161 lines
8.7 KiB
HTML
161 lines
8.7 KiB
HTML
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<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=windows-
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1252">
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<META NAME="Generator" CONTENT="Microsoft FrontPage 5.0">
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<TITLE>Iso Usb</TITLE>
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</HEAD>
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<BODY LINK="#0000ff">
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<p><b><font face="Times New Roman">The Isousb driver</font></b></p>
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<ul>
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<li><font face="Times New Roman">The isousb driver is function driver, based on the
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Windows Driver Model (WDM).</font></li>
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<li><font face="Times New Roman">Supports Plug and Play(PnP), Power
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Management(PM), Windows Management Instrumentation (WMI) and the Selective
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Suspend (SS) features.</font></li>
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<li><font face="Times New Roman">This sample is based off the selSusp sample
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in the DDK. Please refer the selSusp sample and the DDK docs to understand the
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handling of PnP, PM, WMI and SS features and implementations.</font></li>
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<li><font face="Times New Roman">The USB device used for this sample is a
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generic Intel I82930 USB evaluation board programmed with a simple loopback
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test using a 64KB circular buffer. None of the code in the sample is specific
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to this controller chip</font></li>
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</ul>
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<p><font face="Times New Roman">This section describes the driver routines that
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allow a user-mode application to perform isoch reads and writes or stream
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transfers. The isoch read/write is performed by opening a handle to the device
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and using the standard Win32 Read/Write command. The stream transfer is a
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continuous streaming of isoch IN data which can be explicitly initiated/stopped
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using the driver-supported IOCTLs from the user application.</font></p>
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<p><b>Isousb Reads/Writes and Stream Transfers<br>
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</b></p>
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<table border="1" width="68%">
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<tr>
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<td width="50%"><font face="Courier New">Requests</font></td>
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<td width="50%"><font face="Courier New">Dispatch Routines</font></td>
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</tr>
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<tr>
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<td width="50%"><font face="Courier New">IRP_MJ_CREATE</font></td>
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<td width="50%"><font face="Courier New">IsoUsb_DispatchCreate()</font></td>
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</tr>
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<tr>
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<td width="50%"><font face="Courier New">IRP_MJ_CLOSE</font></td>
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<td width="50%"><font face="Courier New">IsoUsb_DispatchClose()</font></td>
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</tr>
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<tr>
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<td width="50%"><font face="Courier New">IRP_MJ_READ</font></td>
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<td width="50%"><font face="Courier New">IsoUsb_DispatchReadWrite()</font></td>
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</tr>
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<tr>
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<td width="50%"><font face="Courier New">IRP_MJ_WRITE</font></td>
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<td width="50%"><font face="Courier New">IsoUsb_DispatchReadWrite()</font></td>
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</tr>
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<tr>
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<td width="50%"><font face="Courier New">IOCTL_ISOUSB_START_ISO_STREAM</font></td>
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<td width="50%"><font face="Courier New">IsoUsb_StartIsoStream()</font></td>
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</tr>
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<tr>
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<td width="50%"><font face="Courier New">IOCTL_ISOUSB_STOP_ISO_STREAM</font></td>
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<td width="50%"><font face="Courier New">IsoUsb_StopIsoStream()</font></td>
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</tr>
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</table>
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<p>Notes</p>
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<ul>
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<li>The <font face="Courier New">IsoUsb_DispatchCreate()</font> allows a user-mode app. to open handles to the
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device or to the pipe.</li>
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<li>Pipe # 5 and Pipe # 6 correspond to the Isoch IN and Isoch OUT
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respectively. The driver does not hard-code the pipe # for reads and writes.</li>
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<li>The <font face="Courier New">IsoUsb_DispatchClose()</font> closes the
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handles to the pipe or the device</li>
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</ul>
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<p><b>Stream Transfers</b></p>
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<ul>
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<li>The driver routines which implement this functionality are:<br>
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<font face="Courier New">IsoUsb_StartIsoStream()<br>
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IsoUsb_StopIsoStream()<br>
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IsoUsb_InitializeStreamUrb()<br>
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IsoUsb_IsoIrp_Complete()<br>
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IsoUsb_ProcessTransfer()<br>
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IsoUsb_StreamObjectCleanup()<br>
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</font></li>
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<li>The stream transfer can be initiated from a device control request.</li>
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<li>The stream transfer comprises of continuous streaming IN of data.</li>
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<li>The stream transfer circulates <font face="Courier New">ISOUSB_MAX_IRP</font>
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number of requests at any time.</li>
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<li>The stream transfer stops on receiving an explicit device control
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request or when the user-mode app. terminates or stops.</li>
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<li>The stream transfer context information is maintained in the <font face="Courier New">ISOUSB_STREAM_OBJECT</font>
