PTP Overview

Bear Lin

2009/04/28

Outline

Terms & Definitions

Introduction

Purpose

Data Format Specification

Image and Data Object Formats

Persistent Storage

Communication Protocol

Operations

Responses

Events

Device Properties

Terminology

PTP (Picture Transfer Protocol)

DSPDs (Digital Still Photography Devices)

Introduction

This standard is designed to provide requirements for

communicating with DSPDs.

This includes communications with any type of device, including

host computer, direct printers and other DSPDs over a suitable

transport.

The requirements includes: Standard image referencing behavior.

Operations.

Responses.

Events.

Device properties.

Datasets.

Data formats.

This standard has been designed to appropriately support popular

image formats used in digital still cameras, including the EXIF and

TIFF/EP formats as well as DCF and DPOF.

Purpose

The primary purpose:

To provide a common protocol for any device, including DSPDs, to

exchange images with a DSPD.

The Secondary purpose:A mechanism for devices to control DSPDs(e.g. a PC can request that a

DSPD change its shutter duration setting and capture a new picture), and

the ability to transfer auxiliary information(such as non-image data files)

and associated information(such as a DPOF file).

Data Format Specification

Data Format Specification(cont.)

Data Format Specification(cont.)

Image and Data Object Formats

A data object is defined to be an image or other type of

data that exists in persistent storage of a DSPD or

other device.

For all image and data objects, an ObjectFormatCode

is provided in the ObjectInfo dataset to specify the

format.

Image and Data Object Formats(cont.)

Persistent Storage

Every storage area on a device is represented by a unique, 4-byte,

unsigned integer(UINT32) referred to as a StorageID.

A physical store may possess zero or more logical stores.

The StorageIDs for all logical stores within a physical store shall have the

same PhysicalStorageID.

PhysicalStorageIDs are unique for a particular device at all times.

LogicalStorageIDs within that physical store shall be unique.

LogicalStorageIDs need only be unique within a physical store, and not

globally across all stores.

Communication Protocol

Device Roles: This standard will only refer to two devices, an Initiator and a

Responder.

The Initiator(PC) is the device that opens the session and initiates

operation requests over a suitable transport according to that

transport’s implementation specification.

A Responder(USB-only camera) is a device that responds to

operation requests by sending requested data, responses, and

events.

Sessions: Sessions are defined as logical connections between two devices,

over which ObjectHandles and StorageIDs are persistent.

Communication Protocol(cont.)

Transactions: All transactions are considered atomic invocations whose origins can

be traced to a single operation request being issued by an Initiator to a

Responder.

Only one transaction at a time can take place within a session.

A transaction may be cancelled by an event.

Communication Protocol(cont.)

Operation Request Phase: Consists of the transport-specific transmission of the 30-byte

operation dataset from the Initiator to the Responder.

Communication Protocol(cont.)

Data Phase: Is a optional phase. Typically, this is either a data object such as an

image, an ancillary data file, or other datasets that are defined in this

standard or are vendor extensions.

The format for data transferred during a data phase is context-specific

by operation and ObjectFormat.

It is the responsibility of the transport-implementation to specify how

the data should be handle, wrapped, and re-assembled.

Communication Protocol(cont.)

Response Phase: Consists of the transport-specific transmission of the 30-byte response

dataset from the Responder to the Initiator.

Communication Protocol(cont.)

Event Dataset: Events are described using the Event Dataset which consists of the

minimal information that is required for qualified notification.

Communication Protocol(cont.)

Operation Flow: Push mode: An initiator sending one or more objects to the

Responder.

Pull mode: The Initiator retrieves objects from the Responder.

Pull Scenarios: Initiator requests all image objects from the Responder.

Communication Protocol(cont.)

Push Scenarios: The Initiator pushes all objects to the Responder, allowing the

Responder to determine where to place the objects it is retrieving.

Operations

Operations(cont.)

Responses

Events

USB Implementation of PIMA15740

USB Implementation of PIMA15740(cont.)

USB Implementation of PIMA15740(cont.)

Still Image Capture Device Class-Specific Protocol: Three phases of operation execution(applies to the Bulk-Only

Protocol) are Command, Data, and Response.

USB Implementation of PIMA15740(cont.)Endpoint Utilization in Still Image Bulk-only Protocol:

USB Implementation of PIMA15740(cont.)Bulk-Pipe Containers:

USB Implementation of PIMA15740(cont.)Asynchronous Event Interrupt Data Format: