ULP I2C demo application

Example of ESP-32 ULP I2C application which reads a sensor (BMP-180) and wakes up the main processors after a significant change of the measured values.

Note that the ULP is quite limited in program size and IO options. An alternative is to use an ATTiny as ULP processor, see:

https://github.com/tomtor/ESPTiny

IDF requirements

Tested on IDF 4.1 with CMake build system

I2C bit banged support

Note that this example uses a bit-banged I2C implementation, because the hardware ULP I2C support cannot read 16 bit values. This is not essential for the BMP-180, but some sensors like the ADS-1015 DO require 16-bit readouts.

Example of Macro usage and ULP stack/subroutines

In additon this example shows ULP stack handling and reusable subroutines examples, like

waitMs

Wait some milliseconds

abs

Compute abs value of register

Credits

Parts of the original C code from

https://github.com/adafruit/Adafruit-BMP085-Library

were translated to ESP assembly.

Warning

Be aware of an assembler bug:

https://www.esp32.com/viewtopic.php?f=2&t=3228