I finally found a solution.
This article was very usefull for me
http://spellfoundry.com/2016/05/29/configuring-gpio-serial-port-raspbian-jessie-including-pi-3/#comment-67160
and i recommand you to read it
Now on RPI3 the Serial port
So :
after a reinstallation of Jessie with a recent version to be sure all is clean
as usual
$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo raspi-config
go to Advanced options :
Would you like a login shell to be accessible over serial?
response "yes" (not as in the microstack datasheet )
$ sudo apt-get install python3-microstacknode
To install the gpsd standard tools
$ sudo apt-get install gpsd gpsd-clients python-gps
edit GPSD by
$ sudo nano /etc/default/gpsd
and put the options :
START_DAEMON="true"
USBAUTO="false"
DEVICES="/dev/serial0"
GPSD_OPTIONS="-n -G"
equally
$ sudo nano /boot/cmdline.txt
remove
console=serial0,115200
and save
$ sudo nano /boot/config.txt
you must have at the end
enable_uart=1
Disable the console by
$ sudo systemctl stop [email protected]
$ sudo systemctl disable [email protected]
i have equally done
$ sudo chmod 775 ../../dev/ttySO
( i dont know if it is really necessary )
and obviously a reboot
and miracle the gps works with
cgps -s
NB: you must have a fix on the GPS ( the red led flashes )