I've found a second exploit in Sony's version 2.50 PSP firmware. Other than using savedata, I've gone to using a music file, a video, and a web page. The web page, which contains a masked link, launches the music file. The music file, called system_plugin.at3, has some hidden hex values that will launch a file the PSP itself has. That is logged and when the launch is finished, the video, called update_plugin.mp4, will launch the 1.50 EBOOT. If this sounds complicated, then wait for a less complicated way to do this.
Yeah, you might want to wait I've been working on this since about a week after 2.50 came out. People who have upgraded have more trouble than the homebrew users, I tell ya.
I'm going to test it right now. Hope it works
I've made some pretty good progress on the downgrader. I got the 1.5 EBOOT to run, but it only got to about 84% when the 2.5 PSP... "realized" what was going on. The downgrade aborted, but I almost had it. I don't want to, but if I have to write to the flash MORE than I am RIGHT NOW, I will. I don't want to write to the flash more than I have to or someone will try something stupid and brick their PSP and I'll have more e-mails in my inbox than Microsoft's at the release of the XBOX 360 (with troubleshooting lol). Sorry I didn't update you guys earlier, but I'm working as hard as I can on this downgrader. Might be about two to three days and you will have 1.5 PSPs! man it got super close almost to 100%