GSM Reference

GSM — forced video modes

GSM makes a game output a video mode it was never written to output. Most PS2 games render 480i (or 576i in PAL). GSM intercepts the game's video setup and substitutes a different raster, so the same game can come out as 480p, 720p, 1080i, or one of a range of VGA modes — useful on modern displays and upscalers that handle interlaced signals badly or not at all.

GSM does not re-render anything. The game still draws the same picture at the same internal resolution; GSM changes how that picture is scanned out. Expect a cleaner, more stable signal, not extra detail.

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Where to set it

GSM lives in two places:

• Per game — Triangle on a title → Configure GSM.
• Globally — GSM Defaults (All Games) on Settings → Game Launching (also on Interface and General & System). This is what every game with no GSM settings of its own inherits.

The per-game page's first row, Settings Mode (stored as $GSMSource), decides which of those wins:

Settings Mode	Meaning
Global	Ignore this game's GSM keys entirely and follow the global defaults. Selecting it also removes the game's stored GSM keys.
Per Game	This game's GSM settings apply, as a complete set.
Per Game + Global	Per-key inheritance: any GSM value this game sets is used, and anything it leaves unset falls through to the global default.

Per Game + Global is the option to reach for when you want one game to differ from your global setup in a single respect — a different video mode, say — while still tracking your global choices for everything else.

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The options

Option	What it does
GSM Selector	The on/off switch. With it off, the four rows below are greyed out and GSM does nothing.
Forced custom display mode	The video mode to output. See the list below.
H-POS	Horizontal position offset, −100 to +100. Shifts the picture left/right.
V-POS	Vertical position offset, −100 to +100. Shifts the picture up/down.
Emulate FIELD Flipping	Compatibility fix for games that shake, tear, or judder under a progressive mode. Try this first when a game looks wrong after GSM is applied.

On the per-game page the mode list ends with Default, which means "follow the global setting". Picking it removes the key rather than storing a value, so the game genuinely tracks the global from then on. That entry does not appear on the global page, where it would be meaningless.

Available modes

Modes 0–5 are the standard console rasters; the rest are forced progressive, HDTV, or VGA modes.

#	Mode		#	Mode
0	NTSC		15	VGA 640x480p @75Hz
1	NTSC Non Interlaced		16	VGA 640x480p @85Hz
2	PAL		17	VGA 640x960i @60Hz
3	PAL Non Interlaced		18	VGA 800x600p @56Hz
4	PAL @60Hz		19	VGA 800x600p @60Hz
5	PAL @60Hz Non Interlaced		20	VGA 800x600p @72Hz
6	PS1 NTSC (HDTV 480p @60Hz)		21	VGA 800x600p @75Hz
7	PS1 PAL (HDTV 576p @50Hz)		22	VGA 800x600p @85Hz
8	HDTV 480p @60Hz		23	VGA 1024x768p @60Hz
9	HDTV 576p @50Hz		24	VGA 1024x768p @70Hz
10	HDTV 720p @60Hz		25	VGA 1024x768p @75Hz
11	HDTV 1080i @60Hz		26	VGA 1024x768p @85Hz
12	HDTV 1080i @60Hz Non Interlaced		27	VGA 1280x1024p @60Hz
13	VGA 640x480p @60Hz		28	VGA 1280x1024p @75Hz
14	VGA 640x480p @72Hz		29	HDTV 1080p @60Hz (EXPERIMENTAL)

HDTV 480p @60Hz (8) is the safe starting point on almost any modern display. 720p (10) and 1080i (11) are the next most widely accepted. The VGA modes need a display fed over VGA or a component/VGA-capable path; a plain HDMI adapter will usually not sync them.

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1080p is experimental, and asks three times

Mode 29, HDTV 1080p @60Hz (EXPERIMENTAL), is compiled into every shipped build. It is a GSM-synthetic progressive raster — not a mode the PS2 hardware natively produces — and while it has passed real-hardware testing, it is non-standard enough that some displays will not sync it at all.

