Dreamcast gun communication

[Guimli]

Hello,

I'm playing a lot of rail shooter recently and I have some questions about the Dreamcast guns and how they communicate with the console.

What I understand is that there is a special light gun mode in maple protocole, but I haven't find more infos.

Does the guns only send messages as trigger pressed and then when it seems light or not, the games guessing the position aimed with those infos?

Or does the gun itself calculate the position aimed (it would need infos about the image by the Dreamcast...) and then give X and Y infos of the aiming to the console?

If someone some doc about that I would be interested.

[SEGA RPG FAN]

If similar to other guns, X and Y would come from a time measurement of the CRT scanning beam. Press trigger, calc time elapsed until the gun sees the beam, figure out screen position from that.

[Guimli]

Yes that's right, but my question is how the gun communicate with the Dreamcast.

Does the gun simply send the sensor info to the console? If yes I could imagine using a master system phaser on the Dreamcast using megavolt adapter (after some modification)?

[TapamN]

Light gun sensing on the Dreamcast work similarly to how it does on the Master System (light gun reports when it sees light, console uses when to figure out where), but the protocol used is different.

I think the SMS/Gen/Sat all basically have a dedicated pin on the controller port for the light gun signal (the pin might be used for other things on other controllers, but on light guns, it's dedicated). The Dreamcast's controller port is normally more like USB in that the console sends commands over a serial interface to the controller and the device responds, but there's a special light gun mode/command where the console waits for a light gun signal on a specific pin like on older consoles.

The light gun still needs to support the regular serial mode so that it can report what kind of device it is, allow VMU access, report the trigger/d-pad, etc. The light gun mode is only used when the console wants to measure where the light gun is pointed.

[megavolt85]

If yes I could imagine using a master system phaser on the Dreamcast using megavolt adapter (after some modification)?

no, SDCKB exclusive mode not supported.

04_Gun061e.7z

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[Guimli]

Thank you Megavolt, it was really interesting, even if I didn't understand everything.

Do you have an opinion on why the Dreamcast gun can't compete with Namco guncon?

Gun conception (optical or sensor signal filtering) ?
Synchronisation between gun signal and console hv counter?
Aim point calculation algorithme by the game (based on the sensor signal)?

I just bought a Guncon, an the accuracy is really surprising.