https://retropie.org.uk/docs/Dreamcast/
Redream is best.
\\piboydmg\configs\dreamcast\redream\redream.cfg
profile0=name:15001176010000000100000000010000,type:controller,deadzone:12,crosshair:1,a:joy0,b:joy1,x:joy3,y:joy4,start:joy9,dpad_up:joy11,dpad_down:joy12,dpad_left:joy13,dpad_right:joy14,ljoy_up:-axis1,ljoy_down:+axis1,ljoy_left:-axis0,ljoy_right:+axis0,ltrig:joy7,rtrig:joy6,turbo:f6,menu:joy8,menu:escape,lcd:f5,screenshot:f12
profile0=name:15001176010000000100000000010000,type:controller,deadzone:12,crosshair:1,a:joy0,b:joy1,x:joy3,y:joy4,start:joy9,dpad_up:joy12,dpad_down:joy11,dpad_left:joy13,dpad_right:joy14,ljoy_up:-axis1,ljoy_down:+axis1,ljoy_left:-axis0,ljoy_right:+axis0,ltrig:joy7,rtrig:joy6,turbo:f6,menu:joy8,menu:escape,lcd:f5,screenshot:f12Â
I think hotkey combo might be paid feature. I can't find any examples of someone using it.