Hello Jens,
I need taking some time to look into your code but, the first of all, may you tell you what is the problem or issue?
You mentioned that the TSC2004 interrupt output pin (PINTDAV) starts to taggle as soon as the I2C starts communicating to the TSC, which is correct or as expected if the host processor asks for touch data through I2C commands. Refer to Figure 30 at pg 20 of the TSC2004 d/s --- the /PINTDAV pin (if programmed as Pen Touch) is disabled internally and becomes low whenever the X+ or Y+ driver is ON.
Regards,
Wendy F.