Posted by Brian Hudson on September 27, 2009 at 4:38pm
Tom and I just got our uBlox5 combo, and I hooked it up to my arduino as a Serial passthru using NewSoftSerial, with the built in and software port running at 38400. At first I thought I'd go ahead and port the parsing code from the arduPilot to run on my PC so I could get a good feel for what was going on.First - in the version of arduPilot I downloaded (2.31 I think), I think there may be a bug. The checksum seems to have an odd condition check on line 86:if((ck_a=UBX_ck_a)&&(ck_b=UBX_ck_a)) //Verify the received checksum with the generated checksum..I assume these should be using the comparison operator (==) not the assignment operator (=). As it stands, the if-statement always evaluates true (blowing away ck_a and ck_b in the process), and the checksums aren't actually doing any checking! I may be smoking something here, but it sure seemed that way to me.Next, when I changed that in the code, I noticed I was getting ALL sorts of invalid packets mixed in with valid ones. Upon debugging/investigation (and later, some time spent in the uBlox u-Center program), I found that my chip was spitting out the following:B5 62 1 3 10 0 1E 45 BE 1 3 DD 0 0 30 CC 0 0 D8 4 1 0 EF EE VALID NAV-STATUS messageB5 62 1 2 1C 0 1E 45 BE 1 XX XX XX XX XX XX XX XX F1 3 1 0 B5 4C 1 0 CE 28 0 0 24 2A 0 0 A2 CF VALID NAV-POSLLH message - with my lat/lon masked :)B5 62 1HUH??? This isn't even a full valid message header!B5 62 1 3 10 0 18 46 BE 1 3 DD 0 0 30 CC 0 0 D2 5 1 0 E5 88 VALID NAV-STATUS messageB5 62 1 2 1C 0 18 46 BE 1 XX XX XX XX XX XX XX XX 54 3 1 0 18 4C 1 0 C8 28 0 0 1F 2A 0 0 4F 16 VALID NAV-POSLLH message - with my lat/lon masked :)The pattern repeats like that. Effectively, I'm getting a nice NAV-STATUS and a nice NAV-POSLLH. I know the chip was supposed to be set up to also send NAV-VELNED. But when I look at the message viewer in the ublox software, it just categorizes this short message as UNKNOWN, which is what I would expect.My first assumption was that this was a problem with serial communication, but honestly, I get beautiful data for the other messages, and these short goofy B5 62 1 messages are VERY consistent. I also went ahead and did a raw binary to HEX conversion on the Arduino side and sent that over to a terminal program and verified that I was getting the same data that way.I've tried all sorts of things in the ublox software (changing speed from 38400 to 57600 on the Arduino, uBlox and ublox software, although I haven't tried lowering it). I turned on NMEA messages, and those worked fine, but after turning on a combination of NAV-VELNED and any other messages, this weird UNKNOWN message starts showing up in place of the NAV-VELNED.Has anyone dealt with strange behavior like this? I tried to do a brief web/forum search, but details seem to be pretty scarce in this area.I'm kind of out of ideas at the moment, so I'd appreciate any fresh ones you all may have.Thanks,Brian
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Ever since I switch to uBlox my navigation has stopped working, so I think there is indeed something wrong with the latest code rev. I've pinged Jordi to see if he can find the bug.
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