Quote:
Originally Posted by slibert
No word on a resolution by NI - it's likely been because we can't give them a reproducible case; Joe Hershberger of NI has indicated suspicion of a lock not being held correctly during opening of the MXP port, but that hasn't been confirmed.
However in testing it's been discovered that the various communication peripherals on the navX MXP are experiencing bus errors sometimes when the RoboRio is starting up (e.g., upon initial power up, and when "Reboot RobRIO" is selected in the driver station, but not when restarting the robot code). In these cases, a few seconds after the reboot occurs (about one in every ten times) I2C circuits on the navX (including - notably - the internal I2C bus which communicates with the MPU-9250) experience bus errors. My suspicion is that problems occur when the robot app opens a MXP port before the RoboRIO FPGA code that manages the MXP port has completed initialization, and the result is the navX MXP experiences random noise during that time. And the fact that an internal (non-MXP) I2C bus is experiencing error implies the noise is on the power/ground which are used to pull up the internal I2C bus lines. I haven't got it captured on a scope yet, but my hunch is there's a noisy MXP ground sometimes during RoboRIO startup.
[These errors can cause navX MXP comm to the MPU-9250 to lockup. The visible symptom of the internal I2C bus lockup is that only one of the two Green LEDs on the navX MXP will be lit up (in normal operation, both LEDs should be on).]
So the reasonable conclusion is that when using MXP-based SPI/I2C, the navX was being exposed to more of these glitches than when using non-MXP communication, and every now and then could no longer talk to the MPU-9250.
The recent navX MXP firmware has added code to detect these bus errors and reset the affected communication peripherals. In testing, we were able to reproduce the error, and demonstrate successful recovery by the navX MXP firmware. Based on that, I believe the latest navX MXP firmware is resilient to these transients. However these transients could impact other MXP devices too, so the plan is to document this and send the findings to NI and to the ChiefDelphi community.
I'll send out a general update to ChiefDelphi once the latest navX MXP firmware has passed all our tests and is ready for release; I'd recommend retesting at that time, believing the above was the root cause for the sporadic startup failures you saw.
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It's interesting that you have problems with the MXP. We experienced exactly the opposite. Our Lidar would simply not function on the dedicated I2C port on the roborio, but worked perfectly on the MXP port with the exact same code.
Anyway, this thread has been outstanding so far. I've always had trouble finding inexpensive sensors that work well for our system and have relied on what I've seen on other robots. For instance, one of our favorites was always the sick ZL1 series that we ordered from automationpartsexpress.com for under $40 (credit to 33 and Jim for finding them), but they seem to be out of business.
It'd be fantastic if people kept suggesting sensors they use. So far, I have this list:
Sensor Type Part # Website
Encoder, multiple shaft, multiple counts per rev AMT10-V
http://www.cui.com/product/component...ar/amt10-v-kit
Magnetic reed switch / position switch 59140-010-ND
http://www.digikey.com/product-detai...0-010-ND/43977
IR reflective 42EF Rightsight
http://ab.rockwellautomation.com/Sen...tSight-Sensors
IR Reflective / cheap 30 CM E18-B03P1
http://www.amazon.com/6-36V-Photoele...lectric+sensor
Hall effect switch / position switch WCP-0971
http://www.wcproducts.net/sensors
Hall effect switch / position switch MC1104
http://www.amazon.com/Effect-Sensor-...y+Switc h+NPN
SICK photoelectric Z series IR sensors ZL1-E2415 Not available
So we've got IR reflective and hall effect reed/limit switches. What about cheap through beams (that aren't garage door sensors)? One of the nice features on the Allen Bradley RightSight was the manual adjustability so that it would work with reflectors, or even colored tape. It was also capable of 10000+ samples / second. What else is out there with those capabilities?