From cb06c203a8e9f57d0ff61bf55007946b4eb542ef Mon Sep 17 00:00:00 2001
From: jjsuperpower <jjs29356@gmail.com>
Date: Mon, 5 Sep 2022 20:10:16 -0500
Subject: honestly i don't know what I did

---
 hdl/core/reg.py | 304 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 304 insertions(+)
 create mode 100644 hdl/core/reg.py

(limited to 'hdl/core')

diff --git a/hdl/core/reg.py b/hdl/core/reg.py
new file mode 100644
index 0000000..b6aa3c5
--- /dev/null
+++ b/hdl/core/reg.py
@@ -0,0 +1,304 @@
+from amaranth import *
+from amaranth.sim import Settle
+
+from hdl.lib.in_out_buff import InOutBuff
+from hdl.utils import cmd, step, sim
+
+class Reg(Elaboratable):
+    def __init__(self, **kargs):  # sim is only for modularity, does nothing for this
+
+        ################ INPUTS ################
+        self.wr_en = Signal(1)
+        self.stall = Signal(1)  # stall instruction pointer increment
+
+        self.rd = Signal(32)
+        self.rd_addr = Signal(4)
+        self.rs1_addr = Signal(4)
+        self.rs2_addr = Signal(4)
+
+        self.alu_flgs = Signal(5)   # flags from alu
+
+        # these signals should be used one hot only
+        self.int_sig = Signal(1)    # unconditional interrupt
+        self.iret = Signal(1)       # return from interrupt
+        self.call = Signal(1)       # call subroutine, save return address
+        self.jump = Signal(1)       # jump, do not save return address
+
+
+        ################ OUTPUTS ################
+
+        self.rs1 = Signal(32)   # read data 1
+        self.rs2 = Signal(32)   # read data 2
+
+        self.int_en = Signal(1)     #interupt enable output signal to control unit
+        self.user_mode = Signal(1)  # user mode output signal to control unit
+
+
+        ################ INTERNAL SIGNALS ################
+        self._wr_alu_flg = Signal(1)
+        self._inc_ip = Signal(1)
+
+        self.zx = Signal(32)    #0
+        self.ax = Signal(32)    #1
+        self.bx = Signal(32)    #2
+        self.bx = Signal(32)    #3
+        self.cx = Signal(32)    #4
+        self.dx = Signal(32)    #5
+        self.ex = Signal(32)    #6
+        self.fx = Signal(32)    #7
+        self.gx = Signal(32)    #8
+        self.hx = Signal(32)    #9
+        self.ip = Signal(32)    #10
+        self.sp = Signal(32)    #11
+        self.flg = Signal(32)   #12
+        self.cs0 = Signal(32)   #13
+        self.cs1 = Signal(32)   #14
+        self.cs2 = Signal(32)   #15
+        self.pda = Signal(32)   #16
+
+        # for sake of modularity, make bit locations easily configurable
+        setattr(self.flg, 'c', self.flg[0])
+        setattr(self.flg, 'ov', self.flg[1])
+        setattr(self.flg, 'z', self.flg[2])
+        setattr(self.flg, 'n', self.flg[3])
+        setattr(self.flg, 'od', self.flg[4])
+        setattr(self.flg, 'int', self.flg[16])
+        setattr(self.flg, 'user_mode', self.flg[17])
+        setattr(self.flg, 'page_en', self.flg[18])
+
+
+        reg_list = [self.zx, self.ax, self.bx, self.cx, self.dx, self.ex, self.fx, self.gx, self.hx, self.ip, self.sp, self.flg, self.cs0, self.cs1, self.cs2, self.pda]
+        for idx, reg in enumerate(reg_list):
+            setattr(reg, 'idx', idx)        # set idx attribute to each register
+
+        self.reg_arr = Array(reg_list)
+
+        ports_in = [self.wr_en, self.alu_flgs, self.int_sig, self.iret, self.call, self.jump, self.rd_addr, self.rd, self.rs1_addr, self.rs2_addr]
+        ports_out = [self.int_en, self.user_mode, self.rs1, self.rs2, self.ip]
+        self.ports = {'in': ports_in, 'out': ports_out}
+
+
+    def elaborate(self, platform=None):
+        m = Module()
+
+        # output signals to control unit
+        m.d.comb += self.int_en.eq(self.flg.int)
+        m.d.comb += self.user_mode.eq(self.flg.user_mode & ~self.int_sig)
+
+        # defualt value of internal signals
+        m.d.comb += self._wr_alu_flg.eq(1)
+        m.d.comb += self._inc_ip.eq(1)
+
+        with m.If(self.int_sig):
+            m.d.comb += self._inc_ip.eq(0)
