TCF

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What is the Target Communication Framework (TCF)?

The Target Communication Framework (TCF) is a proposed addition to the Eclipse Target Management Project. Until accepted by the Eclipse Legal IP Clearance process, TCF as well as discussions regarding it are available from bugzilla on bug 210751 under the Eclipse Public License (EPL).

TCF is a vendor-neutral, lightweight, extensible network protocol mainly for communicating with embedded systems (targets). Its most distinguishing feature is that TCF is designed to transparently plug in value-adding servers between the tool and the target. The protocol has a transport-agnostic channel abstraction, so it does not depend on any specific transport such as TCP/IP, Serial Line, SSH tunnel or other. It uses JSON as preferred data marshaling language and supports auto-discovery of services. TCF is not restricted to Eclipse-based tools alone - there may be bindings to a variety of programming languages and environments. TCF is designed to become a replacement for protocols like GDB Serial, WDB, GDB/MI protocols used for embedded software development.

On top of the protocol specification, which is the core of TCF, the initial contribution includes a plain-C reference implementation of a lightweight extendable target agent with small footprint, as well as a Java client API (usable stand-alone or on top of Eclipse), documentation and usage examples. Future bindings may be for plain-C clients (like a gdb back-end plugin), tighter Eclipse integration (with the Eclipse Communication Framework (ECF)), or other.

For more details, see the Tool_Target_Communication_Vision_v5.ppt (440K) presentation.

How can I get more involved?

The TCF Protocol

What is so special about the TCF protocol?

  • TCF makes it simple to add value-adding servers into the host-target communication link: Instead of wrapping higher-level services like piggypack on top of lower ones, all services are on the same protocol layer. Therefore, servers can be plugged into the communication link transparently - no matter whether it's a hardware or software component. An example of a value-adding server is a debug engine providing translation between high-level language and assembly language debugging, or OS awareness adding information like which process or thread is currently executing when the target does not explicitly provide such information.
  • TCF provides for tunneling, addressing and auto-discovery all through one single, simple protocol such that the target agent can be small and lightweight. A reference implementation of such a lightweight agent is included for Linux, Windows and VxWorks.
    • There is a single abstraction for a "Channel" to support message-based host/target communication. Currently, channels are supported on TCP/IP only, but other communication and addressing schemes can be added easily. All higher-level services operate on the Channel abstraction.
  • The Tool_Target_Communication_Vision_v5.ppt (440K) presentation quite nicely shows this idea of all tools and value-added components just talking a single protocol with a single configuration over a single link on slides 4-7.

What Layers of the OSI Model does TCF address?

In terms of the OSI Model, TCF addresses layers 5 - 7: reliable end-to-end transport is currently assumed to be available from underlying carriers. TCF cares for (5) Session Layer - Interhost communication; (6) Presentation Layer - Data representation and encryption through JSON; (7) Application Layer - TCF Services can be seen as Applications.

Determining on where TCF will be applied, it could also provide services for the (3) Network Layer - Path determination and logical addressing (IP) as well as the (4) Transport Layer - End-to-end connections and reliability (TCP) in the future, simply by implementing the TCF "Channel" abstraction with such lower level transport services as well.

The TCF Contribution

What is included in the TCF contribution?

In addition to the core Protocol and associated documentation, the initial contribution also consists of:

  • Definition of some core services:
    • Locator (for addressing)
    • Remote File Access (File System Service)
    • Remote Process List (System Monitor Service)
    • Several Debug Services (Memory, Run Control, Registers, Stacktrace, Breakpoints).
  • A reference agent implementation in plain C, tested on Linux, Windows and VxWorks
  • A reference client implementation in Java
  • Example tools using the services:
    • Remote System Explorer (RSE) file service implementation, for remote file browsing
    • RSE process service implementation, for remote process browsing
    • Eclipse Debug Platform integration for debug demo
    • DSDP-DD integration of core DD services.

Where can I get TCF, and how do I get started?

Get the contribution archive from bug 210751, extract the archive and look at the documentation rooted at docs/index.html . The TCF Getting Started document, which is also part of the documentation, shows how to build and set up a Workspace with TCF.

How is TCF licensed?

The initial TCF contribution is being made under the Eclipse Public License (EPL) v1.0. This license is valid even before the Eclipse Foundation finished their IP review, so you can start using it right away.

What other components does TCF depend on?

The core TCF protocol is just a specification, so it does not depend on anything -- the protocol can be implemented in any language within any environment.

The reference agent can currently be built on Linux, Windows and VxWorks and uses POSIX services only. Depending on what Services the agent should implement, an ELF reader (libelf) is required to perform debug line number translation. Currently, this is done on Linux only.

The Java core protocol client also does not have any particular dependencies.

The RSE, Platform Debug, and DSDP-DD example tools depend on the RSE, Platform Debug and DSDP-DD components respectively.

Where can I ask questions about TCF?

Write an E-Mail to the dsdp-tm-dev@eclipse.org mailing list.

How does TCF compare to ECF?

TCF is a "vertical" technology stack: it includes all components needed to communicate with embedded remote systems en-to end. This includes the plain C lightweight target agent, the TCF protocol specification at its core, the Java protocol API as well as 3 example clients.

ECF, on the other hand, is a "horizontal" technology: it deals with Eclipse Java APIs for a host of different protocols for any kind of communication needs. ECF wants to unify the usage patterns on the client side, such that protocols are exchangeable.

Therefore, the intersection (overlap) of TCF and ECF is on the Java client API, which makes up for about 20% of the TCF contribution. Here are some thoughts on that overlap:

  • Both TCF and ECF have asynchronous APIs (request/callback and publish/subscribe, respectively).
  • Both TCF and ECF have APIs for remote file transfer and discovery. The means for addressing are different, though: URIs in ECF vs. simple IP address with implicit TCF protocol in TCF. Only TCF currently supports remote browsing (directory retrieval).
  • TCF currently supports point-to-point communications only, whereas ECF supports one-to-many and many-to-many communications (The underlying metaphor is "Joining a communications container").
  • ECF's charter to strive for generic interfaces makes it hard to prototype new communication protocols, or to drive features that one protocol has but another has not. The API is either the least common denominator of all protocols to be supported, or it has to provide mechanisms for querying remote capabilities such that features can be enabled/disabled - which makes using such interfaces harder for the client.

Summing up, it seems that while TCF is still incubating, it will be easier to stick with a Java API that's defined in TCF alone and develop the contribution under the DSDP/TM project; issues with dependencies and release cycles would otherwise make it unnecessarily complex to evolve the TCF protocol that's at the core of the contribution. At the same time, however, technology should be transferred between TCF and ECF as follows:

  • TCF means for general API access, addressing and discovery should be reviewed and potentially aligned with the corresponding ECF mechanisms, to ensure that clients don't need to learn multiple programming paradigms for communications, and to ensure that TCF and ECF can eventually be combined to a single API.
  • ECF APIs should be reviewed and/or extended to provide the features required by TCF, such that TCF fileshare and discovery implementations can eventually be implemented on top of ECF interfaces (thus TCF being just another ECF provider).

For more details, see also DSDP/TM/TCF - ECF Sync-up and Integration Meeting 4-Dec-2007

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