Fix the sync polarity (negative)

mole99 · Apr 19, 2024 · 71e936f · 71e936f
1 parent 6b80879
commit 71e936f
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Showing 3 changed files with 43 additions and 14 deletions.
diff --git a/src/timing.sv b/src/timing.sv
@@ -23,8 +23,13 @@ module timing #(
 
     // Signal to trigger next counter in the chain
     assign next = counter >= RESOLUTION - 1 && enable;
-    assign sync  = POLARITY ? (counter >= -SYNC_PULSE - BACK_PORCH) && (counter < -BACK_PORCH) :
-                             ~(counter >= -SYNC_PULSE - BACK_PORCH) && (counter < -BACK_PORCH);
+
+    // Create the sync signal
+    logic sync_tmp;
+    assign sync_tmp = (counter >= -SYNC_PULSE - BACK_PORCH) && (counter < -BACK_PORCH);
+    assign sync = POLARITY ? sync_tmp : ~sync_tmp;
+
+    // Blanking
     assign blank = (counter >= -FRONT_PORCH - SYNC_PULSE - BACK_PORCH) && (counter < 0);
 
     // Counter logic

diff --git a/src/tiny_shader_top.sv b/src/tiny_shader_top.sv
@@ -68,7 +68,7 @@ module tiny_shader_top (
         .SYNC_PULSE     (HSYNC),
         .BACK_PORCH     (HBACK),
         .TOTAL          (HTOTAL),
-        .POLARITY       (1)
+        .POLARITY       (1'b0)
     ) timing_hor (
         .clk        (clk_i),
         .enable     (1'b1),
@@ -87,7 +87,7 @@ module tiny_shader_top (
         .SYNC_PULSE     (VSYNC),
         .BACK_PORCH     (VBACK),
         .TOTAL          (VTOTAL),
-        .POLARITY       (1)
+        .POLARITY       (1'b0)
     ) timing_ver (
         .clk        (clk_i),
         .enable     (next_vertical),

diff --git a/test/test.py b/test/test.py
@@ -27,13 +27,23 @@
 VSYNC    = 2
 VBACK    = 33
 
+POLARITY = 0
+
 # Reset coroutine
 async def reset_dut(rst_ni, duration_ns):
     rst_ni.value = 0
     await Timer(duration_ns, units="ns")
     rst_ni.value = 1
     rst_ni._log.debug("Reset complete")
 
+async def sync_frame(dut):
+    if POLARITY:
+        await FallingEdge(dut.vsync)
+        await FallingEdge(dut.hsync)
+    else:
+        await RisingEdge(dut.vsync)
+        await RisingEdge(dut.hsync)
+
 # Draw the current frame and return it
 async def draw_frame(dut):
     screen_x = -HBACK
@@ -67,25 +77,33 @@ async def draw_frame(dut):
             pixels[screen_x, screen_y] = (r, g, b)
 
         # Received hsync
-        if (dut.hsync.value == 1):
-            await FallingEdge(dut.hsync)
+        if (dut.hsync.value == POLARITY):
+            if POLARITY:
+                await FallingEdge(dut.hsync)
+            else:
+                await RisingEdge(dut.hsync)
+
             screen_y += 1
             #print(dut.timing_hor.counter.value.integer)
             #print(dut.timing_ver.counter.value.integer)
             print(f"line {screen_y}")
             screen_x = -HBACK
 
         # Received vsync
-        elif (dut.vsync.value == 1):
-            await FallingEdge(dut.vsync)
-            await FallingEdge(dut.hsync)
+        elif (dut.vsync.value == POLARITY):
+            if POLARITY:
+                await FallingEdge(dut.vsync)
+                await FallingEdge(dut.hsync)
+            else:
+                await RisingEdge(dut.vsync)
+                await RisingEdge(dut.hsync)
             return image
         else:
             screen_x += 1
 
 @cocotb.test()
 async def test_vga_default(dut):
-    """Draw one frame with the default shader"""
+    """Draw two frames with the default shader"""
 
     # Start the clock
     c = Clock(dut.clk, 10, 'ns')
@@ -99,14 +117,20 @@ async def test_vga_default(dut):
     await reset_dut(dut.rst_n, 50)
     dut._log.info("Reset done")
 
-    await FallingEdge(dut.vsync)
-    await FallingEdge(dut.hsync)
+    # Sync to start of frame
+    await sync_frame(dut)
 
     # Start thread to draw frame
     task_draw_frame = await cocotb.start(draw_frame(dut))
 
     image = await task_draw_frame.join()
     image.save(f"default.png")
+
+    # Start thread to draw frame
+    task_draw_frame = await cocotb.start(draw_frame(dut))
+
+    image = await task_draw_frame.join()
+    image.save(f"default2.png")
 
     await ClockCycles(dut.clk, 10)
 
@@ -165,8 +189,8 @@ async def test_vga_load(dut, shader_name='test7'):
     # Send new shader instructions
     await spi_master.write(shader, burst=True)
 
-    await FallingEdge(dut.vsync)
-    await FallingEdge(dut.hsync)
+    # Sync to start of frame
+    await sync_frame(dut)
 
     # Start thread to draw frame
     task_draw_frame = await cocotb.start(draw_frame(dut))