20150414_DARPA-BAA-15-33_Attachment_3_NGIMU_ICD.pdf

INTERFACE CONTROL DOCUMENT (ICD)

Prepared for

PRECISE ROBUST INERTIAL GUIDANCE FOR MUNITIONS:

NAVIGATION-GRADE INERTIAL MEASUREMENT UNIT

(PRIGM:NGIMU)

April 10, 2015

Prepared by:

Defense Advanced Research Projects Agency (DARPA) Microsystems Technology Office (MTO)

U.S. Army AMRDEC Redstone Arsenal, AL

DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE;

DISTRIBUTION IS UNLIMITED.

RECORD OF REVISIONS

Rev Result of Pages Affected Approval/Date

TABLE OF CONTENTS

Section Page

1 SCOPE 5

1.1 IDENTIFICATION 5

1.2 SYSTEM OVERVIEW 5

1.3 DOCUMENT OVERVIEW 5

2 REFERENCED DOCUMENTS 6

2.1 GOVERNMENT DOCUMENTS 6

2.2 NON-GOVERNMENT DOCUMENTS 6

2.3 ORDER OF PRECEDENCE 6

3 REQUIREMENTS 7

3.1 MECHANICAL INTERFACES 7

3.1.1 Outline Dimensions 7

3.1.2 Sense Axis 7

3.2 PHYSICAL 7

3.2.1 Weight 7

3.2.2 Volume 7

3.3 ELECTRICAL INTERFACE 8

3.3.1 Interface Signals 8

3.3.2 Grounding 8

3.4 MISSION COMPUTER / IMU INTERFACE 8

3.4.1 Receive Clock 9

3.4.2 Serial Data Output 9

3.4.3 Initiated BIT Input Discrete (IBIT) 9

3.4.4 Reset Input Discrete 9

3.4.5 Output Disable 10

3.4.6 Serial Data Output Protocols 10

3.4.6.1 Serial Communications Interface 10

3.4.6.1.1 SDLC Point-to-Point Protocol 10

3.4.6.1.1.1 SDLC Point-to-Point 1200 Hz Control / 200 Hz Guidance Message Format 11

3.4.6.1.1.2 Data Latency 14

3.5 POWER UNIT / IMU INTERFACE 14

3.5.1 Input Power 14

3.5.2 Power Sequence 14

3.5.3 Isolation 14

3.5.4 Characteristics 14

4 QUALIFICATION PROVISIONS 16

4.1 REQUIREMENTS VERIFICATION 16

5 NOTES 17

5.1 ACRONYMS 17

LIST OF FIGURES

Figure Page

FIGURE 1: IMU CONCEPTUAL DRAWING 7

FIGURE 2: SDLC MESSAGE 10

LIST OF TABLES

Table Page

TABLE 1 - GOVERNMENT DOCUMENTS 6

TABLE 2 - NON-GOVERNMENT DOCUMENTS 6

TABLE 3 - IMU J1 CONNECTOR 8

TABLE 4 - SDLC BUS CHARACTERISTICS 11

TABLE 5 - IMU MESSAGE ID 11

TABLE 6 - CONTROL MESSAGE INFORMATION FIELD CONTENTS (MESSAGE ID 1) 12

TABLE 7 - CONTROL/GUIDANCE MESSAGE INFORMATION FIELD CONTENTS (MESSAGE ID 2) 12

TABLE 8 - SDLC CONTROL MESSAGE INFORMATION FIELD MAIN STATUS WORD 13

TABLE 9 - SDLC CONTROL MESSAGE INFORMATION DETAILED MULTIPLEXED STATUS WORDS 13

TABLE 10 - INPUT POWER REQUIREMENTS 14

TABLE 11 - IN-RUSH CURRENT 15

1 SCOPE

1.1 Identification

This document specifies the baseline IMU interface requirements for the PRIGM:NGIMU program.

1.2 System Overview

The NGIMU will be a low-CSWaP, navigation-grade, gun-hardened, MEMS-based IMU. The focus of this effort is to develop a MEMS IMU that sustains GPS-quality navigation accuracy for up to 180 seconds in a GPS-denied theater. At the end of the program, contractors shall deliver 10 MEMS-based navigation-grade IMU prototypes to Service Labs for relevant demonstrations.

