supports mapping of physical devices within an existing
+memory block, rather than at an arbitrary linear address.  Use of an
+existing memory block gives 32-bit programs the ability to access
+physical devices with NEAR pointers, which is often highly desirable
+for performance reasons.<p>
+
+<li>Unlike <a href="310800.html">Int 31H Function 0800H</a>, this
+function allows mapping of addresses below 1 MB that do not lie within
+RAM available for use by programs; e.g. this function can be used to
+map the refresh buffers of IBM-compatible display adapters.<p>
+
+<li>If the DPMI host is not virtualizing the device, it must disable
+any memory caching on the mapped pages; in particular, on the 486 or
+later, the PCD (page cache disable) bit must be set in the page table
+entries.<p>
+
+<li>DPMI hosts that do not virtualize physical devices can support
+this function by creating page table entries that map the physical
+device.  The page table entries must be marked as mapped so that the
+host knows not to attempt freeing of physical memory for the pages
+when the memory block is freed.<p>
+
+<li>DPMI hosts are allowed to support this function for some physical
+devices and not for others, because mapping of virtualized devices
+requires page aliasing in the host - a complex task.  DPMI hosts with
+partial support for this function may fail the function call on
+virtualized devices (such as displays), and allow the call on
+non-virtualized devices (such as the Weitek coprocessors).  Allowing
+the client to map a physical device so that it can be accessed with
+NEAR references, for example, may help the client achieve considerably
+better performance.<p>
+
+</ul>
+
+