Add sigma-delta DAC LiteX core.

Signed-off-by: Tim Callahan <tcal@google.com>

litex/soc/cores/dac.py

@@ -0,0 +1,24 @@
+#
+# This file is part of LiteX.
+#
+# Copyright (c) 2022 Tim Callahan <tcal@google.com>
+# SPDX-License-Identifier: BSD-2-Clause
+
+from migen import *
+
+from litex.soc.interconnect.csr import *
+
+# DAC  ---------------------------------------------------------------------------------------
+
+class DAC(Module, AutoCSR):
+
+    def __init__(self, out, data_width):
+        self.out    = out
+
+        self._value = CSRStorage(data_width, reset_less=True, description="Digital value to convert to analog.")
+        value       = Signal(data_width)
+        accum       = Signal(data_width+1)
+
+        self.comb   += value.eq(self._value.storage)
+        self.sync   += accum.eq(accum[0:data_width] + value)
+        self.comb   += out.eq(accum[data_width])