Afterdawn has written a guide to learn people how to downgrade the firmware of their Sony PlayStation Portable from version 2.0 to 1.5 in order to be able to run homebrew applications.
Before we get on the to screenshots and bad quality photos i managed to capture of the process, I thought it would be good to give a small idea of what exactly has to be done. Firstly, this all started with the toc2rta exploit. An known issue discovered with the photo viewer led to the first homebrew code to be run on a PSP, and all it did was colour the screen. That was enough, it was simple proof of concept and without it, there wouldn't be a working downgrader now.
What had to be done originally was simple. You had two files, frame_buffer.png and overflow.tif. You had to transfer the frame_buffer.png file to the PHOTO folder on your Memory Stick and set it as the background (had to activate background in the theme settings). Then you had to add overflow.tif to the PHOTO directory. Now when you went to view photos the screen got coloured with a sort of yellow/light brown colour. Later on more stuff showed up for it, including the first working homebrew game; Tif Pong..