test: Add SSP_OFFSET correction to SSP_OFFSET feature test. Add random data bit time generation!

SSP_OFFSET cant be longer than data bit time! Otherwise, we are gonna
sample in the next bit and generate bit error way earlier than we
inject bit error to the bus.

test/feature/ssp_cfg_feature_tb.vhd

@@ -89,6 +89,7 @@
 context work.ctu_can_synth_context;
 context work.ctu_can_test_context;
 
+--Library ieee;
 use lib.pkg_feature_exec_dispath.all;
 
 package ssp_cfg_feature is
@@ -99,10 +100,47 @@ package ssp_cfg_feature is
         signal      mem_bus         : inout  mem_bus_arr_t;
         signal      bus_level       : in     std_logic
     );
+    
+    procedure correct_ssp_offset(
+       ssp_offset_generated         : in    std_logic_vector(7 downto 0);
+       bus_timing                   : in    bit_time_config_type;
+       ssp_offset_corrected         : out   std_logic_vector(7 downto 0)
+    );
+
 end package;
 
 
 package body ssp_cfg_feature is
+
+    ---------------------------------------------------------------------------
+    -- Data bit time is generated random. Also SSP_OFFSET is generated random.
+    -- We set real delay from CAN_TX to CAN_RX in TB also to random generated
+    -- value. If generated SSP_OFFSET is higher than duration of bit, then
+    -- we will never sample correct value, because we just sample next bit
+    -- already! So we need to constrain configured SSP_OFFSET to less than
+    -- data bit time!
+    --------------------------------------------------------------------------- 
+    procedure correct_ssp_offset(
+       ssp_offset_generated         : in    std_logic_vector(7 downto 0);
+       bus_timing                   : in    bit_time_config_type;
+       ssp_offset_corrected         : out   std_logic_vector(7 downto 0)
+    ) is
+        variable bit_time_length    :       natural;
+    begin
+        bit_time_length := bus_timing.tq_dbt * (1 + bus_timing.prop_dbt +
+            bus_timing.ph1_dbt + bus_timing.ph2_dbt);
+
+        if (to_integer(unsigned(ssp_offset_generated)) >= bit_time_length) then
+            ssp_offset_corrected := std_logic_vector(to_unsigned(bit_time_length - 1, 8));
+            info("Correcting SSP offset. Bit time length: " &
+                  integer'image(bit_time_length) & " cycles. New SSP offset value:" &
+                  integer'image(to_integer(unsigned(ssp_offset_corrected))));
+        else
+            ssp_offset_corrected := ssp_offset_generated;
+        end if;
+
+    end procedure;
+
     procedure ssp_cfg_feature_exec(
         signal      so              : out    feature_signal_outputs_t;
         signal      rand_ctr        : inout  natural range 0 to RAND_POOL_SIZE;
@@ -132,7 +170,8 @@ package body ssp_cfg_feature is
         variable num_bit_waits      :     natural;
         variable num_bit_waits_max  :     natural;
         variable tx_val             :     std_logic;
-
+        variable bit_rate           :     real;
+        variable cycles_per_bit     :     integer;
     begin
 
         -----------------------------------------------------------------------
@@ -151,12 +190,44 @@ package body ssp_cfg_feature is
         bus_timing.tq_nbt := 4;
         bus_timing.sjw_nbt := 5;
 