+            m.d.sync += self.ip.eq(self.rd)
+            m.d.sync += self.cs0.eq(self.ip)
+            m.d.sync += self.cs1.eq(self.sp)
+            m.d.sync += self.cs2.eq(self.flg)
+            m.d.sync += self.flg.user_mode.eq(0)    # set to system mode or iret cannot be used
+            m.d.sync += self.flg.int.eq(0)          # clear int flag, essential because another interrupt can be triggered without this
+
+        with m.Elif(self.iret):
+            m.d.comb += self._inc_ip.eq(0)
+            m.d.sync += self.ip.eq(self.cs0)
+            m.d.sync += self.sp.eq(self.cs1)
+            m.d.sync += self.flg.eq(self.cs2)
+
+        with m.Elif(self.call):
+            m.d.comb += self._inc_ip.eq(0)
+            m.d.sync += self.ip.eq(self.rd)
+            m.d.sync += self.cs0.eq(self.ip)
+
+        with m.Elif(self.jump):
+            m.d.comb += self._inc_ip.eq(0)
+            m.d.sync += self.ip.eq(self.cs0)
+
+        with m.Elif(self.wr_en):
+            with m.Switch(self.rd_addr):
+                with m.Case(self.zx.idx):    # do not write to zero register
+                    pass
+
+                with m.Case(self.ip.idx):    #do not directly write to ip register
+                    pass
+
+                with m.Case(self.flg.idx):
+                    # mask top half of register to prevent writing to flags in user mode
+                    with m.If(~self.flg.user_mode):
+                        m.d.sync += self.flg.eq(self.rd)    # system mode, full control
+                    with m.Else():
+                        m.d.sync += self.flg.eq(Cat(self.rd[:16], self.flg[16:]))   # usermode can only effect lower 16 bits
+
+                    # don't update flags from alu
+                    m.d.comb += self._wr_alu_flg.eq(0)
+
+                with m.Case():
+                    m.d.sync += self.reg_arr[self.rd_addr].eq(self.rd)
+
+            with m.If(self._wr_alu_flg):    # alu flags are written only if write enabled and not writing to flags register
+                m.d.sync += self.flg.eq(Cat(self.alu_flgs, self.flg[len(self.alu_flgs):]))
+
+
+        with m.If(self._inc_ip & ~self.stall):            # increment ip if not directly writing to ip register
+            m.d.sync += self.ip.eq(self.ip + 4)
+
+        
+        ### Combination signal outputs ###
+        with m.Switch(self.rs1_addr):
+            with m.Case(self.flg.idx):
+                m.d.comb += self.rs1.eq(self.flg & Cat(Const(0xFFFF, 16), Repl(~self.flg.user_mode, 16)))
+            with m.Case():
+                m.d.comb += self.rs1.eq(self.reg_arr[self.rs1_addr])
+
+        with m.Switch(self.rs2_addr):
+            with m.Case(self.flg.idx):
+                m.d.comb += self.rs2.eq(self.flg & Cat(Const(0xFFFF, 16), Repl(~self.flg.user_mode, 16)))
+            with m.Case():
+                m.d.comb += self.rs2.eq(self.reg_arr[self.rs2_addr])
+        
+        return m
+
+
+#--------------------------------- TEST BENCH BELOW ---------------------------------#
+
+def _init(dut):
+    for i in range(16):
+        yield dut.reg_arr[i].eq(i)
+        yield Settle()
+
+
+# test combinational output
+def test_reg_comb_output():
+    dut = Reg()
+    def proc():
+        yield from _init(dut)
+        for i in range(16):
+            yield dut.rs1_addr.eq(i)
+            yield Settle()
+            assert (yield dut.rs1) == i, f'ERROR reading {dut.reg_arr[i].name} != {i}'
+        for i in range(16):
+            yield dut.rs2_addr.eq(i)
+            yield Settle()
+            assert (yield dut.rs2) == i, f'ERROR reading {dut.reg_arr[i].name} != {i}'
+    sim(dut, proc)
+
+# test writeback with writeback disabled
+def test_reg_writeback_dsb():
+    dut = Reg()
+    def proc():
+        yield from _init(dut)
+        for i in range(16):
+            yield dut.rd_addr.eq(i)
+            yield dut.rd.eq(i + 1)
+            yield from step()
+            if (i != dut.ip.idx) and (i != dut.flg.idx):     # flag gets update by the alu
+                assert (yield dut.reg_arr[i]) == i, f'ERROR writing to {dut.reg_arr[i].name} != {i}'
