PATHHardware Documentation > USB Devices > Mac OS USB DDK API Reference

USBIsocRead

Isochronous data transfers are supported in version 1.1 and higher of the Mac OS USB software.

The USBIsocRead function supports isochronous read data transfers, and is defined as follows:

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

--> usbReqCount

Specifies the size of the data to transfer. May be any size, but no less than the sum of the individual packets sizes. If set to 0, any non-zero size transfer causes an error.

--> usbBuffer

Points to a buffer to which the incoming data is transferred

<-- 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 .

Previous | Back Up One Level | Next | Show Frames | Hide Frames