[entropy_src/dv] Reduce max delay for CS AES Halt IF in max rate test

This is useful to reduce the backpressure in the pipeline as this leads
to entropy bits being dropped eventually which the scoreboard cannot
handle at the moment.

Signed-off-by: Pirmin Vogel <[email protected]>

hw/ip/entropy_src/dv/env/entropy_src_env.sv

@@ -58,10 +58,13 @@ class entropy_src_env extends cip_base_env #(
     cfg.m_aes_halt_agent_cfg.agent_type          = push_pull_agent_pkg::PullAgent;
     cfg.m_aes_halt_agent_cfg.if_mode             = dv_utils_pkg::Device;
     cfg.m_aes_halt_agent_cfg.pull_handshake_type = push_pull_agent_pkg::FourPhase;
-    // When CSRNG has just started operating its AES, it may take up to 48 cycles to acknowledge the
-    // request.
+    // When CSRNG has just started operating its AES, it may take up to 48 cycles to acknowledge
+    // the request. When running ast/rng at the maximum rate (this is an unrealistic scenario
+    // primarily used for reaching coverage metrics) we reduce the max acknowledge delay to
+    // reduce backpressure and avoid entropy bits from being dropped from the pipeline as our
+    // scoreboard cannot handle this.
     cfg.m_aes_halt_agent_cfg.zero_delays = 0;
-    cfg.m_aes_halt_agent_cfg.device_delay_max = 48;
+    cfg.m_aes_halt_agent_cfg.device_delay_max = (cfg.rng_max_delay == 1) ? 8 : 48;
     // CSRNG drops its ack in the cycle after entropy_src has dropped its req.
     cfg.m_aes_halt_agent_cfg.ack_lo_delay_max = 1;