I'm using a gameduino 2 for a simple user interface. I have the touch interface correctly calibrated and touch coordinates read out correctly, but the tag always reads as zero. The default tag is 255, so even without drawing anything, this is what should be read out.
The example Blobs.ino uses only the coordinates and works fine. The example Widgets.ino uses only touch tags and does not work at all, not even the trackers.
I've examined the FT810 datasheet extensively and I can find nothing to indicate why this is not working. I've tried reading from REG_TOUCH_TAG, but this is also always zero. I've checked REG_TOUCH_CONFIG which also appears to be correct, although if it were not I would not expect to get touch coordinates.
I've discovered it's not actually calibrated properly. The screen y coordinate is 1024 higher than it should be. Drawing to this coordinate wraps around back to where it's supposed to be, hence it looked correct. I've adjusted TOUCH_TRANSFORM_F in eeprom to reflect this, but I'm still getting zero from REG_TAG and REG_TOUCH_TAG.