Moar hardware: Retro Scaler A1

invzim · **Posted:** Mon Jan 13, 2020 5:27 pm

fernan1234 wrote:

I'd really like to check out one of these scalers. I know it was designed primarily for arcade boards, but it lists support for 480i/576i, so I'm wondering how interlaced 15khz looks like scan converted to the 31khz output. Does it look like the well-regarded de-interlaced output of the Micomsoft scalers, or maybe even better? And are in-game resolution changes (especially 480i<-->240p) handled without sync drops by this scaler?

Interlace is tbh not the A1's strong suit, it just line doubles the input - so depending a bit on the source, it will look wobbly. My XRGB2 combines the fields and displays the resulting 480 frame very nicely, but you need a framebuffer to do that.
240p test suite on dreamcast looks good though.

As the line-count changes when it switches from 480i to 240p, it will resync. I haven't tested it with instruments - but with a CRT and the 240p test suite, it's about 1 second - you can see it in the video I posted a while back, https://youtu.be/MUx4QuohGdg?t=179

orange808 · Joined: 20 Aug 2016 Posts: 1438

invzim wrote:

fernan1234 wrote:

I'd really like to check out one of these scalers. I know it was designed primarily for arcade boards, but it lists support for 480i/576i, so I'm wondering how interlaced 15khz looks like scan converted to the 31khz output. Does it look like the well-regarded de-interlaced output of the Micomsoft scalers, or maybe even better? And are in-game resolution changes (especially 480i<-->240p) handled without sync drops by this scaler?

Interlace is tbh not the A1's strong suit, it just line doubles the input - so depending a bit on the source, it will look wobbly. My XRGB2 combines the fields and displays the resulting 480 frame very nicely, but you need a framebuffer to do that.
240p test suite on dreamcast looks good though.

As the line-count changes when it switches from 480i to 240p, it will resync. I haven't tested it with instruments - but with a CRT and the 240p test suite, it's about 1 second - you can see it in the video I posted a while back, https://youtu.be/MUx4QuohGdg?t=179

Interesting...

My XRGB2 does simple bob deinterlacing.

invzim · **Posted:** Mon Jan 13, 2020 5:35 pm

I haven't tested it extensively, but it does the right-thing in the iconic ST-V title Winter Heat

Fudoh · Joined: 06 Mar 2006 Posts: 11975 Location: Germany

Quote:

My XRGB2 does simple bob deinterlacing.

it adds a line offset to the odd fields though, shifting the fields slightly towards each other.

Ryoandr · Joined: 12 Jun 2017 Posts: 174

orange808 wrote:

Also, the MiSTer scaler seems to pull the Neo Geo MVS frame rate up to around 59.7Hz. The OSSC doesn't report frame rates perfectly, but I'm pretty sure MiSTer is changing the frame rate. I could be wrong.

A real MVS board reports 59.18Hz. The direct MiSTer analog output for MVS (without the scaler) also returns 59.18Hz.

59.7 might be related to AES, as it uses a slightly higher crystal to be closer to NTSC rate. Maybe MiSTer went with that.

orange808 · Joined: 20 Aug 2016 Posts: 1438

Ryoandr wrote:

orange808 wrote:

Also, the MiSTer scaler seems to pull the Neo Geo MVS frame rate up to around 59.7Hz. The OSSC doesn't report frame rates perfectly, but I'm pretty sure MiSTer is changing the frame rate. I could be wrong.

A real MVS board reports 59.18Hz. The direct MiSTer analog output for MVS (without the scaler) also returns 59.18Hz.

59.7 might be related to AES, as it uses a slightly higher crystal to be closer to NTSC rate. Maybe MiSTer went with that.

Nope. It's the OSSC that had me fooled.

I hooked up an old Extron RGB unit that also reads signal information and it sees the refresh rate at 59.19Hz with the scaler enabled. The OSSC gets funny results. Signal information on the OSSC isn't always reliable, so it's my fault for trusting it.

Fudoh had it right all along.

marqs · Joined: 15 Dec 2012 Posts: 712 Location: Finland

Fudoh wrote:

Quote:

MiSTer has an interesting pixel clock trick that might show promise for better frame rate conversion in a future device.

either I don't understand what he's writing or that's about the silliest text I've ever read to describe a workaround that isn't really a workaround in the first place.

What he describes has been done to frame lock output refresh rates since digital video transmission existed. Timing parameters remain to spec with just the refresh being locked to the input (or emu core in this case). This naturally adjusts the pixel clock slightly up or down depending on the target refresh rate.

So, yes, it's good that frame lock is available on MISTer, but what's the big deal?

I wouldn't call that mode framelock as frames get dropped/duplicated, even if it happens once in a hour (which also means that half of that time has at least 1/2 frame of latency). I recall MISTer having a true framelock mode (vsync_adjust=2) for at least some cores, but for some reason it's not documented on that page

orange808 wrote:

I hooked up an old Extron RGB unit that also reads signal information and it sees the refresh rate at 59.19Hz with the scaler enabled. The OSSC gets funny results. Signal information on the OSSC isn't always reliable, so it's my fault for trusting it.

OSSC's refresh rate information on the main screen is based on measurement data from video ADC which is not always accurate. FPGA provides an accurate measurement which can be checked from info screen (divide 27000000 by the reported number to get Hz).

Speaking of video ADCs, it'd be interesting to make a comparison between the chips in OSSC (TVP7002) and A1 (AD9984A). AD9984A was actually a candidate for OSSC when it was originally designed, but I ended with TVP7002 as it had CSC block and 3:1 input mux (the 3rd input wasn't used in the end, though).

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Moar hardware: Retro Scaler A1

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