src/soc/experiment/cache_ram.py

   1 # TODO: replace with Memory at some point
   2 from nmigen import Elaboratable, Signal, Array, Module
   3
   4 class CacheRam(Elaboratable):
   5
   6     def __init__(self, ROW_BITS=16, WIDTH = 64, TRACE=False, ADD_BUF=False):
   7         self.ROW_BITS = ROW_BITS
   8         self.WIDTH = WIDTH
   9         self.TRACE = TRACE
  10         self.ADD_BUF = ADD_BUF
  11         self.rd_en     = Signal()
  12         self.rd_addr   = Signal(ROW_BITS)
  13         self.rd_data_o = Signal(WIDTH)
  14         self.wr_sel    = Signal(WIDTH//8)
  15         self.wr_addr   = Signal(ROW_BITS)
  16         self.wr_data   = Signal(WIDTH)
  17
  18     def elaborate(self, platform):
  19         m = Module()
  20         comb, sync = m.d.comb, m.d.sync
  21
  22         ROW_BITS = self.ROW_BITS
  23         WIDTH = self.WIDTH
  24         TRACE = self.TRACE
  25         ADD_BUF = self.ADD_BUF
  26         SIZE = 2**ROW_BITS
  27
  28         ram = Array(Signal(WIDTH) for i in range(SIZE))
  29         #attribute ram_style of ram : signal is "block";
  30
  31         rd_data0 = Signal(WIDTH)
  32
  33         sel0 = Signal(WIDTH//8) # defaults to zero
  34
  35         with m.If(TRACE):
  36             with m.If(self.wr_sel != sel0):
  37                 #Display( "write a:" & to_hstring(wr_addr) &
  38                 #    " sel:" & to_hstring(wr_sel) &
  39                 #    " dat:" & to_hstring(wr_data))
  40                pass
  41         for i in range(WIDTH//8):
  42             lbit = i * 8;
  43             mbit = lbit + 8;
  44             with m.If(self.wr_sel[i]):
  45                 sync += ram[self.wr_addr][lbit:mbit].eq(self.wr_data[lbit:mbit])
  46         with m.If(self.rd_en):
  47             if ADD_BUF:
  48                 sync += self.rd_data_o.eq(ram[self.rd_addr])
  49             else:
  50                 comb += self.rd_data_o.eq(ram[self.rd_addr])
  51
  52         if TRACE:
  53             # Display( "read a:" & to_hstring(rd_addr) &
  54             #" dat:" & to_hstring(ram(to_integer(unsigned(rd_addr))));
  55             pass
  56
  57         return m