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Vertical Refresh Rate: set by game software or monitor hardware?
torino:
Game: Galaga
Resolution: 224x288
Frequency: 60.606061Hz
VSync, the thing we need for smooth scrolling and steady animation. As far as I know it is the game software that waits for monitor hardware to say when is the time to update video buffer, not the other way around. So how did they get those numbers? In some manual, maybe specification sheet, or did they actually measure it with some instruments? But what would they measure, monitor properties or some PCB output signal? Is vertical refresh rate then a property of a given monitor, or of the game?
What happens when we plug Galaga PCB to arcade monitor with fixed 60Hz?
Thank you.
ahofle:
The PCB will drive the appropriate resolution/refresh of the arcade monitor -- it doesn't wait for any feedback from the monitor. Also, there is no 'fixed' 60hz on a true CRT monitor, but rather a range of values that define the supported frequency/range of the monitor.
torino:
--- Quote from: ahofle on March 27, 2011, 04:53:07 pm ---The PCB will drive the appropriate resolution/refresh of the arcade monitor -- it doesn't wait for any feedback from the monitor. Also, there is no 'fixed' 60hz on a true CRT monitor, but rather a range of values that define the supported frequency/range of the monitor.
--- End quote ---
How exactly do you propose PCB can "drive" monitor refresh rate? Do you think vertical refresh can vary from frame to frame, so when the game software slows down it would accordingly slow down monitor refresh rate? Of course not, and of course the software (good one) waits for VSync signal, otherwise we get choppiness and tearing.
Yes, CRTs seem to be flexible, even TVs can take quite a range, but what about old CGA PC/Amiga monitors, they had 15kHz horizontal and fixed 60Hz vertical refresh, I think. Or how about LCD arcade monitors, what's their refresh rate and what would happen if we plug Galaga PCB to such monitor? In any case the question remains - how did they obtain that number?
ahofle:
--- Quote from: torino on March 27, 2011, 05:52:16 pm ---
--- Quote from: ahofle on March 27, 2011, 04:53:07 pm ---The PCB will drive the appropriate resolution/refresh of the arcade monitor -- it doesn't wait for any feedback from the monitor. Also, there is no 'fixed' 60hz on a true CRT monitor, but rather a range of values that define the supported frequency/range of the monitor.
--- End quote ---
How exactly do you propose PCB can "drive" monitor refresh rate? Do you think vertical refresh can vary from frame to frame, so when the game software slows down it would accordingly slow down monitor refresh rate? Of course not, and of course the software (good one) waits for VSync signal, otherwise we get choppiness and tearing.
--- End quote ---
It "drives" it the same way Windows "drives" it when you select a particular resolution. That's what the sync wire(s) in a VGA cable are for. I didn't say anything about varying the sync from frame to frame, not sure where you pulled that from. Wait for vsync just means that the application will match its internal frame rate to the exact sync of the monitor, which is a known value by the application or PCB. The game is not "listening" for anything from the monitor. You are suggesting that the application or game will stop running if you disconnect the monitor because it then can't get the vsync "signal". ???
I don't know how the vertical refresh rate for Galaga was determined, but it is just one variable in a fairly complex function. Read up on modelines for more information.
SavannahLion:
ahofle, I may be wrong here, but it sounds like the OP is attempting to apply modern architecture concepts to the old hardware. I mean... feedback from the monitor?
To the OP.
Arcade monitors, heck, most any monitor from that era don't have any "feedback" on the state of the monitor. Either the signal gets there or it doesn't. If it doesn't, it's called playing blind. The frequency rate is something that is/was established by the industry as a whole. There is a ton of history behind the design of the CRT and the how and why countries like the U.S. chose 60Hz whereas other countries use 50Hz. Why computers up to a specific speed never used a video card (hint: check the history on the South Bridge). Why buffers aren't used on some boards. So on and so forth.
The short answer is the developers already know the frequency rate of the monitor going into the design of any game. Remember, CRT (and later LED/LCD/Plasma/whatever) manufacturers don't cater to just arcade cabinets. Those tubes and panels are manufactured for a wide range of applications.