On Jun 3, 2015 7:44 AM, "Kenny" <ke...@romhat.net> wrote: > + The STM32 which controls the MAX2769 (GPS baseband receiver) now > dynamically configures the MAX according to instructions received by > debug scripts so we can test all the configurations we want without > reprogramming the STM32 each time.
I was skeptical about whether this would be worth the engineering effort, but Theo's time spent building it already paid for itself last night. Excellent idea. > + Kenny joined the party to help transmit a sweeping sine wave +/- > 2MHz around GPS baseband using HackRF. Samples received from the > MAX2769, converted and viewed in baudline showed the same sweeping sine > wave (with noise and other artifacts). This turned out to be a good way > to test poorly documented configuration settings and lay to rest > bit-order questions. I disagree. It was a *great* way to test. ;-) We now have confidence about the meaning of most of the MAX2769 registers, and we know the entire signal path on the jGPSv3 board is functioning! I have two next steps in mind for testing: First, someone (Nathan or me probably) should generate one GPS satellite's pseudonoise sequence in a file. We should test feeding it into soft-correlator first, which ought to report a strong signal from that satellite at 0 Doppler shift. Then we should feed the same signal through HackRF, record it with jGPSv3, and try feeding *that* to the correlator. If that doesn't work, I don't know what's wrong; bad noise maybe? If it does work, we can also try simulating some Doppler shifts and adding varying amounts of noise in GNU Radio. After that: don't we know some folks who make GPS satellite simulators? We're ready to ask them for help. In parallel, I think it's time to do the other engineering tasks we need: send the COTS GPS data to Ethernet simultaneously with the MAX samples; log it all to disk on the FC; stream the COTS data to the ground; and log it all to SDCard on the STM if we're going to do that. I suspect that's mostly on Theo's plate, but anyone who's interested in the microcontroller firmware or flight computer software could help. > + Jamey said we could fly with this configuration and probably figure > out how to tease satellites out of the logged data later. I won't swear there's anything to tease out. I just think at this point we've mitigated most of the risks of hardware problems. So if we decided to fly with the hardware in this state, I'd feel pretty comfortable that we'd done our due diligence toward getting useful science out of the flight. And I think I should shift to focusing on roll control and overall system engineering details. > + For fun, Kenny collected a larger sample outside from the MAX2769, ... Could you post that larger sample somewhere? How big is it? And out of curiosity, do any of the general purpose compression algorithms (gzip, bzip2, etc) manage to compress it at all? (If they do we've probably screwed something up, so that would be good to know.) Maybe we can try feeding the sample into the GNSS-SDR code we looked at last fall, as another check. I think that's a good task for K if he has time; he had that code running successfully IIRC. Jamey
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