generic/examples: Add FASM writer Python script

Signed-off-by: David Shah <dave@ds0.me>

generic/examples/write_fasm.py

@@ -0,0 +1,52 @@
+from collections import namedtuple
+
+"""
+	write:   set to True to enable writing this parameter to FASM
+
+	numeric: set to True to write this parameter as a bit array (width>1) or
+	         single bit (width==1) named after the parameter. Otherwise this
+	         parameter will be written as `name.value`
+
+	width:   width of numeric parameter (ignored for non-numeric parameters)
+	
+	alias:   an alternative name for this parameter (parameter name used if alias
+	         is None)
+"""
+ParameterConfig = namedtuple('ParameterConfig', 'write numeric width alias')
+
+# FIXME use defaults= once Python 3.7 is standard
+ParameterConfig.__new__.__defaults__ = (False, True, 1, None)
+
+
+"""
+Write a design as FASM
+
+    ctx:      nextpnr context
+    paramCfg: ParameterConfig describing how to write parameters
+    f:        output file
+"""
+def write_fasm(ctx, paramCfg, f):
+	for nname, net in sorted(ctx.nets, key=lambda x: str(x[1].name)):
+		print("# Net %s" % nname, file=f)
+		for wire, pip in sorted(net.wires, key=lambda x: str(x[1])):
+			if pip.pip != "":
+				print("%s" % pip.pip, file=f)
+		print("", file=f)
+	for cname, cell in sorted(ctx.cells, key=lambda x: str(x[1].name)):
+		print("# Cell %s at %s" % (cname, cell.bel), file=f)
+		for param, val in sorted(cell.params, key=lambda x: str(x)):
+			cfg = paramCfg[(cell.type, param)]
+			if not cfg.write:
+				continue
+			fasm_name = cfg.alias if cfg.alias is not None else param
+			if cfg.numeric:
+				if cfg.width == 1:
+					if int(val) != 0:
+						print("%s.%s" % (cell.bel, fasm_name), file=f)
+				else:
+					# Parameters with width >32 are direct binary, otherwise denary
+					binval = val if cfg.width > 32 else "{:0{}b}".format(int(val), cfg.width)
+					print("%s.%s[%d:0] = %d'b%s" % (cell.bel, fasm_name, cfg.width-1, cfg.width, binval), file=f)
+			else:
+				print("%s.%s.%s" % (cell.bel, fasm_name, val), file=f)
+		print("", file=f)