How reliable is the refresh rate reported by MAME?

[BazookaBen]

When you first load a ROM in MAME, you will get a screen that shows a bunch of info about the game including resolution and refresh rate. So is it reading that refresh rate directly from the ROM, or some external database file?

I'm asking because although I'm seeing on a couple websites that Battle Garegga has a vertical refresh of exactly 60hz, the launch screen for MAME reports it as 59.637405. I can create either resolution for Windows via CRU, I'm just not sure which one is correct.

[Ed Oscuro]

At face value, it looks as if MAME's value is more definite than the 60Hz value, unless there's unknown revisions out there. On the other hand, they could be reporting the Saturn version's rate. The refresh rate can be timed with a data logger / oscilloscope - if somebody's just reading "60Hz" off the front of their PVM that's obviously not a worthwhile measurement. Occasionally MAME does change the specified refresh rate or the speed of a CPU.

With CPUs you sometimes can figure out clock speeds by multiplying the stated values of crystals (of course, crystals can drift over time, though I think that mainly affects older equipment, not something as recent as Battle Garegga). The MAME reported value kinda looks like it was derived that way. I'm not sure video output rates are often reliant on a timing crystal in boards, let alone newer ones, though it seems possible.

[BazookaBen]

You could also run the PCB through an Extron RGB with a display and it will tell you to one decimal place. So if anybody has the PCB and feels like investigating let us know.

But yeah, MAME's reading seems awfully specific, so I think I'll go with that for now.

[system11]

Code: Select all

MCFG_SCREEN_RAW_PARAMS(XTAL_27MHz/4,432,0,320,262,0,240)
//MCFG_SCREEN_REFRESH_RATE(60)
//MCFG_SCREEN_SIZE(432, 262)
//MCFG_SCREEN_VISIBLE_AREA(0, 319, 0, 239)

That's why it changed - the refresh rate is now calculated.

Above example from the driver for Battle Garegga.

[BazookaBen]

Sorry, I'm not following your post.

What is changed? And the refresh rate is calculated from what? Just analyzing the ROM? Is this 59.637405hz figure from the loading screen just misreported?

[system11]

It's calculated from resolution and chip specs. Most of the old rates were assumed, few measured.