I2C multimaster

I'm start with a project with the Marklin 6021 controler
(for my railway hobby) on this controler on the left and right side are connectors
for the I2Cbus to add another devises.
Marklin 6021 have a multimaster I2Cbus, so all devises add to the controller ara master and slave.
A so called devise is a keybord with 16 buttons when you press a
button it write to the controler that solenoit #3 will switch, the
controller write back to the keyboard when it is possible and the keyboard will be update.

So my questen, i'm looking for some source code for a active
slave with ON INTERRUPT GOTO xxxx

Yoep