How to data-link two Amigas for "RVF Honda" two-player mode

Connecting two Amigas with a RVF Honda "Data Link" cable to play it in two-player mode should be straightforward - but somehow it isn't. 

To try to link two Amigas for RVF Honda, you need a proprietary so-called "Data Link" cable, which you'll probably have to build yourself. Click here for more information.

The game's manual says this about the connection:

DATA LINK (SOME VERSIONS ONLY)

If Datalink is implemented on your version of RVF it will appear as the last item on the main menu. Datalink allows two people to race against each other on the same track using two similar computers, connected by a special cable.

HOW TO USE DATALINK

Both computers should be turned off and then joined using the datalink cable. Load RVF into one computer making sure the other is still switched off. Once RVF has loaded, for Datalink purposes this computer will be the master computer, the only one able to make selections from within the Datalink menu. Now turn on the and boot the other computer using the RVF disk, this computer will now be the slave unit, not capable of making selections from within the Datalink menu. Now select Datalink from the main menu on both computers, the master unit will now enable you to select which track you will race on. Pressing the Escape key during a race will exit Datalink Mode.

This sounds clear and easy, but it turns out not every setup works as expected.

From real-life experience, trying to establish the link, here are some notes that might help if you don't succeed on first try:

- "Once RVF has loaded" means "the game has fully loaded", as opposed to just the intro graphics screen with the music. The game has fully loaded when you see the credits screen:

RVF Honda credits screen indicates game is fully loaded

- You need only one floppy disk. When the game has fully loaded, you can put it into the other (slave) Amiga.

- A (warm) reboot/reset of the slave Amiga won't do, it has to be switched on. 

- Successful connections were made using Amiga 500, 600, and 1200 (no other models tested), and a RVF Honda floppy disk.

- No success was achieved with a WHDLoad version of RVF Honda on Amiga 1200, regardless of master or slave, or other Amiga model. (With, or without, Workbench loaded.)

- Amiga 1200 seems to be particularly picky about the connection, the success rate was low. Also it seems an Amiga 1200 (and probably 4000) can't be used as RVF Honda slaves, because when trying to run the game from floppy disk, "Disable CPU Caches" needs to be selected in "Early Startup Menu" for the game to load, altering the power-up init sequence.

- All CPUs and Kickstart versions seem to be allowed.

Overall, establishing the link just appears to be somehow unreliable. Even a tested, unchanged setup sometimes fails to connect. It's still unclear what precisely is happening, and why it's unpredictable - probably only reverse-engineering of the game's machine code will fully explain how to perfectly "data link" two Amigas.

Do you have experience with RVF Honda's "Data Link" connection?
Please leave a comment - corrections, additions are highly appreciated!