Parker PHD28, User Manual, Page: 128 / 157

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J1939 Service
Appendix A
Instruction book, PHD API Reference
Appendix A
J1939 Service
The PHD J1939 service exists to provide the system with access to one or more J1939
CAN buses. Inter-process communication is provided via DCP to permit access from other
system services.
Features
• Send and receive of 8-byte messages
• Send and receive of long messages (up to and including 1785 byte payloads) using the
following mechanisms.
• Point to point - Long message exchange between precisely two connected
parties.
• Broadcast - Long message exchange to all interested parties within the broadcast
domain of the local network segment.
• J1939 network management, including address claim concession and defense.
• Support for SOFT (software identification) message.
• Automatic handling of RQST (request) messages.
Architecture
The service is formed of two primary components:
• The J1939 library (1042616, libj1939). This connects to the CAN device drivers to
provide send and receive communications with multiple CAN buses. The library
provides a full abstraction of the lower level interfaces to present an external interface
at the J1939 level in the protocol stack. Both C++ (native) and C (wrapper) interfaces
are provided.
• The J1939 service (1042618, j1939d). This component is the daemon which provides
the front end communication service and is the point of interaction for other
communicating processes. Operation is driven by a configuration file, allowing per-
application customization without recompilation of the core executable.
To promote code reuse, a common shared component is employed between the J1939
library and the J1939 service. This contains a library of common "helper" functions and
common definitions to be used by both components.
The J1939 service also requires the use of an external library to allow the user
configuration file to be read. The user configuration is specified in the form of a JavaScript
Object Notation (JSON) file and so a library capable of reading this is necessary; this is
currently implemented in libjson using JsonCpp which is released into the public domain
under the MIT license with only a requirement to include the author’s copyright
information.