-        -- Should be 2 Mbit/s
-        bus_timing.prop_dbt := 10;
-        bus_timing.ph1_dbt := 20;
-        bus_timing.ph2_dbt := 19;
-        bus_timing.tq_dbt := 1;
-        bus_timing.sjw_dbt := 5;
+        -- Generate random data bit timing!
+        rand_int_v(rand_ctr, 63, bus_timing.prop_dbt);
+        rand_int_v(rand_ctr, 31, bus_timing.ph1_dbt);
+        rand_int_v(rand_ctr, 31, bus_timing.ph2_dbt);
+        
+        -- Constrain time quanta to something realistinc for data phase so
+        -- that we don't have too long run times!
+        rand_int_v(rand_ctr, 4, bus_timing.tq_dbt);
+        rand_int_v(rand_ctr, 33, bus_timing.sjw_dbt);
+        
+        -- Minimal time quanta
+        if (bus_timing.tq_dbt = 0) then
+            bus_timing.tq_dbt := 1;
+        end if;
+        
+        cycles_per_bit := bus_timing.tq_dbt * (1 + bus_timing.prop_dbt +
+                            bus_timing.ph1_dbt + bus_timing.ph2_dbt);
+        
+        -- Constrain minimal bit times
+        if (cycles_per_bit < 7) then
+            bus_timing.prop_dbt := 7;
+        end if;
+
+        if (bus_timing.tq_dbt = 1 and bus_timing.ph2_dbt = 1) then
+            bus_timing.ph2_dbt := 2;
+        end if;
+        
+        cycles_per_bit := bus_timing.tq_dbt * (1 + bus_timing.prop_dbt +
+                            bus_timing.ph1_dbt + bus_timing.ph2_dbt);
+        info("Cycles per bit:" & integer'image(cycles_per_bit));
+
+        info ("Generated data bit time bit-rate:");
+        info ("TQ: " & integer'image(bus_timing.tq_dbt));
+        info ("PROP: " & integer'image(bus_timing.prop_dbt));
+        info ("PH1: " & integer'image(bus_timing.ph1_dbt));
+        info ("PH2: " & integer'image(bus_timing.ph2_dbt));
+        bit_rate := 100000000.0 / (real(cycles_per_bit));
+        info ("Data bit rate: " & real'image(bit_rate/1000000.0) & " Mbit/s");
 
         -- We configure Nominal bit-rate to 500 Kbit/s so that generated
         -- TRV_DELAY will not cause error frames in arbitration bit-rate!
@@ -202,9 +273,12 @@ package body ssp_cfg_feature is
             info("TRV_DELAY + Offset");
             ssp_source := ssp_meas_n_offset;
             rand_logic_vect_v (rand_ctr, ssp_offset_var, 0.3);
+            info("Generated SSP offset: " & integer'image(to_integer(unsigned(ssp_offset_var))));
+            
+            correct_ssp_offset(ssp_offset_var, bus_timing, ssp_offset_var);
             
             -- SSP position is offset + delay
-            info("SSP offset: " & integer'image(to_integer(unsigned(ssp_offset_var))));
+            info("Post correction SSP offset: " & integer'image(to_integer(unsigned(ssp_offset_var))));
             info("Trv delay div: " & integer'image(rand_trv_delay / 10));
             
             ssp_pos := to_integer(unsigned(ssp_offset_var)) + rand_trv_delay / 10;
@@ -238,6 +312,10 @@ package body ssp_cfg_feature is
             ssp_source := ssp_offset;
             rand_logic_vect_v (rand_ctr, ssp_offset_var, 0.3);
             
+            correct_ssp_offset(ssp_offset_var, bus_timing, ssp_offset_var);
+            
+            info("Post correction SSP offset: " & integer'image(to_integer(unsigned(ssp_offset_var))));
+
             -- Here lengthen the SSP offset so that we are sufficiently over TRV_DELAY!
             -- It should be enough to lengthen it by two clock cycles (input delay of
             -- CTU CAN FD) + one cycle reserve for truncation of non-multiple of 10
@@ -282,6 +360,7 @@ package body ssp_cfg_feature is
 
         CAN_send_frame(frame_1, 1, ID_1, mem_bus(1), frame_sent);
         CAN_wait_pc_state(pc_deb_control, ID_1, mem_bus(1));
+        
         CAN_wait_not_pc_state(pc_deb_control, ID_1, mem_bus(1));
 
         -- +10 is to cover some part of CRC