Hold+ v3.5 by Torch:
http://forums.qj.net/showthread.php?t=146628

Hold+ v3.5

Tested on 5.00M33-4

This is a simple plugin I made a long time ago for my personal use. I just found the source code while going through some old stuff on my computer, so I thought I'd clean up the code a bit and release the plugin.

I realize that there are other plugins that feature similar functionality but I wrote my own because I wanted to be sure its coded optimally, as there are a few careless ways in which these functions can be improperly used (the point of this after all is to conserve battery life).

It does the following when the Hold switch is enabled:
* Switches off the LCD backlight.
* Switches off the actual LCD screen.
(This is important because the backlight and actual screen are two different things. You can have an image being displayed on the screen while the backlight is switched off, such that you can see the image if you use a flashlight. You can also have the screen switched off while the backlight still illuminates the powered off screen.)
* Underclocks the CPU to 60MHz
(Sony has changed the clock speed functions such that only certain combinations of speeds work correctly. Simply trying to underclock to arbitary values will result in the CPU simply running at the stock speed. I have verified that Hold+ successfully underclocks to 60MHz.)
* The original screen brightness and clock speed are restored when the Hold switch is released.
* Prevents the PSP from going into suspend mode if you accidently push the power switch too far when turning off Hold mode.
* Allows complete operation of the PSP controls with the display turned off.
* Turns off LEDs in hold mode. LEDs are flashed once in 30 seconds so that the PSP is not mistaken to be powered off.
* While in hold mode, allows the use of Left, Right, LTrigger, RTrigger, Volume and Start buttons, if you hold the Select button first. Useful to skip songs, pause etc.

Additional Features:
*Enables the 5th brightness level.