1.3 Document Overview

This document defines electrical, logical and physical interface requirements between the IMU and the Mission Computer (MC), Power Conditioning Unit (PCU) and the mechanical interface to the munition platform. Interface requirements are detailed in section 3, and qualification provisions are detailed in section 4.

This document and accompanying system specifications will be refined throughout the program, based on inputs from government personnel and performers.

This document is unclassified.

2 REFERENCED DOCUMENTS

The documents listed in this section are referenced in sections 3 and 4 of this document. This section does not include documents cited in other sections of this document or recommended for additional information or as examples. While every effort has been made to ensure the completeness of this list, document users are cautioned that they must meet all specified requirement documents cited in section 3 and 4 of this specification, whether or not they are listed.

2.1 Government Documents

The Government specifications, standards, and/or handbooks identified in Table 1 form a part of this document to the extent specified herein. Unless otherwise specified, the issue of MIL-STD- 498 is that listed in the issue of the Department of Defense Index of Specifications and Standards (DoDISS) and supplement thereto, cited in the solicitation. (Unless otherwise indicated, copies of the below specifications, standards, and handbooks are available from the Standardization Document Order Desk, 700 Robbins Avenue, Building 4D, Philadelphia, PA 19111-5094).

Unless otherwise stated, the latest version of the document will be used.

Table 1 - Government Documents

Document Number Title MIL-STD-498 Software Development and Documentation

CG IMU ICD

#321825

Common Guidance Interface Control Document Broad Agency Announcement Number

DAAE30-01-BAA-0101

(U.S. Army ARDEC, AMRDEC)

2.2 Non-Government Documents

The non-government document in Table 2 form a part of this document to the extent specified herein. Unless otherwise stated the latest version of the document will be used.

Table 2 - Non-Government Documents

Document Number Title EIA RS-485 Standard for Electrical Characteristics of Generators and

Receivers for use in Balanced Digital Multiport Systems

2.3 Order of Precedence

In the event of a conflict between the text of this document and the references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained.

3 REQUIREMENTS

3.1 Mechanical Interfaces

3.1.1 Outline Dimensions

Conceptual drawing of the NGIMU is shown in Figure 1. The NGIMU shall meet the outline dimensions and configuration as defined in DARPA-BAA-15-33 Attachment 4.

Figure 1: NGIMU Conceptual Drawing

3.1.2 Sense Axis

The IMU shall provide three-axis angular rate and linear acceleration and three-axis incremental angle and incremental velocity.

The X-axis shall coincide with the centerline of the IMU.

The Y-axis shall be coincident with the line that bisects the center of the two mounting holes closest to the external connector.

The Z-axis shall be defined by the right hand rule with the X and Y-axes.

3.2 Physical

3.2.1 Weight

The weight of the IMU shall be ≤ 160 g.

The weight of the IMU, once established, shall not vary by more than +/-5%.

3.2.2 Volume

The volume of the IMU shall be 82 cm3, including mounting feet.

Z

Y

X

3.3 Electrical Interface

3.3.1 Interface Signals

The IMU shall provide the external interfaces signals on the IMU external connector, J1, as defined in Table 3.

Table 3 - IMU J1 Connector

Pin Tactical Connection

Name I/O Type

1 Return PCU_RTN I Return 2 +5V PCUP5VDC I Power 3 None RESERVE I Test Connection 4 None IMU2TC O Test Connection

RS-232 output 5 Return TC2IMU I Test Connection

RS-232 input 6 Signal IMU_Reset I CMOS 7 Signal IMU_SIM_DATA_ENABLE~ I CMOS 8 Signal BIT_ENABLE~ I CMOS 9 Signal IMU_DATA+ O RS-422/485

10 Signal IMU_DATA- O RS-422/485 11 Signal RESERVE I/O RS-422/485 12 Signal RESERVE I/O RS-422/485 13 Signal DCLK+ I RS-422/485 14 Signal DCLK- I RS-422/485

3.3.2 Grounding

The IMU electronics shall be electrically isolated from the IMU housing.

The IMU shall use the signal, PCU_RTN, found on the external connector, as the reference for all other input/output signals.

The IMU shall provide for the following external grounding connections via external screws/lugs as defined in the Outline Dimension drawing shown above:

1) Chassis ground

2) Cable shield

3.4 Mission Computer / IMU Interface

This interface provides the following functionality:

A power-up/initiated Built-In-Test (BIT) capability provides the navigation section with the ability for commanding BIT and receiving BIT status data from the IMU.

