BCM4751 » History » Revision 4
Revision 3 (Paul Kocialkowski, 02/17/2012 10:55 AM) → Revision 4/33 (Paul Kocialkowski, 02/17/2012 10:56 AM)
h1. Broadcom4751GPS
h2. Files
The non-free files holding the GPS infos/code are the following:
<pre>
/system/vendor/bin/gpsd
/system/vendor/lib/hw/gps.s5pc110.so
/system/vendor/etc/gps.xml
/system/etc/gps.conf
</pre>
h2. Protocol
Apparently, the protocol that is used by the chip to provide the GPS infos is MEIF. The GPSD component is in charge of translating that to standard NMEA that is sent to the gps.s5pc110.so lib via the /dev/socket/gps Unix socket, created by GPSD.
h2. Attempts
We have written code to read data from the correct serial interface: https://gitorious.org/replicant/crespo-gps-utils
It currently doesn't work: it fails to somehow boot the chip. Though, it works after starting gpsd once and stopping it. It must be doing some kind of magic code to start the chip.
h3. Related gps.xml parameters
We have tried to change some parameters in gps.xml to see how it behaves:
|_. Parameter |_. Original |_. Changed to |_. Result |
| acPortName | /dev/s3c2410_serial1 | /dev/s3c2410_serial42 | The chip wasn't "booted" |
| gpioNStdbyPath | /sys/class/sec/gps/GPS_PWR_EN/value | /sys/class/sec/gps/GPS_PWR_EN/value2 | The chip was booted |
| gpioNResetPath | /sys/class/sec/gps/GPS_nRST/value | /sys/class/sec/gps/GPS_nRST/value2 | The chip was booted |
After all, it seems that when the gpsd binary is running without the gps.s5pc110.so library, the chip isn't started (our test utility doesn't work) whereas when the library is running and connects to the socket when it is created by starting gpsd, the chip is booted. The init code is probably in gps.s5pc110.so then.
Things to try:
* intercept what is going on through the /dev/socket/gps socket
* emulate gpsd to the lib