This is just a general FYI. It required a couple of days of troubleshooting; so this may save some time for another user.
I have an ESP32 connected to a MCP23017 expander, as I need another 16 I/O points. This is controlled via the I2C buss (GPIO22 and GPIO21).
Running under both Visual Micro and the Arduino IDE.
Reading or writing to a single port or register on the 23017 works correctly in any task (including loop() )
Reading both A and B registers (16 bits) works correctly on any task if you use the following:
portA = Wire.read();
portB = Wire.read();
This requires ~ 125µsec at 1MHz clock.
Setting - Wire.endTransmission (false); // keep the I2C bus open
results in a 70µsec transmission, but the data returned is all 0. You can see on a logic analyzer that the data is never returned on the buss. I can share screenshots if desired.
However, running this command in loop() works perfectly. It fails in any other defined task.
I will use the working model to finish my project, but I would like to understand the issue if possible.