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3D RoboticsPermalink Reply by Chris Anderson on July 16, 2009 at 12:12pm

It just triggers a field setup process, mostly recording the home GPS in EEPROM. See the System tab in the code for details.

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Permalink Reply by Curt Olson on July 16, 2009 at 12:18pm

The code that references these pins is inside init_ardupilot() so this only has an affect when the unit is initially powered up, right?

Pin 6 is set to HIGH, and the marked as an input pin.

Pin 7 is set to LOW, and then marked as an output pin,

So then if Pin 6 reads LOW, that means the plug is installed, otherwise the plug is not.... Ok, I think I have the general idea.

Question: what is the difference between init_GPS() used when the plug is inserted and fast_init_GPS() which is used when the plug is removed?

Thanks,

Curt.

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3D RoboticsPermalink Reply by Chris Anderson on July 16, 2009 at 12:26pm

I think the first one programs the GPS into binary mode (for EM406 and uBlog); second doesn't have to.

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Permalink Reply by Reto on July 16, 2009 at 1:22pm

fast_init_GPS() is just getting the GPS to a fix with the current configuration and the current stored almanac file:
Excerpt from About.com:GPS:
"If you've ever wondered why your GPS receiver sometimes takes longer to become ready to navigate after it's turned on, it is because it must acquire some basic information in addition to capturing GPS satellite signals.
You may encounter a slow start if your GPS has been unused for days or weeks, or has been transported a significant distance while turned off. In these cases, the GPS must update its almanac and ephemeris data and store it in memory.
The GPS almanac is a set of data that every GPS satellite transmits, and it includes information about the state (health) of the entire GPS satellite constellation, and coarse data on every satellite's orbit. When a GPS receiver has current almanac data in memory, it can acquire satellite signals and determine initial position more quickly."
When the jumper is ON, the GPS is re-programmed by ArduPilot, so the almanac/ephemeris data has to be "downloaded" by the GPS chip before it can get a fix. This take longer and is not necessary if it has a configuration backup, ie if the GPS board has a backup battery. The only problem is that if you want just to store a new Home location in ArduPilot's Eeprom, you will use the jumper (ON) but the GPS will be reprogrammed and fix acquisition waiting is then quite long.
I didn't do it yet, but I think I will change ArduPilot code to have the jumper just to store the new Home in Eeprom, but not to reprogram my GPS, which is working ok without reprogramming (I do not change GPS board brand very often :-)
I even once had the GPS reprogrammed by ArduPilot, but something went bad, and the GPS booted with default settings (57600 bauds) instead of the 34800 I wanted.

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