Pi 3+: fixed pixel clock?

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mbsalles
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Pi 3+: fixed pixel clock?

Post by mbsalles » Wed Mar 31, 2021 9:34 pm

Hi, I bought a RJ for my 15khz cabinet and I'm having a blast. Thank you for this awesome kit!

Most games work pretty perfectly, but I've noticed some issues in games with non-standard refresh rates (i.e. 54hz, 57hz - for example, Shadow Dancer, Mortal Kombat, etc.)

As an example, running Mortal Kombat through the suggested emulator (MAME 0.078 retroarch core), making sure to have "sync to exact refresh rate" enabled in the options (under frame throttle), I'm still not getting 100% smooth scrolling (for example the vertical scrolling character portraits in the title screen after inserting a credit). Shadow Dancer runs great under FBA Retroarch, but scrolling also stutters every once in awhile at regular intervals.

To my mind, this is clearly a refresh rate issue (used to have the same problems running on my 60hz fixed refresh panel) - however, this cabinet has a 15khz CRT so variable refresh should work and lead to smooth scrolling even in these quirky games (other examples I can think of are the Raiden series).

So, I was wondering if this is a limitation with the Raspberry Pi itself? I'm running a Pi3+, does it have a fixed pixel clock? If so, does the Pi4 support variable display clocks?

Thanks in advance!

dee2eR
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Re: Pi 3+: fixed pixel clock?

Post by dee2eR » Wed Mar 31, 2021 11:32 pm

Actually it's an emulator issue. Mortal Kombat isn't run at the correct refresh rate by MAME 078. Not much you can do about it (short of bugfixing the emulator code). The hardware is capable of the correct refresh rate (and in fact uses it) but the emulator runs the game at the wrong refresh due to the emulator not knowing the right one (078 thinks the exact refresh is for MK is something it's not, can't remember the numbers offhand but it's syncing to the wrong speed).

For MK1 you could try using a newer MAME. AdvMAME will run MK1 fullspeed, MAME 0.172 may too, I'm not sure (on Pi3). MK2 & MK3 won't run at full speed in other MAME on Pi3 though as far as I remember.

Not sure re. Shadow Dancer offhand, but it's probably a similar story. If the game is run a the wrong refresh rate by the emulator there's nothing the hardware can do to fix it. Again it may be worth trying AdvMAME, I'm not sure though.

Both the Rpi3 and 4 support arbitrary refresh rates, within reason. They have slightly differing capabilities but mostly can use the same refresh rates. Unfortunately if the emulator is a the wrong refresh speed having the hardware at the right one wont help.

On the plus side Pi4 runs MK1, MK2 and MK3 butter smooth in MAME 0.172, as 172 runs them at the right refresh rate.

mbsalles
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Re: Pi 3+: fixed pixel clock?

Post by mbsalles » Thu Apr 01, 2021 12:24 am

Hey, thanks a lot for the reply. Glad to hear the Pi3 is able to do arbitrary refresh rates and is not hardware limited, I'll just keep trying to find an emulator version that works for these non-standard refresh rate games.

Would you recommend a Pi4 upgrade at this point? Would you say your software release for the 4 is comparable to the 3.x feature set?

dee2eR
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Re: Pi 3+: fixed pixel clock?

Post by dee2eR » Thu Apr 01, 2021 3:16 am

At this point ARpiCADE on Pi4 is nearly at feature parity with ARpiCADE 3.X on Pi3. It's currently missing Daphne (will 100% be in the next release though), C64 and Amiga (maybe something else too, I'd have to check as I'm mainly worrying about the arcade side of things at the moment) but has Naomi/Atomiswave which Pi3 doesn't (Naomi and Atomiswave arn't quite perfect but are very good and generally fullspeed - very playable). There are still some Pi4 quirks to be worked out, eg. the splash screen doesn't start up straight away so some boot text may be visible and I haven't made a high res config for it yet so it's low res only at the moment.

Another change is the Pi4 has inbuilt firmware on a chip (earlier models didn't and booted purely off the SD card), which could add another level of complexity. I have updated my Pi4s (all early examples of Pi4 so newer ones may be fine out of the box) as the firmware they came with used more power and heated up the Pi more. ARpiCADE 4.2 has the firmware I used in /home/pi/ just in case... pretty sure it fixed my Pi4 2 gig which was very unstable out of the box but now seems to work OK.

Long term Pi4 is almost certainly the way to go. Right now, Pi4 as an upgrade may be worth it for you. Pi4 (using MAME 0.172) definately runs MK3 better than Pi3, while it's fullspeed on Pi3 (in 078) it's not perfect, as you have seen. At the moment Pi3B+ is much better tested and has fewer bugs but Pi4 is pretty good and has the power to run a lot of things in newer MAME versions (compared to Pi3) for better quality emulation (assuming it has been improved in some way in the newer version of MAME). Also MAME 172 (and 203) has genuine next frame response, where AdvMAME and the Retroarch based MAME cores have 1 extra frame of input handling, so being able to use 172 instead of 078 or 106 can also improve that side of things.

mbsalles
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Re: Pi 3+: fixed pixel clock?

Post by mbsalles » Thu Apr 01, 2021 3:56 am

Gotcha and agreed on all counts. I'll look into a Pi 4 upgrade soonish and will be getting another RaspberryJamma for my vert cabinet, it's just amazing on all counts.

Great job and thanks again for all your hard work.

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