How to track VDU-Driver activities

I want to track the activities of the VDU driver. Which vectors must be claimed to do so?

SpriteV could be a candicate. VDUXV is useless for I don’t want to rewrite anything or is it possible to take the call and to bypass it to the regular VDU handler? OS_Plot I assume can’t be tracked so programs could bypass the tracking.

Any ideas?

Many thanks in advance!

Which vectors must be claimed to do so?

Is this possible?

I mean, writing text (PRINT “Hiya!”) is likely to call WRCHV but nothing else even though the screen is updated. You can’t trap that part of the activity.
What about OS_Plot? IIRC, UKPLOTV is only called if the plot code is unknown. I guess standard plotting doesn’t notify anything.
VDUXV only works if the VDU output is redirected.
Don’t forget ColourV and PaletteV and these days, maybe GraphicsV too.

I don’t want to rewrite anything or is it possible to take the call and to bypass it to the regular VDU handler?

To pass on the call, return to the address provided in R14, the usual MOV PC,R14.
To intercept the call, pull the return address off the stack, like LDR PC, [R13], #4 (which is a nicer way to say LDMFD R13!,{PC}).