Higher V. Backporch Support for Optimal PSP In-Game Picture

[eatnumber1]

I’m looking to dial in some optimal PSP settings. I’ve calculated some optimal timings based on hooking up my PSP to an oscilloscope, and am able to get a nice picture when in the main menu.

Unfortunately however, the PSP letterboxes games. If I treat the letterboxed area as H./V. frontporch and backporch, I’ve calculated what the correct H/V. Active and H/V. Backporch should be. Unfortunately, the V. Backporch setting doesn’t go high enough (max is 63, I want 134). Is it possible to increase that limit?

Here is my timing measurements, along with the calculations with the resulting OSSC settings.

[BuckoA51]

I’m not sure many displays could tolerate that high, but I couldn’t say for sure.

[eatnumber1]

As far as I know, the OSSC will adjust the frontporch to compensate, and won’t adjust the V. Active region, meaning that the resulting output resolution won’t change, so TVs should see little to no difference.

I’m already running the PSP with a 480p input signal, but the active/backporch regions configured so that the resulting output image is 640×360.

At V. Backporch = 134 and V. Active = 272, the OSSC will be perfectly outputting only the actual non-letterboxed portions of the screen. That said, the resulting image will be 480×272, or 960×544 in line2x, which probably won’t work (or at least look good) on my TV. That said, if I allow for some amount of letterboxing and bump the V. Active up to 360, the V. Backporch needed to center the image on screen is 86 (still higher than the current 63). Alternatively, if I cut off two real pixels from the vertical resolution (V. Active = 270), I’ll get a 480×270 picture, which in line2x is 960×540, which is a standard resolution (qHD). I think that doing so will require a V. Backporch of 135. In fact, here’s the PSP with those settings (V. Active = 270, H. Active = 480). It scales decently well to my 4k display horizontally, and should also vertically, but cuts off on the bottom without being able to set V. Backporch to 135.

Here’s how that looks:

[eatnumber1]

I have implemented this, and marqs has merged my changes. It will be released with the next version of the OSSC firmware (0.86). Here’s how it looks, and I’ll put the settings I’m using below the screenshots.

I believe the remaining blurring is due to my TV’s poor upscaling, along with some analog video noise coming from the PSP itself.

The settings I’m using are:
H. Backporch: 176
H. Active: 480
V. Backporch: 135
V. Active: 270

Oddly, these backporch values are not the ones I’d calculated, but these are the ones that produce a centered image.

Now, with a 960×540 image, 2x that would be 1920×1080 (1080p). Time to dig into whether a Line4x in 480p mode is possible to implement :).

[BuckoA51]

Excellent work 🙂

[nmalinoski]

This is really cool. Is there a facility for automatically detecting when the PSP goes into game mode (resolution switch?), or will there be profile swapping involved?

[eatnumber1]

Sadly no, or at least it’s not straightforward. There’s no resolution switch as far as the OSSC (or your TV) is concerned.

However that said, I improved on this further since my last post, and 0.86 now has a dedicated sampling mode and an optimized line2x mode. So all you need to do is set “480p in sampler” to “PSP 480×272”.

It might be possible to count the size of the overscan area plus the letterbox and switch when the active region changes, but I’m not sure if that will be prone to false triggering in other places though.

Also FYI I looked into line4x. It’s not possible at all, ever on the OSSC (maybe the pro, idk). The HDMI transmitter cannot run at a fast enough clock speed. That said, I did some work to get the OSSC working better at clock speeds close to its theoretical max so that I can do line3x with a 3x vertical and 2x horizontal pixel clock (3x horizontal is also too fast). That work also got released with 0.86, although the Line3x mode is disabled because it’s not aspect ratio preserving. With those settings, it’s at the edge of what the OSSC can support, but it now works. With 2x horizontal, there’s enough room in the overscan area now that I can theoretically get to 3x horizontal without increasing clock speed by drawing into the overscan. The OSSC doesn’t support that kind of drawing mode yet though, so implementing that support is my next project. Once it works the output resolution should be 1440×816.

[tylerfox3894]

i know i am a little late to the party on this one. i downloaded the update 0.86. set it to psp mode, and i get no picture whatsoever. i am a total noob when it comes to advanced settings on the OSSC, can anyone help me figure out what i am doing wrong?

[Harrumph]

Your display is likely not compatible.

[eatnumber1]

Handled in https://videogameperfection.com/forums/topic/psp-help-for-a-total-noob/. We hypothesized that their TV doesn’t support more than 203 offscreen lines.

[triple_lei]

So I’m far from am expert at OSSC fine-tuning, but playing Final Fantasy Tactics: War of the Lions and using the “FFT Slowdown Fix and Unstretch Screen Patch” (the latter of which shrinks the resolution of the game from 480×272 to 320×240), and then using my TV’s zoom feature, I’ve found that setting Sampling Phase to 0 deg (or 348 deg!) in addition to eatnumber1’s settings’s makes things pretty sharp. This is all with 480p Line 2x, of course.

The game’s tiny text, made tinier by the patch, is so much easier to read, and eyes look like eyes again. Also sharpens the tiny text in Baito Hell 2000, which of course never had any such unstretch patch.

I can’t really tell if 0 deg or 348 deg is more centered though. 0 deg seemed more centered.

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