Because a display that cannot sync leaves you with a black screen and no way to undo the choice from the console, selecting 1080p with GSM enabled triggers a three-step confirmation before it is written to disk. Decline at any of the three steps and the mode falls back to NTSC (mode 0), not to your previous selection — so if you cancel, set the mode you actually wanted before leaving the page.

The same gate applies on the global page, which carries the wider blast radius of the two: it is what every game without its own GSM settings inherits.

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When a game loses the picture

The RiptOPL menu never uses GSM, so whatever you set, you can always get back to the browser and undo it. Which setting to undo depends on where you set it.

If you set it for one game (Settings Mode = Per Game), only that title is affected:

1. Return to the browser — reset the console if the game has no picture at all.
2. Triangle on the affected title → Configure GSM.
3. Either turn GSM Selector off, or pick a more conservative mode (480p, or the game's native NTSC/PAL).

If you set it globally, every game that has no GSM settings of its own inherits it — so they can all lose the picture at once. That is the wider blast radius the 1080p confirmation warns about:

1. Return to the browser.
2. Settings → Game Launching → GSM Defaults (All Games).
3. Turn GSM Selector off there, or pick a conservative mode, and save.

A game whose Settings Mode is Per Game keeps its own settings and is unaffected by the global one, so fixing the global default will not repair a title you broke individually — check both if only some games are affected.

If the menu itself has no picture, that is not GSM — that is the global video mode setting. Hold Triangle + Cross while RiptOPL boots to force the menu to 480p progressive. See CONTROLS.md.

The game runs but looks wrong

Shaking, tearing, or juddering under a progressive mode — turn on Emulate FIELD Flipping. This is what it exists for.

Picture off-centre — adjust H-POS and V-POS.

Some scenes fine, others broken — a few games switch video mode mid-run (typically for FMVs). Those tend to be poor GSM candidates; try a less aggressive mode or leave GSM off for that title.

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GSM and the other cores

Neutrino does not use OPL's GSM. It has its own forced video mode handling, and the per-game Neutrino GSM Compatibility option is the equivalent field-flipping fix — "for games that shake or tear under a forced Neutrino video mode". Set it there rather than on the GSM page when the Loader Core is Neutrino. See NEUTRINO.md.

PS1 titles run under POPSTARTER or Ember and do not use OPL's GSM either. Modes 6 and 7 in the list above are named "PS1 NTSC/PAL" because of the raster they produce, not because they apply to PS1 games. See VCD.md.

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Related settings that are not GSM

Two settings are easy to mistake for GSM options:

• Overscan (Settings → Interface) trims the edges of the RiptOPL menu, not of games. It is a UI setting and is unrelated to the GSM H-POS/V-POS offsets.
• Video Mode (Settings → Interface) sets the mode the menu runs in. GSM never affects it.

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Notes for builders

Two names are involved, and they are not the same thing. GSM1080P is the Makefile variable; it defaults to 1, and when set the Makefile adds -DGSM_1080P — the preprocessor macro the code actually tests — to the EE build, and forwards GSM1080P=1 on to ee_core/Makefile.

So every shipped build has mode 29 and the list is a consistent 30 entries across published flavours. Building with GSM1080P=0 drops it and shortens the list.

In-game screenshots (IGS) require GSM to be enabled — see IGR.md.

File	Role
ee_core/src/gsm_api.c, gsm_engine.S, gsm_engine_adv.S	The GSM engine
src/guigame.c	The GSM settings page, the mode list, and the 1080p confirmation gate
src/dialogs.c	The six GSM dialog rows

See also

• CONTROLS.md — the boot recovery combo for a menu with no picture
• IGR.md — in-game screenshots depend on GSM
• NEUTRINO.md — the alternative core's own video handling

Related guide: GSM.

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Source: docs/GSM.md @ 3ce281b0793c.