Investigate increased througput of the TRNG

[dehanj]

The current TRNG has a defined sample cycle to sample every 1000th clock tick, currently giving 21 kHz (or 18 kHz in the latest release). It might be possible to increase the throughput, by sampling more often, without lowering the quality.

It needs however to be investigated, dumping out large amounts of data and running it through relevant tools (such as PRACTRAND and ENT) to see if there is a difference.

in rosc.v

  localparam SAMPLE_CYCLES = 16'h1000;