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Embedded Applications

ZCM prides itself on strong support for embedded applications. This support allows embedded systems to construct and send zcmtypes though a custom embedded transport to other systems using ZCM.

The core nonblock library code follows the following principles:

  1. Standard-compliant C89 code
  2. Absolutely no dependencies (this includes any OS primitives)
  3. No blocking for any reason
  4. Designed for single-threaded use
  5. Minimal malloc() use. Currently, on startup only.

Platform Requirements

While we strive to support many systems, there are a few requirements:

  • byte-addressable memory
  • 8-bit, 16-bit, 32-bit and 64-bit signed and unsigned integer types
    • Some may be emulated, but the standard C integer types must be available
  • a basic C standard library
  • malloc implementation

Adding ZCM to a project

By default, the ZCM linux build gathers together the embedded-specific sources, checks them for C89 compliance, and creates build/zcm/zcm-embed.tar.gz. Using ZCM is as simple as untaring into your project's source tree. We recommend using the zcm subdir for all zcm library code.

For the generation of zcmtypes, you will need a standard linux ZCM install. You can simply use zcm-gen and copy the resulting files into your project's source tree.

With some scripting, most embedded environments can be configured to use zcm-gen as a build tool and all of the type generation can be made automatic.

Using ZCM in code

In embedded ZCM there are no built-in transports. To use ZCM in an embedded application, you must implement a nonblocking transport that uses your platform's hardware primatives. In addition, the transport registrar and the url system is disabled. To create a zcm_t object, you must use zcm_create_from_trans(). See the page on Transport Layer for details on implementing nonblocking transports. Note that the nonblocking api semantics are different than the blocking ones which makes zcm more friendly to embedded applications. Make sure you read the section on Non-blocking API Semantics carefully. Once implemented and constructed, you should be able to use ZCM the same way you would on desktop systems! A generic serial transport is provided for you. An example of how to use it is provided in the examples directory.

Issues, Bugs, and Support

In embedded-land it's hard to guarantee that a library will work on any system. We care a lot about our compatibility on embedded, but issues do happen. We always try to be proactive in our handling of any issues that arise. If you find any violations with the principles and requirements above, don't hesitate to reach out to the ZCM community. See Contributing for details.

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