gw: finish testing sampler and fix a couple bugs

gateware/sampler.py

@@ -62,13 +62,13 @@ class CircularBuffer(Module):
                 empty.eq(0),
 
                 # Advance write pointer
-                If(wr_ptr < depth,
+                If(wr_ptr < (depth - 1),
                    wr_ptr.eq(wr_ptr + 1))
                 .Else(wr_ptr.eq(0)),
 
                 # Advance read pointer if we are full (e.g. overwrite old data)
-                If(~empty & wr_ptr == rd_ptr,
-                    If(rd_ptr < depth,
+                If(~empty & (wr_ptr == rd_ptr),
+                    If(rd_ptr < (depth - 1),
                        rd_ptr.eq(rd_ptr + 1))
                     .Else(rd_ptr.eq(0))
                 )
@@ -91,7 +91,7 @@ class CircularBuffer(Module):
         self.comb += [
             If(empty, self.len.eq(0))
             .Else(
-                If(wr_ptr >= rd_ptr,
+                If(wr_ptr > rd_ptr,
                     self.len.eq(wr_ptr - rd_ptr))
                 .Elif(wr_ptr != rd_ptr,
                     self.len.eq(depth - (rd_ptr - wr_ptr)))
@@ -106,7 +106,7 @@ class CircularBuffer(Module):
         # Technically there's some glitches that can happen here if we write data while clear
         # is asserted, but that shouldn't happen and it's fine if it does tbh.
         self.sync += If(self.clear,
-                        wr_ptr.eq(0), rd_ptr.eq(0), empty.eq(0))
+                        wr_ptr.eq(0), rd_ptr.eq(0), empty.eq(1))
 
 
 class Sampler(Module):
@@ -146,16 +146,19 @@ def fifo_testbench():
             (yield dut.wr_valid.eq(1))
             yield
 
-        fifo_len = (yield dut.len)
-        assert fifo_len == 4, f"len should be 4, is {fifo_len}"
-
         # Stop clocking data in
         (yield dut.wr_valid.eq(0))
+        # Tick again because setting a value waits until the next clock...
+        yield
+
+        fifo_len = (yield dut.len)
+        assert fifo_len == 4, f"len should be 4, is {fifo_len}"
 
         # Reset
         (yield dut.clear.eq(1))
         yield
-        (yield dut.cleart.eq(0))
+        (yield dut.clear.eq(0))
+        yield
 
         # Len should be cleared
         assert (yield dut.len) == 0
@@ -168,16 +171,22 @@ def fifo_testbench():
             (yield dut.wr_valid.eq(1))
             yield
 
+        # One more clock
+        (yield dut.wr_valid.eq(0))
+        yield
+
         data_len = (yield dut.len)
-        assert data_len == 24
+        assert data_len == 24, f"len should be 24, is {data_len}"
         out_data = []
         for i in range(24):
             (yield dut.rd_addr.eq(i))
+            yield
+
             out_data.append((yield dut.rd_data))
 
-            assert out_data[i] == data[i + 8], f"Data mismatch at index {i}"
+            assert out_data[i] == data[i + 8], f"Data mismatch at index {i}, should be {data[i+8]}, is {out_data[i]}"
 
-        # At this point, seems to be working
+        # At this point, everything seems to be good, so I'm leaving more exhaustive testing
 
     run_simulation(dut, test_fn())