src/soc/experiment/imem.py

   1 from soc.minerva.units.fetch import FetchUnitInterface
   2 from nmigen import Signal, Module, Elaboratable, Mux
   3 from soc.experiment.testmem import TestMemory
   4 from nmigen.cli import rtlil
   5
   6
   7 class TestMemFetchUnit(FetchUnitInterface, Elaboratable):
   8
   9     def __init__(self, addr_wid=32, data_wid=32):
  10         super().__init__(addr_wid=addr_wid, data_wid=data_wid)
  11         # limit TestMemory to 2^6 entries of regwid size
  12         self.mem = TestMemory(self.data_wid, 6, readonly=True)
  13
  14     def elaborate(self, platform):
  15         m = Module()
  16         regwid, addrwid = self.data_wid, self.addr_wid
  17         adr_lsb = self.adr_lsbs
  18
  19         m.submodules.mem = mem = self.mem
  20
  21         do_fetch = Signal()  # set when fetch while valid and not stalled
  22         m.d.comb += do_fetch.eq(self.a_valid_i & ~self.a_stall_i)
  23
  24         # bit of a messy FSM that progresses from idle to in progress
  25         # to done.
  26         op_actioned = Signal(reset=0)
  27         op_in_progress = Signal(reset=0)
  28         with m.If(~op_actioned & do_fetch): # idle
  29             m.d.sync += op_actioned.eq(1)
  30             m.d.sync += op_in_progress.eq(1)
  31         with m.Elif(op_in_progress):                    # in progress
  32             m.d.sync += op_actioned.eq(0)
  33         with m.If(~do_fetch):               # done
  34             m.d.sync += op_in_progress.eq(0)
  35
  36         m.d.comb += self.a_busy_o.eq(op_actioned & self.a_valid_i)
  37         # fetch
  38         m.d.comb += mem.rdport.addr.eq(self.a_pc_i[adr_lsb:])
  39         m.d.comb += self.f_instr_o.eq(mem.rdport.data)
  40
  41         return m
  42
  43
  44 if __name__ == '__main__':
  45     dut = TestMemFetchUnit(addr_wid=32, data_wid=32)
  46     vl = rtlil.convert(dut, ports=[]) # TODOdut.ports())
  47     with open("test_imem.il", "w") as f:
  48         f.write(vl)
  49