A reset capability provides the navigation section with the ability to reset the IMU to its power-up state.

An Interface Disable capability provides the navigation section with the ability to disable the IMU interface.

A data interchange capability provides the navigation section with the ability for obtaining the following IMU data via the Serial Output Data interface:

BIT Status Data is output as requested.

3.4.1 Receive Clock

The hardware shall accept a continuous RS-422 compatible clock signal on the DCLK+ and DCLK- pins of the IMU external interface connector as specified in Table 3 IMU J1 Connector.

The SDLC transmit clock frequency shall have a nominal 50% duty cycle.

Only a single clock rate shall be used during operation and the clock rate shall be constant during operation.

3.4.2 Serial Data Output

The IMU’s hardware / software shall provide a single RS-422 compatible serial data output for interface.

The serial data output shall be the IMU_DATA+ and IMU_DATA- pins of the IMU external interface connector as specified in Table 3.

The serial data output shall be synchronous with the receive clock as described in Section 3.4.1.

Serial data output shall be shifted on the falling edge and valid on the rising edge of the clock.

3.4.3 Initiated BIT Input Discrete (IBIT)

The system shall accept a 5 VDC CMOS compatible discrete input for Initiated Built-In-Test (IBIT) on the BIT_ENABLE~ pin of the IMU external interface connector as specified in Table 3.

The IBIT Input Discrete signal shall be internally pulled to a logical 1 to allow a no connect, or open, at the system level.

The IMU shall enter IBIT Mode when the BIT_ENABLE~ discrete is held active low, logical 0, for at least 7 msec. When asserted, the BIT_ENABLE~ discrete shall be asserted for not less than 200 milliseconds.

3.4.4 Reset Input Discrete

The IMU hardware shall also be capable of initiating a reset independent of the state of the reset input discrete.

The application of logic 1 on the IMU_Reset input, for a minimum of 7 milliseconds, shall cause the IMU to halt all processes. The IMU shall remain halted for the duration of logic 1 on the IMU_Reset input. Upon restoration of logic 0, or open, on the IMU_Reset input, the IMU shall then restart the power-up initialization process and transition to normal operation.

The IMU_Reset input discrete signal shall be internally pulled to a logic 0 to allow a no connect, or open at the system level.

The under voltage reset shall hold the reset input discrete in the low state for a minimum of 20 milliseconds.

3.4.5 Output Disable

The output disable input discrete IMU_SIM_DATA_ENABLE~ shall be internally pulled to a logical 1 to allow a no connect at the system level as specified in Table 3.

The system shall disable (tri-state) the RS-422 driver when the IMU_SIM_DATA_ENABLE~ is a logical 0.

3.4.6 Serial Data Output Protocols

The IMU shall support the SDLC protocol.

3.4.6.1 Serial Communications Interface

The serial data output/input shall be RS-422 compatible.

3.4.6.1.1 SDLC Point-to-Point Protocol

The two byte Cyclic Redundant Check (CRC) shall follow the data message. The CRC shall be calculated using the CCITT polynomial X 16 +X 12 +X 5 +1, preset to ones.

Each Synchronous Data Link Control (SDLC) output frame shall open with a flag followed by the information that includes address, control and data fields.

An ending flag shall follow the CRC and ending flags are transmitted continuously between frames.

The format for the SDLC message is shown in Figure 2.

Frame Check 16 Bits

Information Any Number of Bits

Address 8 Bits

Control 8 Bits

Ending Flag 01111110

8 Bits

Beginning Flag 01111110

8 Bits

Frame

Data

1x Clock

Figure 2: SDLC Message

The order of transmission is Least Significant (LS) bit first; LS byte first; LS 16 bit word first.

The address field shall contain a unique hex number to identify the IMU model and the control field shall contain the message ID.

The information field generated by the software shall include the parameters as specified in the following sections for each message format.

The SDLC bus characteristics shall be as shown in Table 4.

