GPS授时服务器DIY

国内外厂商制造的高精度时钟服务器实际都是基于x86服务器,加装铷钟和GPS接收模块构成。树莓派流行起来后,网上也有配套的模块,让大家可以制造一个小巧的时钟服务器。实际这淘宝上有很多USB接口的GPS接收模块,产品特性:
GPS+GLONASS双模定位
内置FLASH,USB供电
自适应1200-921600波特率
1Hz输出,NMEA-0183协议输出。
NTPD是业内对各种GPS接受器支持的最好的,绝大部分GPS接受模块实际都是使用标准的NMEA协议从/dev/gps输出。

测试的配置如下:

# For more information about this file, see the man pages
# ntp.conf(5), ntp_acc(5), ntp_auth(5), ntp_clock(5), ntp_misc(5), ntp_mon(5).
logfile /var/log/ntp.log
driftfile /var/lib/ntp/drift
# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
restrict default nomodify notrap nopeer noquery

# Permit all access over the loopback interface.  This could
# be tightened as well, but to do so would effect some of
# the administrative functions.
restrict 127.0.0.1
restrict ::1

# Hosts on local network are less restricted.
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap

# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
server 127.127.20.1 mode 17 minpoll 4 maxpoll 4
fudge  127.127.20.1 stratum 0 refid GPS  flag1 1 flag2 0 flag3 1
server 127.127.1.1 minpoll 4 maxpoll 4
fudge  127.127.1.1 stratum 1 refid LCK
#

# Enable public key cryptography.
#crypto

includefile /etc/ntp/crypto/pw

# Key file containing the keys and key identifiers used when operating
# with symmetric key cryptography.
keys /etc/ntp/keys

# Specify the key identifiers which are trusted.
#trustedkey 4 8 42

# Specify the key identifier to use with the ntpdc utility.
#requestkey 8

# Specify the key identifier to use with the ntpq utility.
#controlkey 8

# Enable writing of statistics records.
#statistics clockstats cryptostats loopstats peerstats

# Disable the monitoring facility to prevent amplification attacks using ntpdc
# monlist command when default restrict does not include the noquery flag. See
# CVE-2013-5211 for more details.
# Note: Monitoring will not be disabled with the limited restriction flag.
disable monitor
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