entropy_fifo

Buffer 32-bit entropy words in a fault-hardened synchronous FIFO.

Depth is DEPTH words with per-byte even parity on stored data and hardened read/write pointers via prim_fifo_sync_cnt Secure=1. Local mem[] storage supports parity checks and entropy-churn reads that need random access.

When entropy_churn_enable_i is set, pushes XOR with the existing entry at (wptr + DEPTH/2) % DEPTH before store. clr_i synchronously flushes pointers and level to empty.

security_alert_o rises on any parity or pointer error. Each fault class has its own output:

overflow_o
underflow_o
parity_error_o
pointer_error_o

Parameters

Table 1. Parameters
Name	Type	Default	Description
`DEPTH`	`int unsigned`	`64`	FIFO depth in words.

Ports

Table 2. Ports
Name	Direction	Type	Description
`clk_i`	input	`logic`	System clock.
`rst_ni`	input	`logic`	Active-low asynchronous reset of the pointers; the storage is not reset.
`push_i`	input	`logic`	Write request; ignored when full, on a pointer error or during clr_i.
`pop_i`	input	`logic`	Read acknowledge that advances the read pointer; ignored when empty, on a pointer error or during clr_i.
`clr_i`	input	`logic`	Synchronous flush: reset pointers/level to empty.
`wdata_i`	input	`logic [31:0]`	Entropy word stored on an accepted push.
`entropy_churn_enable_i`	input	`logic`	High XORs each pushed word with the entry half the FIFO depth ahead of the write pointer.
`rdata_o`	output	`logic [31:0]`	Head-of-FIFO word; zero while empty.
`level_o`	output	`level_t`	Number of stored words.
`wptr_o`	output	`ptr_t`	Storage index of the next write.
`rptr_o`	output	`ptr_t`	Storage index of the head entry.
`overflow_o`	output	`logic`	Push requested while full; the word is dropped.
`underflow_o`	output	`logic`	Pop requested while empty.
`parity_error_o`	output	`logic`	Head entry of a non-empty FIFO fails its per-byte even-parity check.
`pointer_error_o`	output	`logic`	Duplicated pointer counters disagree; pushes and pops are blocked while set.
`security_alert_o`	output	`logic`	OR of parity_error_o and pointer_error_o.