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Is there some calculator to find the porches for a given scanrate/refresh range?

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Gray_Area:
Mine are 15-48khz; 55-65hz.

Calamity:

--- Quote from: Gray_Area on March 11, 2012, 03:29:31 pm ---1. Why does one have to put in the porches and all that/why isn't the pixel clock (range) enough like it was in AdvanceMAME?

--- End quote ---

You don't need to put in any porches actually, you can just go with any of the monitor presets. Think of porches as the size of the picture's borders. By finding the correct values for your specific CRT, you make sure all the modes will get automatically centered.

AdvanceMAME didn't need this because it just worked based on predefined reference modelines. The porch values where "extracted" from these modelines to produce new ones, by interpolation. This usually resulted in nearly correct modelines, but that's not guaranteed when using this method.

The method used by VMMaker/GroovyMAME ensures that each element of the resulting modeline has the correct size, by checking these values individually.


--- Quote ---2. How does one find out what the porches should be? Is there some calculator you can put in the scanrate and refresh and it'll spit them out??  (Mine are 15-48khz; 55-65hz)

--- End quote ---

The easiest way is to use Arcade_OSD to find the values interactively. One would start by displaying some standard arcade modeline, which will be more or less off depending on the case. Then, entering the geometry menus in Arcade_OSD and tweaking the modes until you get a perfect fit. Then, all the needed porch/sync values corresponding to this adjustment will be presented in a column on the right. Finally, you write this values down and use them as feedback to build the monitor_specs line that will tell GroovyMAME how to create modelines that are similar to the one you just adjusted.

For your particular case (15-48kHz), you'll probably need to divide that range in several intervals where different porch/sync values apply. What kind of monitor is that?

Gray_Area:

--- Quote from: Calamity on March 11, 2012, 04:24:12 pm ---
--- Quote from: Gray_Area on March 11, 2012, 03:29:31 pm ---1. Why does one have to put in the porches and all that/why isn't the pixel clock (range) enough like it was in AdvanceMAME?

--- End quote ---

You don't need to put in any porches actually, you can just go with any of the monitor presets. Think of porches as the size of the picture's borders. By finding the correct values for your specific CRT, you make sure all the modes will get automatically centered.

AdvanceMAME didn't need this because it just worked based on predefined reference modelines. The porch values where "extracted" from these modelines to produce new ones, by interpolation. This usually resulted in nearly correct modelines, but that's not guaranteed when using this method.

The method used by VMMaker/GroovyMAME ensures that each element of the resulting modeline has the correct size, by checking these values individually.


--- Quote ---2. How does one find out what the porches should be? Is there some calculator you can put in the scanrate and refresh and it'll spit them out??  (Mine are 15-48khz; 55-65hz)

--- End quote ---

The easiest way is to use Arcade_OSD to find the values interactively. One would start by displaying some standard arcade modeline, which will be more or less off depending on the case. Then, entering the geometry menus in Arcade_OSD and tweaking the modes until you get a perfect fit. Then, all the needed porch/sync values corresponding to this adjustment will be presented in a column on the right. Finally, you write this values down and use them as feedback to build the monitor_specs line that will tell GroovyMAME how to create modelines that are similar to the one you just adjusted.

For your particular case (15-48kHz), you'll probably need to divide that range in several intervals where different porch/sync values apply. What kind of monitor is that?


--- End quote ---

This is similar to the manual method (xclock) to AdvanceMAME. I tried the manual method, but found the auto to work just as, well without the work. I was hoping GroovyMAME had gotten to this point. Hmmmmm.......

Calamity:
Well, I admit that having some sort of 'auto' option would be an interesting add-on.

It's just that in the arcade world there's no standard specification you can trust. They used to have the same problem in the PC industry, that's why they created the VESA standard, where porch values and sync pulses are calculated out of some well defined formulas. There's nothing like that for arcade monitors.

Anyway it would be possible to gather a bunch of safe enough values for different frequencies, in order to build an 'auto' option as you suggest, that in the worst case at least produces a viable picture, provided the frequency is supported by the monitor.

This 'auto' option would work better or worse depending on how picky one monitor is. Probably some professional CRTs like the NEC Multisync may admit almost anything they're fed with, others definitely will need a big amount of manual tweaking if fed with 'standard' values (the reason behind custom monitor_specs is to eliminate the need for manual tweaking between modes in arcade monitors).

Gray_Area:
I no longer have a page of info on this monitor, though I don't think it had porch data. The NEC XM preset might work, except that monitor goes up to 64khz.

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