entropy_generator

Generate one entropy lane from a noise source, decorrelator, health tests, and auto-tune.

Combines a TOTAL_LENGTH/TAPPED_LENGTH ring oscillator sampled on sample_clk_i with decorrelation and Repetition/APT/Markov tests.

Controls:

auto_tune_enable_i lets health failures retune detune through the tune FSM; detune_ro_i forces detune.
bypass_decorrelator_i and entropy_byte_mask_i configure the decorrelator; sample_clk_div_i sets its downsample.
test_enable_i and the limit/threshold inputs program the three health tests; window_wrap_pulse_i closes each window.

count_err_o is this lane's health-test counter-disagreement error.

Parameters

Table 1. Parameters
Name	Type	Default	Description
`TOTAL_LENGTH`	`int unsigned`	`17`	Full ring-oscillator stage count.
`TAPPED_LENGTH`	`int unsigned`	`13`	Stage count of the shorter feedback tap, used while detune is low.
`CLKDIV_WIDTH`	`int unsigned`	`24`	Downsample divider counter width.

Ports

Table 2. Ports
Name	Direction	Type	Description
`clk_i`	input	`logic`	System clock.
`rst_ni`	input	`logic`	Active-low asynchronous reset.
`sample_clk_i`	input	`logic`	Ring-oscillator sample clock.
`enable_i`	input	`logic`	Enables the noise ring oscillator and the decorrelator.
`auto_tune_enable_i`	input	`logic`	High lets the tune FSM drive the ring detune in place of detune_ro_i.
`detune_ro_i`	input	`logic`	Manual ring detune while auto-tune is off: high selects the full TOTAL_LENGTH feedback path, low the shorter tap.
`sample_clk_div_i`	input	`logic [CLKDIV_WIDTH-1:0]`	Decorrelator downsample period minus one, in clk_i cycles.
`bypass_decorrelator_i`	input	`logic`	High removes the decorrelator XOR feedback.
`entropy_byte_mask_i`	input	`logic [7:0]`	AND mask on each decorrelator output byte.
`test_enable_i`	input	`logic [2:0]`	Health-test enables: bit 0 repetition, bit 1 APT, bit 2 Markov.
`repetition_limit_i`	input	`logic [7:0]`	Repetition-count failure threshold.
`proportion_limit_1bit_i`	input	`logic [15:0]`	APT high threshold on the per-bit ones count per window.
`proportion_limit_lo_i`	input	`logic [15:0]`	APT low threshold on the per-bit ones count per window.
`markov_prob_01_threshold_i`	input	`logic [15:0]`	Markov high threshold on the per-bit 01/10 pair count per window.
`markov_prob_10_threshold_i`	input	`logic [15:0]`	Markov low threshold on the per-bit 01/10 pair count per window.
`window_wrap_pulse_i`	input	`logic`	Shared end-of-window strobe that evaluates and restarts the APT and Markov tests.
`noise_bit_monitor_o`	output	`logic`	Synchronized noise-source bit, for debug observation.
`test_status_o`	output	`logic [7:0]`	Health-test status byte, encoded as entropy_health_test status_o.
`entropy_byte_o`	output	`logic [7:0]`	Masked decorrelator output byte.
`entropy_byte_valid_o`	output	`logic`	Single-cycle strobe marking a new entropy_byte_o.
`count_err_o`	output	`logic`	Redundant-counter fault in this lane's health tests.