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structure. This structure is saved in the FileObject pointer.</li>
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<li>There are ISOUSB_MAX_IRP number of Irp/Urb pairs which are re-circulated
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and used for transfers. The ISOUSB_TRANSFER_OBJECT structure maintains
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context information for each of the Irp/Urb pair.</li>
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<li><font face="Times New Roman">In order to stop or abort the transfer, the
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routine </font><font face="Courier New">IsoUsb_StreamObjectCleanup</font><font face="Times New Roman">
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cancels the re-circulating Irps and waits on an event triggered by the
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completion routine for the last cancelled Irp. Thereafter, it proceeds to
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release memory allocation for the stream object and the transfer objects.</font></li>
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<li><font face="Times New Roman">Since the driver saves the stream object
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structure in the FileObject, it is multi-threaded safe accross applications,
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but with a major caveat. The user applications should not use the same handle
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to initiate multiple stream transfers. This functionality can be easily
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supported by forming a list of stream-object structures in the FileObject
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(rather than storing a single stream object structure). </font></li>
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</ul>
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<p><b>Isoch Reads/Writes</b></p>
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<ul>
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<li><font face="Times New Roman">The Isoch read/write transfer requires an Irp/Urb
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pair with the function code of URB_FUNCTION_ISOCH_TRANSFER.</font></li>
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<li>There is an upper bound on the number of packets that can be transferred
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with each of the Irp/Urb pair and is given as 255. This calls for creating
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multiple subsidiary Irp/Urb pairs to transfer the requested length of data.</li>
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<li><font face="Times New Roman">The </font><font face="Courier New">IsoUsb_DispatchReadWrite</font><font face="Times New Roman">
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creates the required number of subsidiary Irp/Urb pairs,
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initializes them and sets a completion routine (</font><font face="Courier New">IsoUsb_SinglePairComplete</font><font face="Times New Roman">)
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for each of the Irp in the pair </font></li>
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<li>The dispatch routine sets <font face="Times New Roman">a cancellation
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routine (</font><font face="Courier New">IsoUsb_CancelReadWrite</font><font face="Times New Roman">)
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for the original read/write Irp and pends the Irp.</font></li>
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<li><font face="Times New Roman">The dispatch routine now passes the
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subsidiary Irp/Urb pair down the stack.</font></li>
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<li>It is possible to abort the read/write transfers at any point. It is the
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responsibility of the driver to cancel/free the Irp/Urb pairs, release all
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resources and terminate gracefully.</li>
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<li><font face="Times New Roman">The </font><font face="Courier New">IsoUsb_DispatchReadWrite,
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IsoUsb_SinglePairComplete
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</font><font face="Times New Roman">and
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</font><font face="Courier New">IsoUsb_CancelReadWrite</font><font face="Times New Roman">
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routines are well annotated with comments to aid understanding.</font></li>
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<li><font face="Times New Roman">Since the driver does not save the read-write
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context information in the driver, but passes it to the completion routine, it
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is multithreaded safe.</font></li>
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</ul>
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<p><b><font face="Times New Roman">High Speed Isoch Reads/Writes</font></b></p>
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<ul>
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<li><font face="Times New Roman">The DDK sample has been updated for high
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speed isoch transfers.</font></li>
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<li><font face="Times New Roman">There are two significant differences between
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high speed and full speed transfers:<br>
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a. The upper bound on the number of packets that can be transferred with each
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Irp/Urb pair is 1024.<br>
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b. The number of packets sent down with each Irp/Urb pair should be a multiple
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of 8.</font></li>
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<li><font face="Times New Roman">The </font><font face="Courier New">
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PerformHighSpeedIsochTransfer</font><font face="Times New Roman"> gives one
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implementation of creating multiple of 8 packets.</font></li>
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</ul>
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<p><b><font face="Times New Roman">Known Bugs</font></b></p>
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<ul>
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<li><font face="Times New Roman">When the Intel I82930 evaluation board is
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used to perform loopback transfers with OUT transfers not in multiple of 8,
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the IN pipe is stalled. This can be attributed to the firmware error.
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Resetting the pipe does not solve this problem. This requires reconfiguring
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the device or driver unload/load. </font></li>
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</ul>
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<p><b>RwIso.exe</b></p>
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<p>RwIso.exe is a console application used to initiate isochronous transfer and
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obtain a dump of information on the device's I/O endpoints. The application also
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demonstrates how to use GUID-based device names and pipe names generated by the
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operating system using the SetupDiXXX user-mode APIs.</p>
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</BODY>
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</HTML>
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