Table 4 - SDLC Bus Characteristics Parameter Description Shift Clock Programmable

Input Data Encoding NRZ (Non-

Return to Zero) SDLC Mode Point-to-Point

CRC CCITT

Data Ordering Least

Significant (LS) bit first; LS byte first; LS 16 bit word first Message Format

Message from host to IMU

Message from IMU to Host

NONE USED Description Bytes Value/Para Flag 1 7Eh IMU Addr 1 Per user

Requirement IMU Msg ID 1 01h = Control

Data;

02h = Control and Guidance data Data As specified in

Tables 3 and 4

CRC 2

Flag 1 7Eh

3.4.6.1.1.1 SDLC Point-to-Point 1200 Hz Control / 200 Hz Guidance Message Format The IMU shall send the information message fields listed in Table 6 and Table 7.

The control field shall contain the message ID as shown in Table 5.

The start of the sequential transmissions of the message ID number 1 shall be on the average 1/1200 seconds +/- 0.01% apart.

The start of the sequential transmissions of the message ID number 2 shall be on the average 1/200 seconds +/- 0.01% apart.

Table 5 - IMU message ID IMU Message ID Title Source Destination

1 Control Data IMU System Processor 2 Control and Guidance

Data IMU System Processor

Table 6 - Control Message Information Field Contents (Message ID 1) SDLC Control Message Information Field

Word Parameter Bytes Format LSB Scaling Units/Value 1 Angular Rate X (Roll) 2 2’s comp 2-20 * 1200 Rad/sec/LSB 2 Angular Rate Y (Body) 2 2’s comp 2-20 * 1200 Rad/sec/LSB 3 Angular Rate Z (Body) 2 2’s comp 2-20 * 1200 Rad/sec/LSB 4 Linear Acceleration X

(Body) 2 2’s comp 2-14 * 1200 ft/sec2/LSB

5 Linear Acceleration Y (Body)

2 2’s comp 2-14 * 1200 ft/sec2/LSB

6 Linear Acceleration Z (Body)

2 2’s comp 2-14 * 1200 ft/sec2/LSB

7 Main Status Word 2 binary N/A See Table 8 – SDLC Control

Message Information Field

Main Status Word

8 Detailed Status Word (Multiplexed)

2 binary

N/A See Table 9 – SDLC Control

Message Information Field

Detailed Multiplexd

Status Word Total 16

Gyro body axes output range > ± 1440 deg/sec or ± 7200 deg/sec for 4 Hz

Accel body axes output range > ± 70g

Detailed status word alternates at the control message rate as indicated by the Detailed Multiplexed Status Word Counter of the Main status word See Table 5.

Table 7 - Control/Guidance Message Information Field Contents (Message ID 2) SDLC Control/Guidance Message Information Field

Item Parameter Bytes Format LSB Scaling Units/Value 1-8 Control Data same as message ID 1

9 ∆θx 4 2’s comp 2-33 radians/LSB 10 ∆θy 4 2’s comp 2-33 radians/LSB 11 ∆θz 4 2’s comp 2-33 radians/LSB 12 ∆Vx 4 2’s comp 2-27 Ft/sec/LSB 13 ∆Vy 4 2’s comp 2-27 ft/sec/LSB 14 ∆Vz 4 2’s comp 2-27 ft/sec/LSB

Total 40

Gyro body axes output range > ± 1440 deg/sec or ± 7200 deg/sec for 4 Hz

Accel body axes output range > ± 70g

Table 8 - SDLC Control Message Information Field Main Status Word Bit Order Parameter Definition 15 (MSB) Operating Mode 0=Normal Operation, 1=BIT

14 CBIT Status 0=OK, 1=Failed 13 PBIT Status 0=OK, 1=Failed 12 IBIT Status 0=OK, 1=Failed 11 Gyro X Validity 0=OK, 1=Failed 10 Gyro Y Validity 0=OK, 1=Failed 9 Gyro Z Validity 0=OK, 1=Failed 8 Accelerometer X Validity 0=OK, 1=Failed 7 Accelerometer Y Validity 0=OK, 1=Failed 6 Accelerometer Z Validity 0=OK, 1=Failed 5 Spare 4 Spare

3-0 Detailed Multiplexed Status Word Counter

Value increments each message transmission, counting from 0 to 15 and repeating. Value indicates content of Detailed Status Word in bytes 3-4 of current message.

