There are 4 shares (sets) of 8 distinct ring oscillators. The output bitstream from each set has its own set of tests as described in Continuous Testing. These bitstreams are merged by a blender to produce a single stream of entropy.
The most efficient way to generate random data with minimal latency is to concatenate the ring oscillator output streams (the hardware default). However, these outputs can be blended to increase entropy. The blender can be configured to use different methods for entropy enhancement via the BLENDINGMETHOD field. XORLEVEL1 reduces 4×8 bits to 4 bits, while XORLEVEL2 further reduces the 4 bits to 1. Another blending option is the Von-Neumann debiasing algorithm (VONNEUMANN), which assumes the input bits are independent and identically distributed (IID), producing a likely uniform output. When the Von-Neumann debiasing method is selected, the XORLEVEL1 and XORLEVEL2 compression methods are applied first, then 00 and 11 bit pairs are discarded while 10 and 01 pairs are retained, with only the first bit of each retained pair being output.