USB HOST DRIVER V03 Freescale Semiconductor / Motorola, USB HOST DRIVER V03 Datasheet - Page 27

• Manufacturer Part Number: USB HOST DRIVER V03
• Description: USB Host Driver v03
• Manufacturer: Freescale Semiconductor / Motorola

packets have to be less than or equal to the maximum packet size of the endpoint. There
must be no gaps between the data packets in the transfer buffer. The
member of the
transfer is started. Note that because the size of the received packets may be less than the
maximum packet size, data packets are not arranged continuously within the transfer
buffer.
When the MOTUSB Driver completes read I/O requests, it changes the
of each packet according to the actual bytes which were processed in that packet.
Normally this field should specify the total number of bytes read for a particular pipe.
3.4.3.
Using asynchronous (Overlapped) I/O means a thread does not need to wait for a request
completion, to be able to perform some task while the Driver processes the I/O request.
Overlapped I/O can be applied to any transfer type. If a Client wants to perform
overlapped operations, it should open a pipe by specifying the
file attribute parameter to the
related to the Device or pipe object, the caller should specify the
buffer pointer.
Overlapped I/O is very important for isochronous transfers. The major issue with these
transfers is that for the most part the Client application should deliver or receive data in
real time. When the application performs Read or Write request to the MOTUSB Driver,
the I/O System does not guarantee that this request will be available in the frame time
limit (1 millisecond normally). The only possible solution is to put several requests to the
Driver, wait until some of them complete and then put further requests with the
USB_ISO_TRANSFER_ASAP
3.5. Device Requests.
The I/O Control requests are submitted to the Driver using the Win32 function
DeviceIoControl
The
BOOL DeviceIoControl(
M
DeviceIoControl
HANDLE hDevice
DWORD dwIoControlCode
LPVOID lpInBuffer
DWORD nInBufferSize
LPVOID lpOutBuffer
DWORD nOutBufferSize
LPDWORD lpBytesReturned
Using Asynchronous I/O.
USB_ISO_PACKET
.
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
function is defined as follows:
,
flag set.
,
,
,
,
CreateFile
Programming Interface.
,
structures have to be initialized correctly before the
, // pointer to variable to receive
// output byte count
// handle to Device object
// control code of operation to perform
// pointer to buffer to supply input data
// size of input buffer
// pointer to buffer to receive output data
// size of output buffer
function. Then for each Win32 API call
FILE_FLAG_OVERLAPPED
OVERLAPPED
Offset
Length
and
structure
member
Length
3-5