reorganise cpu regfile, to separate module, with 2R1W interface

[rv32.git] / regfile.py

diff --git a/regfile.py b/regfile.py
new file mode 100644 (file)
index 0000000..b544372
--- /dev/null
+++ b/regfile.py
@@ -0,0 +1,95 @@
+"""
+/*
+ * Copyright 2018 Jacob Lifshay
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+`timescale 1ns / 1ps
+`include "riscv.vh"
+`include "cpu.vh"
+"""
+
+from migen import *
+from migen.fhdl import verilog
+
+class RegFile(Module):
+
+    def __init__(self):
+        Module.__init__(self)
+        l = []
+        for i in range(31):
+            r = Signal(32, name="register%d" % i)
+            l.append(r)
+            self.sync += r.eq(Constant(0, 32))
+        self.registers = Array(l)
+
+        self.ra_en = Signal() # read porta enable
+        self.rb_en = Signal() # read portb enable
+        self.w_en = Signal()  # write enable
+        self.read_a = Signal(32) # result porta read
+        self.read_b = Signal(32) # result portb read
+        self.writeval = Signal(32) # value to write
+        self.rs_a = Signal(5) # register port a to read
+        self.rs_b = Signal(5) # register port b to read
+        self.rd = Signal(5) # register to write
+
+        self.sync += If(self.ra_en,
+                        self.read(self.rs_a, self.read_a)
+                     )
+        self.sync += If(self.rb_en,
+                        self.read(self.rs_b, self.read_b)
+                     )
+        self.sync += If(self.w_en,
+                        self.write_register(self.rd, self.writeval)
+                     )
+
+    def read(self, regnum, dest):
+        """ sets the destination register argument
+            regnum =  0, dest = 0
+            regnum != 0, dest = regs[regnum-1]
+        """
+        return If(regnum == Constant(0, 5),
+                   dest.eq(Constant(0, 32))
+               ).Else(
+                   dest.eq(self.registers[regnum-1])
+               )
+
+    def write_register(self, regnum, value):
+        """ writes to the register file if the regnum is not zero
+        """
+        return If(regnum != 0,
+                  self.registers[regnum].eq(value)
+               )
+
+if __name__ == "__main__":
+    example = RegFile()
+    print(verilog.convert(example,
+         {
+           example.ra_en,
+           example.rb_en,
+           example.w_en,
+           example.read_a,
+           example.read_b,
+           example.writeval,
+           example.rs_a,
+           example.rs_b,
+           example.rd,
+           }))
+