[Dumb user] Freesync support ?! :-)

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[Dumb user] Freesync support ?! :-)

Postby mahen » Sat Apr 06, 2019 8:43 am

Hi ! Here's yet another post from a clueless spoilt-user...

Does it make any sense to ask if the low-lag mode (single buffered I guess) could theoretically play along with the FreeSync feature of recent monitors in order to reduce input lag even more ? I made a quick search on the forum and saw no mention of it.

Cheers & thanks to all involved for this great project :-)
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Re: [Dumb user] Freesync support ?! :-)

Postby Newsdee » Sat Apr 06, 2019 9:29 am

It's a moot point. Freesync is about making your monitor go potentially slower than 60fps so it matches your processing speed...

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Re: [Dumb user] Freesync support ?! :-)

Postby mahen » Sat Apr 06, 2019 9:40 am

Ah OK, I thought it was to make it possible to get a tear-free display with VSync off, which means the buffer swap could happen at an arbitrary time. Hmm, OK then, if there is a buffer swap, it's still a double buffering, so freesync + single buffering makes no sense ?

I'm probably mixing stuff...
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Re: [Dumb user] Freesync support ?! :-)

Postby Sorgelig » Sat Apr 06, 2019 10:21 am

What is happening in MiSTer has no relation to Monotor's internal work.
And vice versa.

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Re: [Dumb user] Freesync support ?! :-)

Postby ijor » Sat Apr 06, 2019 12:09 pm

I actually think that it would be nice to implement Freesync support. It might allow to achieve the same thing that Vsync does, and even more, but with a method officially supported by the monitors.

Unfortunately no of those variable/adaptive refresh rate standards is fully disclosed. I could never found a detailed technical description. Freesync is supposed to be a free standard, but specifications, AFAIK, are not publicly available.

And as we talked about this some months ago, even if we could get all the information, it is not clear if it would work with the HDMI chip that the nano currently has. Probably yes, but hard to be sure.
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Re: [Dumb user] Freesync support ?! :-)

Postby Sorgelig » Sat Apr 06, 2019 1:06 pm

Freesync means supporting any refresh rate and pixel clock. So it's basically what MiSTer needs with vsync_adjust=1/2 option.
So, nothing additional is required. It's already there.

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Re: [Dumb user] Freesync support ?! :-)

Postby ijor » Sat Apr 06, 2019 2:32 pm

Sorgelig wrote:Freesync means supporting any refresh rate and pixel clock.


Where you got the info that Freesync is that? AFAIK, it is not .

As I understand it means a variable refresh rate by adjusting the vertical blank. Pixel clock remains at the standard value. And it requires, or it might require, some negotiation with the display. This is at least according to the very little information that is publicly available. I don't have access to the formal official standard, do you?
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Re: [Dumb user] Freesync support ?! :-)

Postby mahen » Sat Apr 06, 2019 3:24 pm

Dunno if it helps but Freesync support was recently added to Linux & open source (AMD/Intel) drivers / MESA...
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Re: [Dumb user] Freesync support ?! :-)

Postby mahen » Sat Apr 06, 2019 3:30 pm

As I understand it means a variable refresh rate by adjusting the vertical blank.


Yep ; but I wonder if it enables to use a single buffer and keep a tear-free display ? (which would lead to a significant input delay decrease)
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Re: [Dumb user] Freesync support ?! :-)

Postby Sorgelig » Sat Apr 06, 2019 6:04 pm

ijor wrote:Where you got the info that Freesync is that? AFAIK, it is not .

As I understand it means a variable refresh rate by adjusting the vertical blank. Pixel clock remains at the standard value. And it requires, or it might require, some negotiation with the display. This is at least according to the very little information that is publicly available.

Unlike analog signal, data in HDMI is synced by clock. Very cheap chinese displays happily accept any pixel clock and even fully sync to non standard refresh rates. The only problem with cheap monitors is rubbish quality of panel. Otherwise they would be a perfect monitors for MiSTer.
I don't see why expensive gaming monitors should not accept any pixel clock as cheap chinese monitors. It's should be their nature.

ijor wrote: I don't have access to the formal official standard, do you?

no, i don't.

mahen wrote:Yep ; but I wonder if it enables to use a single buffer and keep a tear-free display ? (which would lead to a significant input delay decrease)

It only means you are not aware that MiSTer already supports single buffer tear-free output.

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Re: [Dumb user] Freesync support ?! :-)

Postby Noggin » Sat Apr 06, 2019 10:25 pm

I'm using a HP Envy 27s 4k-display with FreeSync support and while this monitor is really smooth when paired with an XBOX One X, for some reason MiSTer looks very jittery on it when not using 60fps synced to the display.

Pinball Fantasies' attract mode (with the table scrolling vertically and the display on top horizontally) running on a PAL Minimig looks really, really bad in all vsync-settings whereas it is perfectly smooth via VGA (as it should be).

Can someone confirm that this can look perfectly smooth via HDMI?

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Re: [Dumb user] Freesync support ?! :-)

Postby ijor » Sun Apr 07, 2019 2:50 am

Sorgelig wrote:Unlike analog signal, data in HDMI is synced by clock. Very cheap chinese displays happily accept any pixel clock and even fully sync to non standard refresh rates. The only problem with cheap monitors is rubbish quality of panel. Otherwise they would be a perfect monitors for MiSTer.
I don't see why expensive gaming monitors should not accept any pixel clock as cheap chinese monitors. It's should be their nature.


I agree that it would be good if they would accept non standard pixel clocks, but fact is that not all do. And those that do accept an arbitrary pixel clock, don't support this officially. Regardless, that is not Freesync.

