The DS Input Interface can replay button inputs frame-by-frame in TAS Mode. It also can detect when the battery is inserted to turn on the console, as well as automatically restart the console with precise timing in order to be able to manipulate RNG.
Enabling TAS Mode - Hardware
You'll need to solder two additional wires during hardware installation, to enable power button control and sync to the DS (Instructions on how to do so are provided). When TAS Mode is enabled, the DS will still function as a normal DS (with an Input Interface) with the only quirk being that you must have the Input Interface powered to turn on the DS (Though once the DS is on, you can unplug the Input Interface). The program loaded on the Pro Micro board works for all modes.
The included software can parse DSM files, and adds a few custom commands to make it easier to console-verify TASes and write ones for console without features like frame-advance. You can read more about the DSM parser in the parser program docs here:
RNG Manipulation (RNG Manip)
You'll need to enable the power functions in the DSM file (outlined in the above link). These functions enable the Input Interface automatically turning on and starting a TAS when the battery is inserted, and automatically restarting the DS after user info and date/time is entered. There's a few steps to starting a TAS to ensure that the DS has been completely reset:
TAS Mode Software Setup Recommendations
After all hardware installation is done, I recommend setting up the software for the Input Interface modes 1/2/3 (See Software Installation Instructions Page)