xv6800+GPS搜不到星，各位大侠，请指点，多谢！

现在的device information:
ROM version: dcd 4.1.2
ROM date: 1/21/09
Radio version:3.37.78
Protocol version: DCAAXOM-4350H
Hardware version: 0003
PRL version: 50949
PRI version: 2.03_002

GPS program port : COM4
GPS hardware port:None
Baud rate: 4800
Manage GPS automatically

Location Setting: ON

装了个Google Maps, GPS setting: Managed by Windows/COM4:/4800
在停车场里，大晴天，搜了二三十分钟，还是0

可能出错的环节在哪里？
多谢