AVCSTRM_OPEN
The AVCSTRM_OPEN function code opens a stream with a specific stream format.
I/O Status Block
If successful, avcstrm.sys sets Irp->IoStatus.Status to STATUS_SUCCESS.
If successful, a STATUS_SUCCESS is returned along with the stream context in AVCStreamContext member of the AVC_STREAM_REQUEST_BLOCK structure. This context is subsequently used for other avcstrm.sys requests.
Possible error return values include:
| Error Status | Description |
|---|---|
| STATUS_DEVICE_REMOVED | The device corresponding to the AVCSTRM_READ operation no longer exists. |
| STATUS_CANCELLED | The request was unable to be completed. |
| STATUS_INVALID_PARAMETER | A parameter specified in the IRP is incorrect, |
| STATUS_INSUFFICIENT_RESOURCES | There were not sufficient system resources to complete the request. |
| STATUS_PENDING | The request has been received but requires further processing. The I/O completion routine will handle the final response. |
AVC_STREAM_REQUEST_BLOCK Input
SizeOfThisBlock, Version and Function
Use the INIT_AVCSTRM_HEADER macro to initialize these members. Pass AVCSTRM_OPEN in the Request argument of the macro.
AVCStreamContext
Specifies the stream context (handle). This should be NULL on input, and if AVCSTRM_OPEN returns successfully, this member contains a valid stream context for subsequent avcstrm.sys operations.
OpenStruct
Specifies the description of the AV/C stream to be created.
The AVCSTRM_FORMAT enumeration provides the list of supported AV/C streaming formats (from the IEC 61883 specifications) that avcstrm.sys supports, such as SDDV (61883-2) and MPEG2TS (61883-4).
In order to make an isochronous connection, the CIP headers and subunit dependent parameters are required and are defined in the AVCSTRM_FORMAT_INFO structure.
The following is an example of the MPEG2TS format information for receiving data:
//
// MPEG2TS
//
{
sizeof(AVCSTRM_FORMAT_INFO),
AVCSTRM_FORMAT_MPEG2TS,
{
0,0,
CIP_SPH_MPEG,
CIP_QPC_MPEG,
CIP_FN_MPEG,
IP_DBS_MPEG,
0,0
}, // CIP header[0]
{
0,0,0,
CIP_TSF_OFF,
CIP_FMT_MPEG,
2,
}, // CIP header[1]
SRC_PACKETS_PER_MPEG2TS_FRAME, // varies depending on number of source packets
BUFFER_SIZE_MPEG2TS_NO_SPH, // Remove source packet header
NUM_OF_XMT_BUFFERS_MPEG2TS, // Subunit defined
0,
FALSE, // not striping SPH is the default
0,
BLOCK_PERIOD_MPEG2TS, // 192, / number of 1394 cycle offset to send one block
0,0,0,0,
},
A subunit driver must first allocate an IRP and an AVC_STREAM_REQUEST_BLOCK structure.
Next, it should use the INIT_AVCSTRM_HEADER macro to initialize the AVC_STREAM_REQUEST_BLOCK structure, passing AVCSTRM_OPEN as the Request argument to the macro.
Next, the subunit driver sets the AVCStreamContext member to NULL.
On successful operation, this member should contain a valid stream context (a handle) that is used in subsequent avcstrm.sys operations. This member should not be modified thereafter until the stream is closed through AVCSTRM_CLOSE.. Finally, the subunit driver sets the OpenStruct member of the CommandData union that describes the stream to be opened.
To send this request, a subunit submits an IRP_MJ_INTERNAL_DEVICE_CONTROL IRP with the IoControlCode member of the IRP set to IOCTL_AVCSTRM_CLASS and the Argument1 member of the IRP set to the AVC_STREAM_REQUEST_BLOCK structure that describes the open operation to take place.
A subunit driver can expect this command to complete synchronously. The result returns immediately without pending operation in avcstrm.sys.
This function code must be called at IRQL = PASSIVE_LEVEL.
Comments
This function uses the OpenStruct member of the CommandData union in the AVC_STREAM_REQUEST_BLOCK structure as shown below.
typedef struct _AVC_STREAM_REQUEST_BLOCK {
ULONG SizeOfThisBlock;
ULONG Version;
AVCSTRM_FUNCTION Function;
.
.
PVOID AVCStreamContext;
.
.
union _tagCommandData {
.
.
AVCSTRM_OPEN_STRUCT OpenStruct;
.
.
} CommandData;
} AVC_STREAM_REQUEST_BLOCK, *PAVC_STREAM_REQUEST_BLOCK;
Requirements
Headers: Declared in avcstrm.h. Include avcstrm.h.