WinUsb_ReadIsochPipeAsap function (winusb.h)
The WinUsb_ReadIsochPipeAsap function submits a request that reads data from an isochronous IN endpoint.
Syntax
BOOL WinUsb_ReadIsochPipeAsap(
[in] WINUSB_ISOCH_BUFFER_HANDLE BufferHandle,
[in] ULONG Offset,
[in] ULONG Length,
[in] BOOL ContinueStream,
[in] ULONG NumberOfPackets,
PUSBD_ISO_PACKET_DESCRIPTOR IsoPacketDescriptors,
[in, optional] LPOVERLAPPED Overlapped
);
Parameters
[in] BufferHandle
An opaque handle to the transfer buffer that was registered by a previous call to WinUsb_RegisterIsochBuffer.
[in] Offset
Offset into the buffer relative to the start the transfer.
[in] Length
Length in bytes of the transfer buffer.
[in] ContinueStream
Indicates that the transfer should only be submitted if it can be scheduled in the first frame after the last pending transfer.
[in] NumberOfPackets
Total number of isochronous packets required to hold the transfer buffer. Also indicates the number of elements in the array pointed to by IsoPacketDescriptors.
IsoPacketDescriptors
An array of USBD_ISO_PACKET_DESCRIPTOR that receives the details of each isochronous packet in the transfer.
[in, optional] Overlapped
Pointer to an OVERLAPPED structure used for asynchronous operations.
Return value
WinUsb_ReadIsochPipeAsap returns TRUE if the operation succeeds. Otherwise this function returns FALSE, and the caller can retrieve the logged error by calling GetLastError.
If the caller sets ContinueStream to TRUE, The transfer fails if Winusb.sys is unable to schedule the transfer to continue the stream without dropping one or more frames.
Remarks
WinUsb_ReadIsochPipeAsap allows the USB driver stack to choose the starting frame number for the transfer. If one or more transfers are already pending on the endpoint, the transfer will be scheduled for the frame number immediately following the last frame number of the last currently pending transfer.
WinUsb_ReadIsochPipeAsap packetizes the transfer buffer so that in each interval, the host can receive the maximum bytes allowed per interval. The maximum bytes is as specified by the endpoint descriptor for full and high-speed endpoints, and endpoint companion descriptor for SuperSpeed endpoints. If the caller submits multiple read requests to stream data from the device, the transfer size should be a multiple of the maximum bytes per interval (as returned by WinUsb_QueryPipeEx) * 8 / interval.
Because of the transfer packaging used in the underlying kernel-mode interface, the lowest latency notification to an application or driver is 1ms intervals.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows 8.1 |
| Minimum supported server | Windows Server 2012 R2 |
| Target Platform | Universal |
| Header | winusb.h (include Winusb.h) |
| Library | Winusb.lib |
| DLL | Winusb.dll |