Homebrew PSP plugin to persistently lock the CPU clock to a specific speed?

2excal7 · May 9, 2024

I was playing Trails In The Sky, and I used CWCheat to set the CPU speed to 111 Mhz because it just so happens the game isn't all that intensive to run and I wanted to be able to reduce the battery consumption. But then I noticed the CPU clock kept getting reset to the default 222 MHz... at first I was confused why it did that, figured that maybe the game just refuses to run in any speed other than 222 MHz.

But then I had a thought.... so I had my character enter a new map, and I brought up CWCheat as the screen was fading out and sure enough, I noticed the clock had been bumped to 333 MHz. And then afterwards when the new map's done loading, the CPU clock speed was back at 222 MHz. So in other words, the CPU clock is temporarily bumped up anytime the game enters a loading state to speed up loading times, then back down when it's done. This is not exactly an issue in and of itself, but it does mean that I can never run the game at anything other than 222 MHz.

So now that I know the game does this, does anyone know if there's a plugin that can persistently keep the CPU clock to the speed I want?

slaphappygamer · May 9, 2024

I’ve always changed the clock speed in the recovery menu. I did this with GTA Vice City Stories and it worked well. I had the speed set to 333mhz. I like the recovery menu options better since I can GAME and XMB independently.

2excal7 · May 9, 2024

Welp, I dug out ye olde PPSSPP disassembly tool and decided to take matters into my own hands: I stubbed out the function calls responsible for changing the clock speed during gameplay.

It happens at at least 6 different instances:

When the game is booted (clock up)
When you reach the title menu (clock down)
When you start/load a game (clock up)
When the game finishes loading (clock down)
When you enter a different map (clock up)
When the map finishes loading (clock down)

Instance #1 happens way too early and CWCheat hasn't even loaded by this point, so I left it out. I only stubbed the other 5 instances where it matters. This here's for the official English release of the game - I've tested it and so far the clock speed has stayed put, just as I wanted.

Code:

_S ULUS-10540
_G Trails In The Sky [USA]
_C1 Disable clock speed change
_L 0xE00A9267 0x00004D6C
_L 0x20004D6C 0x00000000
_L 0x20004D70 0x00000000
_L 0x20107304 0x00000000
_L 0x20107308 0x00000000
_L 0x20107A94 0x00000000
_L 0x20107A98 0x00000000
_L 0x201085DC 0x00000000
_L 0x201085E0 0x00000000
_L 0x20108CE4 0x00000000
_L 0x20108CE8 0x00000000

I'm still looking for a plugin that locks it persistently so I wouldn't need to do all this. I still have the Second Chapter to look forward to after all.

Homebrew PSP plugin to persistently lock the CPU clock to a specific speed?

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