Table 9 - SDLC Control Message Information Detailed Multiplexed Status Words Mux Word Counter

Contents Units Format LSB Scaling

Mux word 0 Software Version Number * Binary Coded N/A Mux word 1 Detailed BIT Status Word 1 * Binary Coded N/A Mux word 2 Detailed BIT Status Word 2 * Binary Coded N/A Mux word 3 Detailed BIT Status Word 3 * Binary Coded N/A Mux word 4 Detailed BIT Status Word 4 * Binary Coded N/A Mux word 5 Detailed BIT Status Word 5 * Binary Coded N/A Mux word 6 Temperature 1 * Deg C 2’s comp 0.0039

Mux word 7 Spare * Mux word 8 Spare** Mux word 9 Spare**

Mux word 10 Spare** Mux word 11 Spare** Mux word 12 Spare** Mux word 13 Spare** Mux word 14 Spare** Mux word 15 Spare**

* These words shall be defined by the manufacturer ** These words are available for the User to specify.

3.4.6.1.1.2 Data Latency

Data latency shall be defined as the elapsed time from the sampling of the last data sample until the end of transmission of the output message containing the information. This latency shall be further decomposed into computation delay and transport delay, and gain and phase response of various filters. Computational delay for the IMU shall be less than 400 µs and shall be measured from the data sample point to the point at which data is presented to the transmit controller.

Transport delay for the IMU shall be less than 211 µS for the control message and be less than 441 µS for the guidance/control message. It shall be measured from the point at which data is strobed into the transmit controller until the closing flag of the message has been transmitted. For the latter characteristic, the bit clock shall be assumed to be 1 MHz.

3.5 Power Unit / IMU Interface

3.5.1 Input Power

The IMU shall meet the performance requirements of this specification when supplied with input power as shown in Table 11.

The IMU shall be capable of providing accurate angular rate, linear acceleration, delta angle and delta velocity data as specified herein within 1.0 second after application of input power and de-assertion of the IMU reset signal in accordance with 3.3.1.

3.5.2 Power Sequence

The IMU shall function in accordance with this specification when input power forms are applied in any sequence. Absence of any one or more of the required power supplies shall not cause permanent damage to the IMU.

3.5.3 Isolation

The isolation resistance of all input power forms to chassis ground shall be greater than 1 Megaohms.

The isolation resistance between the +5 Volt Power Return and chassis ground shall be greater than 10K ohms.

3.5.4 Characteristics

Power requirements are specified in Table 10. NOTE: Maximum current draw is highly dependent on the rise time of the power supplies. The values listed in the table are valid only for supplies where rise times are 2mS or longer. For shorter rise times, current shall be calculated using actual rise times that will be present in the application.

The maximum in-rush current is specified in Table 11.

Table 10 - Input Power Requirements

Voltage (VDC)

Tolerance Maximum

Ripple (mV p-p)

Max Run Current (Amp)

+5 ±5% 50 1.0

Note: The run current requirement does not include the transient current required to charge the IMU internal distributed capacitance on the +5 volt power input. See Table 11

Table 11 - In-rush Current

Voltage

(VDC)

Tolerance

Max In-rush Current (Amp)

Time Duration <2msec

+5 ±5% 3

Note: In-rush current is for 5 volt power supply voltage rise time > 2msec.

4 QUALIFICATION PROVISIONS

4.1 Requirements Verification

Verification that the IMU meets the requirements of section 3 shall be determined by one of the following methods as designated below.

Inspection (I) - Physical examination of documentation, hardware or software to verify conformance to specified requirements. Inspection is used to check adequacy of design documentation to applicable specifications and conformance of hardware and software to design documentation and applicable standards. Inspection includes verification by design reviews and evaluation of the engineering design.

Analysis (A) - The use of recognized techniques, including computer models to interpret or explain equipment performance or test data. Analysis is used in lieu of, or to supplement, test data.

Demonstration (D) - Performance of the actual function of the design requirement.

Demonstration is used when quantitative measurement is not required for verification.

Test (T) - To provide data in an operational environment. The data are subsequently used to evaluate quantitative product performance and effectiveness characteristics. Evaluation includes comparison of demonstrated characteristics with requirements.

5 NOTES

5.1 Acronyms

BIT Built-In Test CCA Circuit Card Assembly CRC Cyclic Redundant Check DoD Department of Defense DoDISS Department of Defense Index of Specifications and Standards IBIT Initiated BIT ICD Interface Control Document IMU Inertial Measurement Unit ISA Inertial Sensor Assembly LS Least Significant MC Mission Computer MEMS MicroElectroMechanical System NGIMU Navigation-Grade Inertial Measurement Unit PCU Power Conditioning Unit SDLC Synchronous Data Link Control