greyltc / arduino-wire.h

non-blocking Wire.h for Arduino

Arduino-Wire.h

Wire.h with timeout for Arduino.

Tests:

Tested using generic DS3231 module with 32kbit EEPROM.

Case	SDA	SCL	Power	Situation
1	disconnected	disconnected	connected	as if no device
2	disconnected	connected	connected	address NACK detected
3	connected	disconnected	connected	address NACK detected
4	connected	connected	connected	ideal case
5	disconnected	disconnected	disconnected	as if no device
6	disconnected	connected	disconnected	BLOCKS/HANGS
7	connected	disconnected	disconnected	BLOCKS/HANGS
8	connected	connected	disconnected	BLOCKS/HANGS

If the SDA/SCL lines are accidentally disconnected the original Wire.h is able to detect the error. However if the power is cut, it blocks on the call to Wire.endTransmission().

This version will instead return an error after a specified timeout.

To use just replace the #include directive to point to it. Then set the timeout using:

  Wire.setTimeout( milliseconds );

Without setting the timeout it behaves exactly like the original version.

Changes:

All while loops were changed to monitor timeout.

Function	Changes
twi_readFrom()	returns 0 bytes read on timeout
twi_writeTo()	returns 4 on timeout, which is described as "other twi error" in the original library
twi_stop()	made to return a bool. returns false on timeout