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March33 Driver

The Epinephrine March33 2 driver is an evolution of the March33 Driver of the classic, and very popular, M33 CFW.

Evolution of the driver

The March33 driver was originally developed by the M33 Team for their custom firmware M33 CFW. The detailed evolution of the driver can’t be known besides release notes from the M33 CFW, as back in the day, closed-source development was the norm, and, according to Dark_AleX, the team had other reasons to maintain their software closed-source. So let’s do a quick dive and try to give an idea of the evolution of this driver. We will start with 3.51—M33-3, which was the debut of the driver. The following version is a ludic version number; we will consider all reported changes as the last release of the same base OFW version.

  • March33 1.0: The original March33 driver. Debuted on 3.51—M33-3 in July 2007. It had support for ISO and CSO image formats and was the version that the later version of M33 CFW would improve upon.
  • March33 1.1: An natural evolution fo the March33 driver. Released in 3.51—M33-7, in the same month as the 1.0. The release changelog indicated improved loading speed of ISO and CSO.
  • March33 1.2: Pretty much only bug fixing and some compatibility improvements. Released on 3.71—M33-3 in November of the same year.
  • March33 1.3: Increased compatibility with games and bug fixes. Released on 3.90—M33-3 in March of 2008. There were no further notable mentions in the changelogs of versions after this one. This release is the most important as it is the version that was open-sourced years later, in 2017, after all members of the team agreed to release it.
    • Since there were no further notable mentions on the changelogs, we are considering the binary version used on later CFW is this one, or very close to it, patched to work on later versions of the PSP Firmware.
    • The Epinephrine version was initially based on this version.
  • March33 RE: A reverse-engineered version of the March33 driver made available in the ME CFW with added support for the DAX image format.

Now that we’ve covered the history and evolution of the March33 Driver over the years, we can focus on the changes made to it in EPI that justify it being called March33 2.

  • Support for other compressed formats: The new reader was also made to be easily configurable and expandable to support other formats, having been given support for not only CSO and ZSO, but also adds support for DAX as seen on ME’s March33 update, as well as the rarely seen before JSO and CSOv2 formats. The driver also supports different block sizes, with 2K and 8K being more common (the higher the block size, the better the compression, but also the more memory used by the driver and thus less available for plugins). All formats benefit equally from the speedup hacks, meaning that performance is mainly left to the decompression algorithm they use.
  • Emulation of Empty UMD Drive: On older versions of March33, as well as other ISO Drivers except Inferno 2, it was never intended for the driver to run without an ISO file to be mounted, thus several bugs existed that caused malfunction when the driver was used without an ISO file specified, this prevented emulation of an empty UMD drive, which was needed on PS Vita to run certain homebrew that checked for a UMD. The main bug was in the implementation of the function sceUmdCheckMedium, a boolean function used to check if a UMD is inserted in the drive, on ISO driver this function was hardcoded to always return true, except if an ISO driver is not specified, then it was hardcoded to wait in an infinite loop until one is (which never happens). The solution used by eCFW such as ARK (up to ARK-3) and TN-CEF (including Adrenaline) was to include a small dummy fake.cso file to mount when no ISO file is specified. On the new March33 2 driver, among other things, this function has been corrected to behave exactly like the original, simply returning False if no ISO has been specified, thus allowing the ISO driver to simulate an empty UMD drive by loading it without an ISO file specified.
  • Improved Compressed ISO Read Speeds: Not only is the algorithm written with efficiency in mind, it also implements a more aggressive form of the speedup hacks.
  • Physical UMD seek and read time simulation: Configurable option to simulate the seek time and read time of reading a physical UMD to bypass the anti-CFW checks of some games, or fix games with synchronization issues due to faster read times.