 On 28 February 2014, on the day of the second anniversary of the Raspberry Pi, Broadcom, together with the Raspberry PI foundation, announced the release of full documentation for the VideoCore IV graphics core, and a complete source release of the graphics stack under a 3-clause BSD license.However, only a minor part of the driver was released as open source; all of the video acceleration is done using a firmware coded for its proprietary GPU, which was not open sourced.The entire SoC itself is managed by a ThreadX-based RTOS that is loaded into the Videocore's VPU during bootup.