BNO085 I2C VS SPI issue

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getEmbedded
 
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BNO085 I2C VS SPI issue

Post by getEmbedded »

Hello everyone!

I am currently looking to acquire data (linear acceleration, gyroscope and rotation vector) from 2 BNO085s as quickly as possible. I am interfacing with a BeagleBone black. I started using I2C because it seemed the easiest.
The maximum frequency I was able to achieve was about 55 Hz (with the 2 BNOs) which is not bad but a bit far from what I expected knowing that it could go up to 400 Hz according to the datasheet (But I saw other posts complaining about the frequency drop when using multiple reports, so I wasn't surprised).

Then I decided to try it with SPI. Looking at the signals on the oscillo, the communication time was much faster (just to receive a packet from BNO) which shows good potential. But a problem with packets and reports appeared when using SPI.

When I requested one report per second from BNO for all three types of reports, I had no problem, the packet arrived every second with all three reports. But when I set the report delay to 5ms less or more, I got a packet about right in timing that contained only one report.
In the end, I couldn't get the report delay below 20ms AND a packet containing all three reports... Have you heard of this problem (I haven't seen anything on the internet)? Is it a software problem with the BNO? Have I reached the performance limit of the BNO?

Thanks in advance!

PS: I don't use the interrupt pin for practical reasons. So I ask the BeagleBone to read the BNO values periodically. I tune this period and the reports delay so that I always have something to read. This worked well with I2C...

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gammaburst
 
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Re: BNO085 I2C VS SPI issue

Post by gammaburst »

I while ago I experimented with talking fast to three BNO085s over I2C and SPI. Difficult journey. Problems with other people's code, especially the BNO's awful communication firmware. My test results were disappointing, although a lot faster than 55 Hz. I forget the details. Maybe something in the discussion will help you:
Three BNO085s I2C: viewtopic.php?p=857930#p857930
Three BNO085s SPI: viewtopic.php?p=859651#p859651

Adafruit's forum just now tried to ban my word "disappointing".

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getEmbedded
 
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Re: BNO085 I2C VS SPI issue

Post by getEmbedded »

Thanks for the quick answer gammaburst !

I checked the past discussion and for the moment I could already understand another bug I had. Sometimes not all the reports were enabled at the begining of the code (in SPI, not I2C) and I didn't see why. I understand that I didn't get the complexity of the BNO firmware...

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