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USBIsocWrite

The USBIsocWrite function supports isochronous write transactions, and is defined as follows:

Required fields in the isochronous version of the USBPB parameter block for the USBIsocWrite function are

--> pbLength

Length of parameter block

--> pbVersion

Parameter block version, must be kUSBIsocPBVersion for isochronous function calls

<--usbStatus

Aggregate status, see discussion in The Isochronous Version Of The USBPB

--> usbCompletion

The completion routine

--> usbRefcon

General-purpose value passed back to the completion routine

--> usbReference

The isochronous pipe reference returned by the USBFindNextPipe or USBOpenPipe functions

--> usbReqCount

Specifies the size of the data to transfer. If this is set to 0 in the frReqCount field in the frame structure, the call sends a packet size of 0.

--> usbBuffer

Points to the data to be transferred. The buffer should be at least as big as the size specified in the usbReqCount field. If the buffer is set to nil , no data is transferred regardless of the value of usbReqCount

<-- usbActCount

Specifies the actual amount of data transferred on completion

--> usbFlags

Should be set to 0

--> usb.isoc.FrameList

Pointer to the list of frame structures

--> frReqCount  Number of bytes requested for each packet

<-- frStatus    Status returned by packet

<-- frActCount  Actual bytes transferred by packet

--> usb.isoc.NumFrames

Number of frames to attempt transfers in

--> usbFrame

Frame number of the first frame to transfer data

A complete discussion of how isochronous support is implemented and additional details about using the fileds in the isochronous version of the USBPB parameter block can be found in Using the USBPB For Isochronous Transactions .

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