Hi Vincent, Both my tests (the one that worked and the one that didn't) were on exactly the same piece of hardware, an ESP32 microcontroller with a BMI085 connected to the SPI port. The the driver test code (which worked) was moved into a larger data acquisition program without changes, and that fails. The hardware is using an ESP32 microcontroller. The only difference I can think of is that the larger program has wifi enabled, so their might be some slight timing differences or differences in the activity on the ESP32's two cores. There does not appear to be any problems with the logic analyzer traces other than the small difference I mentioned in my original post. The SPI interface was set at 4mhz, I tried taking it down to 1mhz but there was no change. If there is some way of detecting a download error it would be really handy. In my case what ever is happening is happening every single time when I try to start the BMI085 using my larger program. As I said, the BMI085 driver code and initialization is the same in both the test program and the data acquisition one and, except for the small difference I mentioned earlier, the two logic analyzer traces look identical.
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