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# sendIORequest(with:frameList:frameListCount:firstFrameNumber:)

Sends a request on an isochronous endpoint.

```
func sendIORequest(with data: NSMutableData, frameList: UnsafeMutablePointer<IOUSBHostIsochronousFrame>, frameListCount: Int, firstFrameNumber: UInt64) throws
```

## Parameters

`data`

An <doc://com.apple.documentation/documentation/Foundation/NSMutableData> object defining the memory to use for the transfer.

`frameList`

A pointer to the first element in an [`IOUSBHostIsochronousFrame`](/documentation/IOUSBHost/IOUSBHostIsochronousFrame) array. The array must contain at least `frameListCount` elements.

`frameListCount`

The number of elements in `frameList`.

`firstFrameNumber`

The frame number the request begins on. Query the current frame number with [`frameNumberWithTime:`](/documentation/IOUSBHost/IOUSBHostObject/frameNumberWithTime:). If `0`, the transfer starts on the next available frame (XHCI only).

## Discussion

This method issues synchronous isochronous requests. The caller allocates and initializes an array of [`IOUSBHostIsochronousFrame`](/documentation/IOUSBHost/IOUSBHostIsochronousFrame) structures to describe the transferred frames.

---

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