axi_test: Optionally randomize responses

This patch makes it optional for a random slave to randomize the success
of any accesses. The default is off, so any existing code should be
still compatible.

Again, useful for achieving code coverage on error conditions of any
modules.

CHANGELOG.md

@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Added
 - `typedef.svh`: Add `AXI_TYPEDEF_ALL` macro for defining all channels and request/response
   `struct`s in a single macro call.
+- `axi_test::axi_rand_slave`: Add parameter `RAND_RESP`, which enables randomization of the `resp`
+  field in B and R beats.
 
 ### Changed
 - `axi_test::axi_rand_master`: Randomize the QoS field.

src/axi_test.sv

@@ -1177,6 +1177,7 @@ package axi_test;
     // Stimuli application and test time
     parameter time  TA = 0ps,
     parameter time  TT = 0ps,
+    parameter bit   RAND_RESP = 0,
     // Upper and lower bounds on wait cycles on Ax, W, and resp (R and B) channels
     parameter int   AX_MIN_WAIT_CYCLES = 0,
     parameter int   AX_MAX_WAIT_CYCLES = 100,
@@ -1250,6 +1251,8 @@ package axi_test;
         ar_beat = ar_queue.peek();
         rand_success = r_beat.randomize(); assert(rand_success);
         r_beat.r_id = ar_beat.ax_id;
+        if (RAND_RESP && !ar_beat.ax_atop[axi_pkg::ATOP_R_RESP])
+          r_beat.r_resp[1] = $random();
         if (ar_beat.ax_lock)
           r_beat.r_resp[0]= $random();
         rand_wait(R_MIN_WAIT_CYCLES, R_MAX_WAIT_CYCLES);
@@ -1300,6 +1303,8 @@ package axi_test;
         aw_beat = aw_queue.pop_front();
         rand_success = b_beat.randomize(); assert(rand_success);
         b_beat.b_id = aw_beat.ax_id;
+        if (RAND_RESP && !aw_beat.ax_atop[axi_pkg::ATOP_R_RESP])
+          b_beat.b_resp[1] = $random();
         if (aw_beat.ax_lock) begin
           b_beat.b_resp[0]= $random();
         end