My plan today is to work some more on the GPS startup. I am wondering if the problem might be that the position data in the POSHOLD command is not sufficiently accurate? A better procedure (suggested in the manual) might be to average position data over a period of time before initiating POSHOLD mode. This would also be helpful when installing the system at a new site location (or in general when moving the GPS antenna).
Also, I can still try the strategy of querying the current NTP time from the server to initialize the time to ~10 ms resolution. However, even just 10 ms of time uncertainty equates to 3,000 km of position uncertainty, so I'm not sure how useful it will be to set the time more accurately.
Anyway, let's try to get this thing up and running again. I'm going to carefully log all my steps to facilitate a postmortem next time the GPS fails to connect.
- (2:31 pm) My immediate plan is to first connect through UwTerminal, then select the default configuration, access the kit using the demo software, and then wait 15 min. or so to re-acquire satellites.
- (2:32 pm) The current configuration is: Batteries not installed. USB not plugged in. AC adapter not plugged in. NMEA port connected to COM1 via gender bender. NMEA port switch in rightwards ("DCE") position. Power switch in leftwards ("on") position.
- (2:33 pm) Starting UwTerminal. Setting COM=1, baudrate=57,600, handshaking=none. Click OK. No data of course because the kit isn't powered on yet.
- (2:35 pm) Now I'll plug in the AC adapter for power. The unit confirms:
- (2:38 pm) Unplugged unit a few minutes ago to stop text from scrolling so I could note the above. Now plugging it in again to see if it acquires anything. I don't think it will.
- (2:40 pm) Going to send an NMEA-off command to make it easier to send other commands. Download-->Stream File Out-->NMEA-off.txt. No response. I think the last time this happened, I decided it was a grounding problem. Going to switch temporarily to the batteries for power supply.
- (2:41 pm) Inserted batteries (two AAs).
- (2:42 pm) Unplugging AC adapter. Power light goes off (this is normal for battery mode), but status light still flashing red. Now trying to send the file again. Still no response! Wait, maybe in battery mode the level shifter is disabled? Doesn't look like it from a quick glance at schematic... Anyway, let's try the USB power supply now.
- (2:44 pm) Plugging in USB cord, unplugging battery. Now the NMEA-off command works.
- (2:45 pm) Wondering if, before I revert to the demo app, I should first try the POSHOLD and TRAIM commands, with the correct time value in the POSHOLD. Or actually, first, try the $PDME,9 command to just initialize the position and time. "Must be issued immediately after a reset or startup to be most effective." OK, so first, power off the unit. Unplugging USB.
- (2:47 pm) Starting SciTE, opening "C:\Users\Mike\Documents\My Dropbox\FAMU\COSMICi\GPS FPGA app\NMEA command files\init-pos.txt", preparing to write new contents. Old contents:
- $PDME,9,30.428236,-84.285,40,2011,11,22,21,47,30
- (2:49 pm) All I have to do, I think, is update the time value to something semi-accurate. Let's go to time.gov and make sure we know the correct UTC(GMT) time. It is 19:50. So, allowing a minute or so to start, let's write:
- $PDME,9,30.428236,-84.285,40,2011,11,28,19,52,00
- (2:52 pm) OK, sent that line right after plugging in the unit's power. Looks like I was about 15 seconds early (compared to what the real time was), but at least it's close enough to help it find the satellites, hopefully. Next step: Just wait 15 minutes or so to acquire satellites, hopefully.
- (2:55 pm) An observation: The $PDMETRAIM line is reporting condition 2 (unknown), and the LED D9 is flashing green once every 2 seconds. I don't know what this means! (That signal TRACKLED connected to the green is supposed to mean "3D fix" but I don't know what it means for it to flash once every 2 seconds - undocumented behavior?)
- (2:58 pm) Checking the scope; there is no PPS edge currently (consistent with no time lock). Still no satellites showing.
- (3:01 pm) OK, I'm still getting no sign of any satellites. I think I'd better abort this test for now. Sending NMEA-off.txt.
- (3:02 pm) Now sending select-default.txt.
- (3:03 pm) Now sending hot-start.txt. Switching UwTerminal baud rate to 4800 to match. I wonder if just doing this (switching back to default config) will help acquisition at all? Maybe wait a little while to see.
- (3:06 pm) Still no satellites. Wait a few more minutes and then try the demo app.
I should test again to see if it works without the USB blaster (JTAG) cable. Yep, it does.
Here is a pic of the setup showing no cables but power and GPS antenna cable:
Here is a screenshot of the server windows:
And here is a closeup of the main output window:
Guess I'll have to recreate all those setup notes some other time...
Here is a screenshot showing both the output from the the CTU (DE3 board GPS app) and the FEDM simultaneously:
What next? Maybe, try putting the GPS in standby when on battery power? I think I'll do that when I leave today.
One more thing: I averaged the coordinates from the GPGGA lines from the latest run, about an hour's worth (4:55 - 5:55 pm). Here is the averaged data:
- Latitude: 30 degrees, 25.65445 minutes, sample standard deviation 0.01596 minutes (29.56 m).
- Longitude: 84 degrees (W), 17.11387 min., sample std. dev. 0.00881 minutes (~14 m).
- Altitude: 62.81 m, sample std. dev. 21.50 m
Also on Google Earth. Is the signal reflecting off the building, or what? Don't know...
OK, 6:22 pm - STOP, exit on FEDM; MUTE, STOP, exit on DE3; DE3 power off; switching GPS switch to OFF/STANDBY position. Tomorrow we'll see how hard it is to re-acquire the signal...
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