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A concerning find - MTen3 firmware reads data from the gyro far faster than its specification


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You're talking about the clock rate of the serial bus, yes?  Great catch.

Yeah, pretty bad idea, but they probably get away with it because the output driver is just clocking out a shift register with ns setup times, and the distance isn't very far.

We used to overclock UARTs all the time back in the day, if errors could be caught.  Basically it'll work until a cat hair changes the capacitance or impedance of that SDA line, then their line sampling will magically not work anymore.  Then, as we used to say, "Hilarity ensues."


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Yeah, the I2C clock rate.

And you are right, it's probably not as bad as it seems for a couple reasons:
1. As you say, most I2C peripherals output data with essentially a shift register, which is very fast
2. This chip only supports I2C, but it has an alternate part number that also supports SPI (over the same pins, just depends on how the chip select pin is configured), and the SPI supports 1MHz. Many chips that support SPI and I2C in this way likely use the same circuitry internally to output the data in both instances

It's possible Invensense just didn't want to go through the effort of officially supporting I2C Fast Mode Plus (1MHz) so just implemented Fast Mode (400Khz). Still, it definitely sketches me out!

And the actual SDA/SCL lines have perfectly fine rise times, I checked with a scope. It's just the data rate that's too high.

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