ADC Home > Reference Library > Reference > Hardware & Drivers > I/O Kit Framework Reference

---

IODataQueueShared.h

Overview

This header contains data types and definitions common to both clients and providers of an I/O Kit data queue. These queues are typically used to allow a device driver or family to communicate a continuous stream of data to a client, such as might be required for an audio device serial port driver.

---

Typedefs

---

IODataQueueAppendix

---

A struct mapping to the appendix region of a data queue.

typedef struct _IODataQueueAppendix { 
    UInt32 version; 
    mach_msg_header_t msgh; 
} IODataQueueAppendix;  

Fields

version

The version of the queue appendix.

port

The notification port associated with this queue.

Discussion

This struct is variable sized dependent on the version. The struct represents the data queue appendix information.

---

IODataQueueEntry

---

Represents an entry within the data queue

typedef struct _IODataQueueEntry{ 
    UInt32 size; 
    UInt8 data[4]; 
} IODataQueueEntry;  

Fields

size

The size of the following data region.

data

Represents the beginning of the data region. The address of the data field is a pointer to the start of the data region.

Discussion

This is a variable sized struct. The data field simply represents the start of the data region. The size of the data region is stored in the size field. The whole size of the specific entry is the size of a UInt32 plus the size of the data region.

---

IODataQueueMemory

---

A struct mapping to the header region of a data queue.

typedef struct _IODataQueueMemory { 
    UInt32 queueSize; 
    volatile UInt32 head; 
    volatile UInt32 tail; 
    IODataQueueEntry queue[1]; 
} IODataQueueMemory;  

Fields

queueSize

The size of the queue region pointed to by the queue field.

head

The location of the queue head. This field is represented as a byte offset from the beginning of the queue memory region.

tail

The location of the queue tail. This field is represented as a byte offset from the beginning of the queue memory region.

queue

Represents the beginning of the queue memory region. The size of the region pointed to by queue is stored in the queueSize field.

Discussion

This struct is variable sized. The struct represents the data queue header information plus a pointer to the actual data queue itself. The size of the struct is the combined size of the header fields (3 * sizeof(UInt32)) plus the actual size of the queue region. This size is stored in the queueSize field.

#defines

---

DATA_QUEUE_ENTRY_HEADER_SIZE

---

#define DATA_QUEUE_ENTRY_HEADER_SIZE  

Discussion

Represents the size of the data queue entry header independent of the actual size of the data in the entry. This is the overhead of each entry in the queue. The total size of an entry is equal to this value plus the size stored in the entry's size field (in IODataQueueEntry).

---

DATA_QUEUE_MEMORY_APPENDIX_SIZE

---

#define DATA_QUEUE_MEMORY_APPENDIX_SIZE  

Discussion

Represents the size of the data queue memory appendix independent of the actual size of the queue data itself. The total size of the queue memory is equal to this value plus the size of queue header and size of the queue data region which is stored in the queueSize field of IODataQueueMeory.

---

DATA_QUEUE_MEMORY_HEADER_SIZE

---

#define DATA_QUEUE_MEMORY_HEADER_SIZE  

Discussion

Represents the size of the data queue memory header independent of the actual size of the queue data itself. The total size of the queue memory is equal to this value plus the size of the queue appendix and the size of the queue data region which is stored in the queueSize field of IODataQueueMeory.

Did this document help you? Yes: Tell us what works for you. It’s good, but: Report typos, inaccuracies, and so forth. It wasn’t helpful: Tell us what would have helped.

 

Last Updated: 2009-02-23