Chaining 16 bit timers to a 32 bit timer. Am I understanding it?

Might as well learn something as long as the cubemx app isnt getting it right

I get stumped by the terminology sometimes because it tends to vary in the documentation.

In order to chain together two 16-bit timers into one 32 bit timer, I need to:

set up the first timer as oc output one pulse mode

do I want the slave in reset mode or gated mode?