MILCAN

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MILCAN Adapting COTS CANbus to Military
Vetronics
Steven T. Majoewsky
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MILCAN

• Introduction
• Development
• Organization
• Progress
• Determinism
• Status

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MILCAN Introduction

• Who we are
• Why we are
• What are the Goals

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MILCAN Introduction

• Who we are
• Subgroup of IHSDBUG
• Formed in 1998
• Both industry and government representation
• United Kingdom
• Canada
• Sweden
• United States
• Germany

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MILCANIntroduction

• Why we are
• Apply low-cost CAN technology to military
  vehicles
• Address timing and latency issues
• Establish guidelines for common usage
• Component suppliers
• Vehicle manufacturers
• Countries

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MILCAN Introduction

• Why we are
• More is better, but the Northern Alliance is
  using Russian equipment as well as equipment
  purchased on the black market. There is British
  equipment as well as U.S. equipment. The
  interoperability iswell, rather a sticky
  wicket.
  .
  
  
  Lt. Col. Tim Eads, ret.

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MILCAN Introduction

• What are the Goals
• Create message structure connectivity
  guidelines for using CANbus in military ground
  combat vehicles
• Use off-the-shelf hardware
• Make Interoperability Easier

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MILCANIntroduction

• Goals continued
• Provide for real-time deterministic data transfer
• Use SAE J1939 and ISO 1198 to max extent
• Easily bridgeable

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MILCAN Development

• Built upon J1939 and ISO 11898
• Military Vehicles - Roots in Automotive CAN
  applications
• Militarized hardware

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MILCANDevelopment

• Create Simplified message ID structure
• Fits within J1939
• Create protocol for optional deterministic
  message transfer
• Create guideline documents

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MILCAN Organization

• 3 documents produced
• Physical layer
• Data Link layer
• Application layer

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MILCAN Organization

• Physical layer
• Opto-coupled
• Very large currents in vehicles
• Large ground-bounce
• In-cable power
• Polarity of connectorization important
• EMI/EMC considerations
• Shielded bus
• Military connectors

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MILCAN Organization
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MILCAN Organization
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MILCAN Progress

• Data Link layer
• 29-bit addressing MILCAN A
• Bit 25 used as Protocol Type Bit
• J1939/ISO11898 sets to 0
• MILCAN sets to 1
• 11-bit addressing MILCAN B
• Based on CANopen

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MILCAN Progress

• Data Link layer
• Multi-Frame Messages
• Primary/Sub Type specifies which messages have
  multiple frames
• 1st byte of payload is sequence number
• Sequence numbers range from 1 to 249
• J1939 compatibility
• Sequence number 250 signals end of message

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MILCAN Progress

• Application layer
• Simple, Flexible message identifier scheme
• Easy to implement hardware filtering
• Support multiple instances of same device
• Instance specification in payload byte
• Separate function identity from physical address
• Hand controller as example

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MILCAN Progress
28 26 25 24 23 16 15
8 7 0
Primary Type
Sub Type
Source Address
Priority
1
0
MILCAN Frame Identifier
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MILCANProgress

• Typical Primary Types
• Motion Control
• Fire Control
• Defensive Aid Suite
• Battle Management System

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MILCANDeterminism

• Support for both real-time deterministic messages
  and random event-driven messages simultaneously

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MILCAN Determinism

• High priority sync message establish timing on
  bus
• Sync message payload contains rotating time slot
  number
• Real-time deterministic messages assigned higher
  priority
• Transmitted in response to proper time slot
  number sync message
• Non-real-time messages fit into gaps

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MILCANDeterminism

• One bus sync generator at any given time
• Simple sync claim arbitration process can
  establish one of many possible nodes as sync
  generator
• If one sync generator fails, another will take
  over

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MILCANDeterminism

• Timing
• Concerns
• Jitter
• Drift

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MILCANDeterminism

• Timing
• Solution
• Allow time reserve
• Remember, this is COTS application

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MILCAN Determinism

• Sync message rate determines Primary Time Unit
  (PTU)
• Sync message payload contains time slot value
• Number of time slot values defines slowest
  deterministic repetition rate

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MILCAN Determinism

• Message Priorities
• 0 Protocol Operation Messages (sync)
• 1 HRT 1 1 PTU --4 SRT 1 8 PTU
• 2 HRT 2 8 PTU --5 SRT 2 64 PTU
• 3 HRT 3 64 PTU --6 SRT 3 512 PTU
• 7 Non Real Time messages use any available space

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MILCAN Status

• 3 Documents produced
• MILCAN Physical Layer
• MILCAN Data Link Layer
• MILCAN Application Layer
• Message Type table being refined
• Over-the-Bus Identifier Modification under
  consideration

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MILCANStatus

• Established international dialog and
  understanding among suppliers, system integrators
  and users
• As military usage increases, information is
  shared
• Reduces duplication and incompatibilities

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