Trimble Palisade Receiver

Synopsis

`Address:`	127.127.29.u
`Reference ID:`	GPS
`Driver ID:`	GPS_PALISADE
`Serial Port:`	/dev/palisadeu
`Serial I/O:`	9600 baud, 8-bits, 1-stop, odd parity

Description

The refclock_palisade driver supports Trimble Navigation's Palisade Smart Antenna GPS receiver.
Additional software and information about the Palisade GPS is available from: http://www.trimble.com/oem/ntp.
Latest NTP driver source, executables and documentation is maintained at: ftp://ftp.trimble.com/pub/ntp

This documentation describes version 7.12 of the GPS Firmware and version 2.46 (July 15, 1999) and later, of the driver source.

Operating System Compatibility

The Palisade driver has been tested on the following software and hardware platforms:

Platform	Operating System	NTP Sources	Accuracy
i386 (PC)	Linux	NTP Distribution	10 us
i386 (PC)	Windows NT	ftp://ftp.trimble.com/pub/ntp	1 ms
SUN	Solaris 2.x	NTP Distribution	50 us
Hewlett-Packard	HPUX 9, 10, 11	http://us-support.external.hp.com	50 us
Various	Free BSD	NTP Distribution	20 us

GPS Receiver

The Palisade GPS receiver is an 8-channel smart antenna, housing the GPS receiver, antenna and interface in a single unit, and is designed for rooftop deployment in static timing applications.

Palisade generates a PPS synchronized to UTC within +/- 100 ns. The Palisade's external event input with 40 nanosecond resolution is utilized by the Palisade NTP driver for asynchronous precision time transfer.

No user initialization of the receiver is required. This driver is compatible with the following versions of Palisade:

Version	Event Input	Trimble Part Number
7.02	No	26664-00
7.02E	Yes	26664-10
7.12	Yes	38158-00

Note: When using Palisade 26664-00, you must set fudge flag2 to 1 in ntp.conf. See configuration.

GPS Installation

A location with unobstructed view of the horizon is recommended. Palisade is designed to be securely mounted atop standard 3/4 inch threaded pipe.

The 12 conductor (dia. 10 mm) power and I/O cable must be routed from the rooftop site to the NTP server and properly strain relieved.

GPS Connection

The Palisade is equipped with dual (A & B) RS-422 serial interfaces and a differential TTL PPS output. An RS-232 / RS-422 Interface Module is supplied with the Palisade NTP Synchronization Kit. Palisade port A must be connected to the NTP host server. Maximum antenna cable length is 500 meters. See the pinouts table for detailed connection Information.

Palisade's port B provides a TSIP (Trimble Standard Interface Protocol) interface for diagnostics, configuration, and monitoring. Port B and the PPS output are not currently used by the Palisade NTP reference clock driver.

O/S Serial Port Configuration

The driver attempts to open the device /dev/palisadeu where u is the NTP refclock unit number as defined by the LSB of the refclock address. Valid refclock unit numbers are 0 - 3.

The user is expected to provide a symbolic link to an available serial port device. This is typically performed by a command such as:

ln -s /dev/ttyS0 /dev/palisade0

Windows NT does not support symbolic links to device files. COMx: is used by the driver, based on the refclock unit number, where unit 1 corresponds to COM1: and unit 3 corresponds to COM3:

NTP Configuration

Palisade NTP configuration file "ntp.conf" with event polling:
#------------------------------------------------------------------------------
# The Primary reference
server 127.127.29.0 # Trimble Palisade GPS Refclock Unit #0
peer terrapin.csc.ncsu.edu # internet server
# Drift file for expedient re-synchronization after downtime or reboot.
driftfile /etc/ntp.drift
#------------------------------------------------------------------------------

Configuration without event polling:
#------------------------------------------------------------------------------
# The Primary reference
server 127.127.29.0 # Trimble Palisade GPS (Stratum 1).
# Set packet delay
fudge 127.127.29.0 time1 0.020
# and set flag2 to turn off event polling.
fudge 127.127.29.0 flag2 1
#------------------------------------------------------------------------------

Time Transfer and Polling

Time transfer to the NTP host is performed via the Palisade's comprehensive time packet output. The time packets are output once per second, and whenever an event timestamp is requested.

