counter: add register to set counter value

- Setting the counter takes precedence over a trigger event, that way the
block will output the set value at least for one tick
- It is possible to set a value while the block is disabled (this allows to
control the pos bus value without having to actually count)
- Timing tests were added for two cases: setting a value while enabled and
setting a value while disabled
- Python counter simulation script was updated to consider the set register

modules/counter/counter.block.ini

@@ -28,6 +28,11 @@ description: Counter OUT update mode (on internal counter value change or on ENA
 0: On-Change
 1: On-Disable
 
+[SET]
+type: param int
+description: set current value of a counter
+wstb: true
+
 [START]
 type: param int
 description: Counter start value

modules/counter/counter.timing.ini

@@ -202,4 +202,15 @@ scope: counter.block.ini
 10      : TRIG=0            -> CARRY=0
 11      : TRIG=1            -> OUT=-3
 12      : TRIG=0
-13      : ENABLE=0
+13      : ENABLE=0
+
+[Manual set value]
+3       : START=20
+6       : ENABLE=1           -> OUT=20
+9       : TRIG=1             -> OUT=21
+10      : SET=10, TRIG=0     -> OUT=10
+11      : TRIG=1             -> OUT=11
+12      : TRIG=0, ENABLE=0
+
+[Manual set value disabled]
+3       : SET=42             -> OUT=42

modules/counter/counter_sim.py

@@ -16,7 +16,7 @@
 
 
 class CounterSimulation(BlockSimulation):
-    ENABLE, TRIG, DIR, TRIG_EDGE, OUT_MODE, START, STEP, MAX, MIN, CARRY, OUT = PROPERTIES
+    ENABLE, TRIG, DIR, TRIG_EDGE, OUT_MODE, SET, START, STEP, MAX, MIN, CARRY, OUT = PROPERTIES
 
     def __init__(self):
         self.counter = 0
@@ -50,6 +50,8 @@ def on_changes(self, ts, changes):
         if self.OUT_MODE == MODE_OnChange:
             if changes.get(NAMES.ENABLE, None) is 1:
                 self.OUT = self.START
+            elif NAMES.SET in changes:
+                self.OUT = self.SET
             elif changes.get(NAMES.ENABLE, None) is 0:
                 self.CARRY = 0
             elif self.ENABLE and NAMES.TRIG in changes:
@@ -75,6 +77,8 @@ def on_changes(self, ts, changes):
             if changes.get(NAMES.ENABLE, None) is 1:
                 self.counter = self.START
                 self.overflow = 0
+            elif NAMES.SET in changes:
+                self.counter = self.SET
             elif self.ENABLE and NAMES.TRIG in changes:
                 # process trigger on selected edge
                 if got_trigger:
@@ -93,4 +97,4 @@ def on_changes(self, ts, changes):
                         self.overflow = 1
             elif changes.get(NAMES.ENABLE, None) is 0:
                 self.OUT = self.counter
-                self.CARRY = self.overflow
+                self.CARRY = self.overflow

modules/counter/hdl/counter.vhd

@@ -28,6 +28,8 @@ port (
     TRIG_EDGE           : in  std_logic_vector(31 downto 0) := (others => '0');
     TRIG_EDGE_WSTB      : in  std_logic;
     OUT_MODE            : in  std_logic_vector(31 downto 0);
+    SET                 : in  std_logic_vector(31 downto 0);
+    SET_WSTB            : in  std_logic;
     START               : in  std_logic_vector(31 downto 0);
     START_WSTB          : in  std_logic;
     STEP                : in  std_logic_vector(31 downto 0);
@@ -130,6 +132,9 @@ begin
         if (enable_rise = '1') then
             counter <= signed(START);
             carry_latch <= '0';
+        elsif (SET_WSTB = '1') then
+            counter <= signed(SET);
+            carry_latch <= '0';
         -- Drop the carry signal on falling enable
         elsif (enable_fall = '1') then
             counter_carry <= '0';