MiSTer FPGA Forum

Does anyone with the knowledge of vintage arcade games know if the analog video output of Tapper in MiSTer is accurate? The core outputs 240p image with noticeable flicker on sprites. From my understanding the game combines 240p and 480i assets into one image, with sprites being noticeably more detailed than the background graphics. Should the core output 480i video or is the current 240p resolution actually correct?

If I remember right, the core has the option to output at VGA resolution (640x480), or native 15k 480i. Original Tapper hardware is 15k 480i, so if you are getting 240p that doesn't sound right.

Currently the core outputs video with the these specs: 511x240, 15.78KHz, 59.7Hz. The picture is clearly in progressive scan with blank scanlines every other line. The core also has an option titled "Deinterlacer Hi-Res" which, I assume, turns the video from 240p to 480p, making it lose sync on 15KHz TV.

511x240 is interlaced, otherwise it would be a 2:1_ish aspect ratio. Interlaced video on MiSTer often reports that way. Interlaced IS basically 240p but it's alternating which lines it draws the 240 lines on vertically.

aberu wrote: ↑Wed May 17, 2023 12:02 am

511x240 is interlaced, otherwise it would be a 2:1_ish aspect ratio. Interlaced video on MiSTer often reports that way. Interlaced IS basically 240p but it's alternating which lines it draws the 240 lines on vertically.

480 is the interlaced output shown in the OSD, not 240 (as long as we’re talking about HDMI output). EDIT: I may have had Deinterlacer Hi-Res set to ON. In the Amiga core, it reports this with an i to indicate interlaced in 15kHz, maybe that’s not the case here?

That being said, my Tapper core reports 511×480 (31kHz, 60hz) and looks great, so maybe something else is going on? Maybe not supplying the proper 480i signal on the analog output? I don’t have an analog display handy right now, maybe it only works with 31kHz as implemented, and does not do 480i at 15kHz?

It could be similar to the Sega Genesis core when playing Sonic 2 in 2-player, where it's not "true" interlaced. that game specifically doesn't output interlaced to the TV, it outputs 240p while the game appears like it's interlaced.

Mister reports that mode as 448i, so something thinks it is interlaced

aberu wrote: ↑Wed May 17, 2023 4:47 pm

It could be similar to the Sega Genesis core when playing Sonic 2 in 2-player, where it's not "true" interlaced. that game specifically doesn't output interlaced to the TV, it outputs 240p while the game appears like it's interlaced.

Hi,
Most 1980s displays are 15Khz. It is around 263 lines per frame with around 240 visible lines. 1 picture is made of 2 frames with interlaced content. Early arcade games use the same content for both frames, this ease the 31Khz (480 visible lines) conversion with very simple line doubler.

Such scan/line doubler cannot convert true interlaced video of MCR1/2/3 games (tapper, ...) especially for sprites. It required a deinterlacer which take care of odd/even frames. Such a good deinterlacer is available with MiSTer.

To get a correct display on MiSTer you either have to activate the deinterlacer for 31Khz mode or use the 15Khz native mode.

So, as I understand, MCR3 is a true interlaced video system (480i), and MiSTer core outputting progressive 240p video on analog display is an imperfection of the core?

TLPD-AVW wrote: ↑Sun May 28, 2023 8:34 pm

So, as I understand, MCR3 is a true interlaced video system (480i), and MiSTer core outputting progressive 240p video on analog display is an imperfection of the core?

Yes and no. 480i and 240p refer to a digital standard. Obviously MCR systems do not carry those, but they do use a different interlacing technique to get a kind of 'super-hires' mode for some graphics on a standard res 15Khz monitor. (which was sometimes done on other systems as well)
Somehow this interlaced mode does not translate well on analogue out on MiSTerFPGA indeed. The original boards do not have the shimmering artefacts for sure!
Cores affected include: Discs of Tron, Two Tigers, Spy Hunter (which has scrolling issues too), Tapper, Timber, Journey, Rampage, Sarge.. etc.

I suppose the reason lies somewhere in the MiSTer main framework, which was never built to cater for CRT output. I am sure someone with some better knowledge could explain it better.

I have a Wells Gardner 27d9200 tri-sync arcade monitor in my MiSTer Cabinet. If I run Tapper at native resolution ("vga_scaler=0") out of the VGA port on the IO board, I get the following output from MiSTer, based on what my monitor reports:

• With "De-Interlacer Hi-Res: Off", MiSTer banner reports 511x240 15.78KHz, 59.7Hz. My monitor reports 15.6KHz / 59Hz.
  This is an interlaced frequency - it's drawing each alternating row 30 times per second (256 rows), instead of every row (511 rows) 60 times per second. I can see the flickering of some elements on the screen.

• With "De-Interlacer Hi-Res: On",MiSTer banner reports 511x240 31.56KHz, 60,1Hz. My monitor reports 31.3KHz / 60Hz - This is a hi-res progressive frequency, each line (511) is drawn 60 times per second. Nice solid hi-res display.

My recollection is the original game supported the interlaced mode for use with conversion kits on existing 15KHz monitors, but also shipped with 31KHz hi-res monitors as well, hence the configurability.

I would say the core is accurate, as there would be no way to display the hi-res sprites without using an interlaced mode on 15KHz arcade monitors.

retrodroid wrote: ↑Tue Sep 19, 2023 12:58 am

I have a Wells Gardner 27d9200 tri-sync arcade monitor in my MiSTer Cabinet. If I run Tapper at native resolution ("vga_scaler=0") out of the VGA port on the IO board, I get the following output from MiSTer, based on what my monitor reports:

• With "De-Interlacer Hi-Res: Off", MiSTer banner reports 511x240 15.78KHz, 59.7Hz. My monitor reports 15.6KHz / 59Hz.
  This is an interlaced frequency - it's drawing each alternating row 30 times per second (256 rows), instead of every row (511 rows) 60 times per second. I can see the flickering of some elements on the screen.

• With "De-Interlacer Hi-Res: On",MiSTer banner reports 511x240 31.56KHz, 60,1Hz. My monitor reports 31.3KHz / 60Hz - This is a hi-res progressive frequency, each line (511) is drawn 60 times per second. Nice solid hi-res display.

My recollection is the original game supported the interlaced mode for use with conversion kits on existing 15KHz monitors, but also shipped with 31KHz hi-res monitors as well, hence the configurability.

I would say the core is accurate, as there would be no way to display the hi-res sprites without using an interlaced mode on 15KHz arcade monitors.

Hi retroidroid, you've made a mistake in your testing - 511 is the horizontal resolution not vertical. 240 is the number of rows.

I fix MCR boards so I'm a bit familiar - the sprites on Tapper are interlaced while the backgrounds are not. There is no 31kHz mode on the arcade board. 31kHz monitors wouldn't be in arcades until 1991.

I took a picture of my arcade CRT hooked up to my MiSTer via the analog board VGA, wit a 1/30 shutter speed so it would capture both interlaced fields if it was drawing it. You can clearly see that it actually just draws 240p with clear scanlines.

However, the sprites do flicker in place for some reason. I don't know what's up with that.

callanabrown wrote: ↑Tue Sep 19, 2023 12:42 pm

Hi retroidroid, you've made a mistake in your testing - 511 is the horizontal resolution not vertical. 240 is the number of rows.

Of course you are correct.

When the game is set to "De-Interlacer Hi-Res: On" it must be outputting 511 x 480, since it uses the 31KHz mode lacks visible scan-lines or flickering.