test: Debug timestamp high-low feature test.

Keep bit 31 of generated TS equal to 0. This is to avoid
overflow on numeric conversion of 31 bit unsigned vector
to natural.

test/feature/timestamp_low_high_feature_tb.vhd

@@ -102,11 +102,18 @@ package body timestamp_low_high_feature is
         -- Force random timestamp so that we are sure that both words of the
         -- timestamp are clocked properly!
         rand_logic_vect_v(rand_ctr, ts_rand, 0.5);
+        
         -- Keep highest bit 0 to avoid complete overflow during the test!
         ts_rand(63) := '0';
 
-        ftr_tb_set_timestamp(ts_rand, ID_1, so.ts_preset, so.ts_preset_val);
+        -- Additionally, keep bit 31=0. This is because timestamp is internally
+        -- in TB implemented from two naturals which are 0 .. 2^31 - 1. If we
+        -- would generate bit 31=1, conversion "to_integer" from such unsigned
+        -- value is out of scope of natural!
+        ts_rand(31) := '0';
+
         info("Forcing start timestamp in Node 1 to: " & to_hstring(ts_rand));
+        ftr_tb_set_timestamp(ts_rand, ID_1, so.ts_preset, so.ts_preset_val);
 
         wait for 100 ns;