PSP Rhythm has been updated after a while. It is a drum machine for the PSP. Notes:

Version 2.0 has been directly influenced by one of our favorite modern drum machines, the Elektron MachineDrum. The most significant change between ver. 1.5 to 2.0 is our use of”parameter locks”(as used by the MachineDrum). Parameter locks enable you to change the pitch, volume, and pan per step to create moving, changing melodies and effects. This control over your sounds will give you much more creative freedom and allow you to not only use drums, but to use instruments in your music. Song Mode has been enhanced with a mixer function, allowing you even more versatility with your song writing. The user interface has been made more intuitive and easy to use

http://www.iturzaeta.com/PSPRhythm/