+    sim(dut, proc)
+        
+# test writeback with writeback enabled
+def test_reg_writeback_en():
+    dut = Reg()
+    def proc():
+        for i in range(16):
+            yield from _init(dut)
+            yield dut.wr_en.eq(1)
+            yield dut.rd_addr.eq(i)
+            yield dut.rd.eq(i - 1)
+            yield from step()
+            if (i != dut.zx.idx) and (i != dut.ip.idx):
+                assert (yield dut.reg_arr[i]) == i-1, f'ERROR writing to {dut.reg_arr[i].name} != {i-1}'
+            elif i == dut.zx.idx:
+                assert (yield dut.zx) == 0, f'ERROR {dut.zx.name} != 0'
+            elif i == dut.ip.idx:
+                # ip should be incremented and not written to
+                assert (yield dut.reg_arr[i]) == i+1, f'ERROR {dut.ip.name} != {i + 1} should not be able to be directly written to'
+    sim(dut, proc)
+
+# check to make sure alu is writing values
+def test_reg_flg_write_aluflg():
+    dut = Reg()
+    def proc():
+        yield dut.flg.eq(0)
+        yield dut.alu_flgs.eq(Repl(1, dut.alu_flgs.width))
+        yield dut.wr_en.eq(1)
+        yield dut.flg.user_mode.eq(0)
+        yield dut.rd_addr.eq(dut.zx.idx)    # can be anything except flg register
+        yield dut.rd.eq(0xFFFF0000)         # this does not matter
+        yield from step()
+        assert (yield dut.flg) == (yield dut.alu_flgs), f'ERROR: alu is not writing to flg register'
+    sim(dut, proc)
+
+def test_reg_flg_overwrite():
+    dut = Reg()
+    def proc():
+        yield dut.flg.eq(0)
+        yield dut.alu_flgs.eq(Repl(1, dut.alu_flgs.width))
+        yield dut.wr_en.eq(1)
+        yield dut.flg.user_mode.eq(0)
+        yield dut.flg[15].eq(1)
+        yield dut.flg[31].eq(1)
+        yield dut.rd_addr.eq(dut.flg.idx)
+        yield dut.rd.eq(0xFFFF0000)
+        yield from step()
+        assert (yield dut.flg) == (0xFFFF0000), f'ERROR: alu status should not be to flag'
+    sim(dut, proc)
+
+# test flag register security
+def test_reg_flg_read_usermode():
+    dut = Reg()
+    def proc():
+        yield dut.flg.eq(0)
+        yield dut.flg.user_mode.eq(1)
+        yield dut.flg[15].eq(1)
+        yield dut.flg[31].eq(1)
+        yield dut.rs1_addr.eq(dut.flg.idx)
+        yield Settle()
+        assert (yield dut.rs1) == 0x00008000, f'ERROR: able to read upper 16 bits of flg reg in user mode'
+    sim(dut, proc)
+
+# test flag register security
+def test_reg_flg_write_usermode():
+    dut = Reg()
+    def proc():
+        yield dut.flg.eq(0)
+        yield dut.wr_en.eq(1)
+        yield dut.flg.user_mode.eq(1)
+        yield dut.flg[15].eq(1)
+        yield dut.flg[31].eq(1)
+        yield dut.rd_addr.eq(dut.flg.idx)
+        yield dut.rd.eq(0xABCD5789)
+        yield from step()
+        assert (yield dut.flg) == (0x80020000 | 0x5789), f'ERROR: able to write to upper 16 bits of flg reg in user mode'
+    sim(dut, proc)
+
+def test_reg_flg_read_systemmode():
+    dut = Reg()
+    def proc():
+        yield dut.flg.eq(0)
+        yield dut.flg.user_mode.eq(0)
+        yield dut.flg[15].eq(1)
+        yield dut.flg[31].eq(1)
+        yield dut.rs1_addr.eq(dut.flg.idx)
+        yield Settle()
+        assert (yield dut.rs1) == 0x80008000, f'ERROR: able to read all bits of flg reg in system mode'
+    sim(dut, proc)
+
+# make sure not to write alu flags when directly writing to flg register
+def test_reg_flg_write_systemmode():
+    dut = Reg()
+    def proc():
+        yield dut.flg.eq(0)
+        yield dut.wr_en.eq(1)
+        yield dut.flg.user_mode.eq(0)
+        yield dut.flg[15].eq(1)
+        yield dut.flg[31].eq(1)
+        yield dut.rd_addr.eq(dut.flg.idx)
+        yield dut.rd.eq(0xABCD5789)
+        yield from step()
+        assert (yield dut.flg) == (0xABCD5789), f'ERROR: unamble to write to all bits in supervisor mode'
+    sim(dut, proc)
+
+
+
+if __name__ == '__main__':
+    reg = InOutBuff(Reg())
+    cmd(reg)
\ No newline at end of file
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