The driver requests an event time stamp at the end of each polling interval, by pulsing the RTS (request to send) line on the serial port. The Palisade GPS responds with a time stamped event packet.

Time stamps are reported by the Palisade with respect to UTC time. The GPS receiver must download UTC offset information from GPS satellites. After an initial UTC download, the receiver will always start with correct UTC offset information.

Run NTP in Debugging Mode

The following procedure is recommended for installing and testing a Palisade NTP driver:

Perform initial checkout procedures. Place the GPS receiver outdoors; with clear view of the sky. Allow the receiver to obtain an UTC almanac.
Verify presence of timing packets by observing the 1 Hz (PPS) led on the interface module. It should flash once per second.
Connect Palisade's port A to the NTP host.
Configure NTP and the serial I/O port on the host system.
Initially use fudge flag2 in ntp.conf, to disable event polling (see configuration).
Run NTP in debug mode (-d -d), to observe Palisade_receive events.
The driver reports the tracking status of the receiver. Make sure it is tracking several satellites.
Remove fudge flag2 and restart ntpd in debug mode to observe palisade_receive events.
If event polling fails, verify the connections and that the host hardware supports RTS control.

Event Logging

System and Event log entries are generated by NTP to report significant system events. Administrators should monitor the system log to observe NTP error messages. Log entries generated by the Palisade NTP reference clock driver will be of the form:

Nov 14 16:16:21 terrapin ntpd[1127]: Palisade #0: message

Fudge Factors

time1 time: Specifies the time offset calibration factor, in seconds and fraction, with default 0.0. If event capture is not used, time1 should be set to 20 milliseconds to correct serial line and operating system delays incurred in capturing time stamps from the synchronous packets.
stratum number: Specifies the driver stratum, in decimal from 0 to 15, with default 0.
refid string: Specifies the driver reference identifier, GPS.
flag2 0 | 1: When set to 1, driver does not use hardware event capture. The synchronous packet output by the receiver at the beginning of each second is time stamped by the driver. If triggering the event pulse fails, the driver falls back to this mode automatically.

DEFINEs

The following constants are defined in the driver source code. These defines may be modified to improve performance or adapt to new operating systems.

Label	Definition	Default Value
DEVICE	The serial port device to be used by the driver	/dev/palisadeu
PRECISION	Accuracy of time transfer	1 microsecond
CURRENT_UTC	Valid GPS - UTC offset	13
SPEED232	Host RS-232 baud rate	B9600
TRMB_MINPOLL	Minimum polling interval	5 (32 seconds)
TRMB_MAXPOLL	Maximum interval between polls	7 (128 seconds)

Data Format

Palisade port A can output two synchronous time packets. The NTP driver can use either packet for synchronization. Packets are formatted as follows:

Packet 8F-AD (Primary NTP Packet)

Byte	Item	Type	Meaning
0	Sub-Packet ID	BYTE	Subcode 0xAD
1 - 2	Event Count	INTEGER	External event count recorded (0 = PPS)
3 - 10	Fractional Second	DOUBLE	Time elapsed in current second (s)
11	Hour	BYTE	Hour (0 - 23)
12	Minute	BYTE	Minute (0 - 59)
13	Second	BYTE	Second (0 - 59; 60 = leap)
14	Day	BYTE	Date (1 - 31)
15	Month	BYTE	Month (1 - 12)
16 - 17	Year	INTEGER	Year (4 digit)
18	Receiver Status	BYTE	Tracking Status
19	UTC Flags	BYTE	Leap Second Flags
20	Reserved	BYTE	Contains 0xFF
21	Reserved	BYTE	Contains 0xFF

Leap Second Flag Definition:
Bit 0: (1) UTC Time is available
Bits 1 - 3: Undefined
Bit 4: (1) Leap Scheduled: Leap second pending asserted by GPS control segment.
Bit 5: (1) Leap Pending: set 24 hours before, until beginning of leap second.
Bit 6: (1) GPS Leap Warning: 6 hours before until 6 hours after leap event
Bit 7: (1) Leap In Progress. Only set during the leap second.
Tracking Status Flag Definitions:

Code	Meaning	Accuracy	Receiver Mode
0	Receiver is Navigating	+/- 1 us	Self Survey
1	Static 1 Sat. Timing Mode	+/- 1 us	1-D Timing
2	Approximate Time	20 - 50 ms	Acquisition
3	Startup	N/A	Initialization
4	Startup	N/A	Initialization
5	Dilution of Position too High	5 ppm	Self Survey
6	Static 1 Sat. Timing: Sat. not usable	5 ppm	1-D Timing
7	No Satellites Usable	N/A	Self Survey
8	Only 1 Satellite Usable	20 - 50 ms	Self Survey
9	Only 2 Satellite Usable	20 - 50 ms	Self Survey
10	Only 3 Satellites Usable	20 - 50 ms	Self Survey
11	Invalid Solution	N/A	Error
12	Differential Corrections	N/A	N/A
13	Overdetermined Fixes	+/- 100 ns	Timing Steady State

Packet 8F-0B (Comprehensive Timing Packet)

Byte	Item	Type	Meaning
0	Sub-Packet ID	BYTE	Subcode 0x0B
1 - 2	Event Count	INTEGER	External event count recorded (0 = PPS)
3 - 10	UTC / GPS TOW	DOUBLE	UTC / GPS time of week (seconds)
11	Date	BYTE	Day of Month
12	Month	BYTE	Month of Event
13 - 14	Year	INT	Year of event
15	Receiver Mode	BYTE	Receiver operating dimensions: 0: Horizontal (2D) 1: Full Position (3D) 2: Single Satellite (0D) 3: Automatic (2D / 3D) 4: DGPS reference 5: Clock hold (2D) 6: Over determined Clock
15 - 17	UTC Offset	INTEGER	UTC Offset value (seconds)
18 - 25	Oscillator Bias	DOUBLE	Oscillator BIAS (meters)
26 - 33	Oscillator Drift Rate	DOUBLE	Oscillator Drift (meters / second)
34 - 37	Bias Uncertainty	SINGLE	Oscillator bias uncertainty (meters)
38 - 41	Drift Uncertainty	SINGLE	Oscillator bias rate uncertainty (m / sec)
42 - 49	Latitude	DOUBLE	Latitude in radians
50 - 57	Longitude	DOUBLE	Longitude in radians
58 - 65	Altitude	DOUBLE	Altitude above mean sea level, in meters
66 - 73	Satellite ID	BYTE	SV Id No. of tracked satellites

Pinouts

The following connections are required when connecting Palisade with a host:

Description	Host			Palisade
Port A	DB-9	DB-25		RS-232	RS-422	Palisade Pin
Receive Data	2	3	<-->	Green	Green / Blue	8 (T-) & 10 (T+)
Request to Send	7	4	<-->	Gray	Gray / White	6 (R-) & 7 (R+)
Signal Ground	5	7	<-->	Black	Black	9 (GND)

Port B
Receive Data	2	3	<-->	Brown	Brown / Yellow	4 (T-) & 5 (T+)
Transmit Data	3	2	<-->	Violet	Orange/ Violet	2 (R-) & 3 (R+)
Signal Ground	5	7	<-->	Black	Black	9 (GND)

Note: If driving the RS-422 inputs on the Palisade single ended, i.e. using the Green and Gray connections only, does not work on all serial ports. Use of the Palisade NTP Synchronization Interface Module is recommended.

The 12 pin connector pinout definition:
Face the round 12 pin connector at the end of the cable, with the notch turned upwards.
Pin 1 is to the left of the notch. Pins 2 - 8 wrap around the bottom, counterclockwise to pin 9 on the right of the notch. Pin 10 is just below the notch. Pins 10 (top), 11 (bottom left) and 12 (bottom right) form a triangle in the center of the connector.

Pinouts for the Palisade NTP host adapter (Trimble PN 37070) DB-25 M connector are as follows:

DB-25M	Conductor	Palisade	Description
1	Red	1	Power
7	Black	9	Ground
9	Black/White	12	PPS -
10	Green	8	Transmit Port A (T-)
11	Brown	4	Transmit Port B (T-)
12	Gray	7	Receive Port A (R+)
13	Orange	3	Receive Port B (R+)
21	Orange/White	11	PPS +
22	Blue	10	Transmit Port A (T+)
23	Yellow	5	Transmit Port B (T+)
24	White	6	Receive Port A (R-)
25	Violet	2	Receive Port B (R-)

Questions or Comments:
Sven Dietrich
Trimble Navigation Ltd.

(last updated July 29, 1999)