I am trying to sample an I2C IMU with 8Khz with an ESP32. I read just the Acceleration X,Y,Z axis
The I2C bus runs with 1Mega.
Generally it works for sampling.
But I can only use 2kHz. I looked at a sample and there is a long "Break" from 113uSec.
Can I make this break shorter somehow?
One IMU, One Sample:
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Program part:
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2025-02-03_14-31-40.PNG (45.22 KiB) Viewed 4657 times
How are you reading the sensor ? Can you post the code - the delay must be due to 'something' happening that is taking 112uS - so a print to UART / write to SD or somesuch - the reads should be continuous unless the task doing the read 'yields' (a delay - or call that does so (UART Prints do I think))) or is doing 113uS worth of work between reads?
I'm assuming ReadNRegisters - reads all registers correctly using in the 'bursts' on the trace - and the delay is between calls to this?
The i2c should run okay - unless the sensor is using clock-stretching to delay things (is it capable of being read at 2kHz or does it do some data processing ?)
Good idea Martin.
Instead of switching everything off, I made a new program
Now I have tested the senor in a small test program without Sd-card and uart and no IRQ.
It is the same.
123uSec
Then I tested other components and there is also a waiting time. This is different depending on the component, but between 69uSec to 123uSec
That's bizarre. It looks like the transaction write to set the register address followed by the a pause before the transaction read?
But would expect the same if using software i2c and you are not seeing that.
Do you see the same at 100/400kHz or is it just with 1MHz i2c? The mcu should be able to easily do 1MHz - I'll try and test on an i2c chip but don't imagine it will struggle..
The gyro sensor read n regs (component) doesn't do anything odd does it?
I tried it directly with the code abstract layer.
I can display the values with the UART.
But with the oscilloscope I measure the same duration
Total 174uSec with a break of 73uSec
What I still don't understand is the command “Write start address” with this parameter 0x8001
Program:
2025-02-04_14-32-47.PNG (165.05 KiB) Viewed 4518 times
I've just tested using a i2c eeprom - and set for a similar scenario. So doing the same (effectively) as GetNRegs - using hardware i2c there is a delay of ~75uS before the read. This doesn't happen with software mode.
Setting the high bit (0x800n) of the number of bytes to send doesn't send a 'stop' on the i2c - then the read can follow.
This gives a total time to read 10bytes (I went one better )of 2.46ms in software mode. and 256uS in hardware mode - so it's probably worth using hardware mode anyways? Still odd though - might be the sensor is holding SDA low for some processing?
