framebuffer: saturate instead of overflow

diff --git a/milkymist/framebuffer/__init__.py b/milkymist/framebuffer/__init__.py
index d8f0cddd22e44599a08c852c7be51d732064409d..4161d6fbc2718de115eb7a91e95c820decdc559f 100644 (file)
--- a/milkymist/framebuffer/__init__.py
+++ b/milkymist/framebuffer/__init__.py
@@ -75,10 +75,14 @@ class Blender(PipelinedActor, AutoCSR):
                        for component in ["r", "g", "b"]:
                                incomps = [getattr(pix, component) for pix in inpixs]
                                outcomp = getattr(outpix, component)
-                               outcomp_full = Signal(18)
+                               outcomp_full = Signal(19)
                                self.comb += [
                                        outcomp_full.eq(sum(incomp*factor for incomp, factor in zip(incomps, factors))),
-                                       outcomp.eq(outcomp_full[8:])
+                                       If(outcomp_full[18],
+                                               outcomp.eq(2**10 - 1) # saturate on overflow
+                                       ).Else(
+                                               outcomp.eq(outcomp_full[8:18])
+                                       )
                                ]
 
                pipe_stmts = []
@@ -90,7 +94,7 @@ class Blender(PipelinedActor, AutoCSR):
                self.comb += self.source.payload.eq(outval)
 
 class MixFramebuffer(Module, AutoCSR):
-       def __init__(self, pads, *asmiports, blender_latency=4):
+       def __init__(self, pads, *asmiports, blender_latency=5):
                pack_factor = asmiports[0].hub.dw//(2*bpp)
                packed_pixels = structuring.pack_layout(pixel_layout, pack_factor)