The advantage of Freesync, besides being a formal standard, is that it probably makes easier to solve the problem of matching the input and output refresh rates. Because Freesync is a variable refresh rate, you can compensate changing the number of cycles on each frame, knowing that the monitor (as long as it support Freesync) will accept that gracefully.

Hopefully Freesync would eventually become an universal standard supported by all monitors.

mahen wrote:Dunno if it helps but Freesync support was recently added to Linux & open source (AMD/Intel) drivers / MESA...


Not sure that would help too much. PC drivers don't talk directly to the monitor as we do. A PC driver interacts with the GPU and the graphic card and then it doesn't need all the low level details about Freesync.

Yep ; but I wonder if it enables to use a single buffer and keep a tear-free display ?


I think it should be possible. But at Sorgelig pointed out, MiSTer can already do that, at least on most cases, without Freesync.
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Re: [Dumb user] Freesync support ?! :-)

Postby Sorgelig » Sun Apr 07, 2019 6:52 am

Instead of changing the pixel clock it's possible to change the size of VBlank. I think variable VBlank won't work with HDMI audio. I didn't test this kind of video. Not sure how many monitors support it.

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Re: [Dumb user] Freesync support ?! :-)

Postby mahen » Sun Apr 07, 2019 9:50 am

I think it should be possible. But at Sorgelig pointed out, MiSTer can already do that, at least on most cases, without Freesync.


Hmm, so it's possible to get a tear-free picture in single buffering on a standard screen ?
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Re: [Dumb user] Freesync support ?! :-)

Postby ijor » Sun Apr 07, 2019 12:06 pm

Sorgelig wrote:Instead of changing the pixel clock it's possible to change the size of VBlank. I think variable VBlank won't work with HDMI audio. I didn't test this kind of video. Not sure how many monitors support it.


That seems to be precisely how Freesync works, changing Vertical Blank duration, even on a frame by frame basis. I suspect this won't work on non Freesync monitors. I'm not even sure it will work on Freesync monitors just like that. It seems that you first must tell the display to enter Freesync mode.
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Re: [Dumb user] Freesync support ?! :-)

Postby mahen » Sun Apr 07, 2019 12:40 pm

[BTW, Freesync is getting kinda standard now, even Nvidia is beginning to support it (in addition or instead of ? G-Sync) ; and it's present on tons of new cheap monitors.]
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Re: [Dumb user] Freesync support ?! :-)

Postby ijor » Mon Apr 08, 2019 1:09 am

mahen wrote:[BTW, Freesync is getting kinda standard now, even Nvidia is beginning to support it (in addition or instead of ? G-Sync) ; and it's present on tons of new cheap monitors.]


Yes, Freesync is starting to become more mainstream. But note that Nvidia's support is very partial and limited so far. Among other things, it doesn't work over HDMI (as AMD's Freesync does), only over DisplayPort. Furthermore, I just learnt that the DisplayPort must be directly connected to the GPU. Using, a ThunderBolt to DispalyPort adapter usually doesn't work :(
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Re: [Dumb user] Freesync support ?! :-)

Postby Sorgelig » Mon Apr 08, 2019 1:59 am

I think this Freesync is more about sync to game frame rate through the whole chain. For example, PC is not power enough to handle the game at 60FPS, so it can produce variable frame rate let say 55-60FPS. So, this freesync allows to keep the game picture till next will be ready. So this feature avoids refresh between pictures which will give smooth move although actual frame rate may vary from frame to frame.
Most likely this feature work toward lower frame rate only. FPGA cores may produce slightly faster FPS than standard.

I'm not sure if it will be easy to adapt such feature. And of course technical documentation is required. Probably it's simple VSync delay, but still docs are needed.

While such monitors may become more popular, it's still not a mainstream.

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Re: [Dumb user] Freesync support ?! :-)

Postby Dubon » Mon Apr 08, 2019 8:44 pm

It all depends on the monitor. My monitors freesync range is from 40 to 144 hz. Others may vary but ive never heard of one that tops of at 60hz. 75hz is probably the freesync max on the cheapest displays.

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Re: [Dumb user] Freesync support ?! :-)

Postby jemismyname » Mon Apr 08, 2019 9:55 pm

Sorgelig wrote:
Unlike analog signal, data in HDMI is synced by clock. Very cheap chinese displays happily accept any pixel clock and even fully sync to non standard refresh rates. The only problem with cheap monitors is rubbish quality of panel. Otherwise they would be a perfect monitors for MiSTer.
I don't see why expensive gaming monitors should not accept any pixel clock as cheap chinese monitors. It's should be their nature.


I agree with this, I actually have a great little chinese monitor that i got off of wish.com to play with my MISTer in my car. it is only 480 p (so it doesn't work right with all the scanline options), but it is fast refresh (5ms) and very responsive. It is also very supportive of many different inputs (composite, vga, hdmi, bnc), and it is very bright with good color... Chinese displays and projectors are the best for supporting a multitude of input options!

https://www.wish.com/product/5b7423d6199cdb1412ee4b3c

and no, i don't play video games while driving...

(officially)

is that illegal?

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Re: [Dumb user] Freesync support ?! :-)

Postby mahen » Tue Apr 09, 2019 9:25 pm

Is there somewhere a list of monitors properly supporting the tear-free low lag mode (vsync_adjust=2) ?

If not, may I create a thread to ask users about it ?
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Re: [Dumb user] Freesync support ?! :-)

Postby Sorgelig » Wed Apr 10, 2019 4:55 am


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Re: [Dumb user] Freesync support ?! :-)

Postby mahen » Wed Apr 10, 2019 7:41 am

Ah, thank you Sorgelig, this is gonna be interesting !
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