gary/vram/VRAM.bsv

package VRAM;

import GetPut::*;
import ClientServer::*;
import DReg::*;
import BRAM::*;
import Vector::*;
import FIFOF::*;
import SpecialFIFOs::*;

import DelayLine::*;
import ECP5_RAM::*;

typedef UInt#(17) VRAMAddr;

typedef Bit#(8) VRAMData;

// Each byte RAM we build below can address 4096 bytes, which is 12
// address bits.
typedef UInt#(12) ByteAddr;

// The difference between ByteRAM_Addr and VRAMAddr is the chip
// select ID.
typedef UInt#(5) ChipAddr;

// ByteRAM is two EBRs glued together to make a whole-byte memory.
typedef EBR#(ByteAddr, VRAMData, ByteAddr, VRAMData) ByteRAM;

// mkByteRAM glues two ECP5 EBRs together to make a 4096x8b memory
// block. Like the underlying ECP5 EBRs, callers must bring their own
// flow control to read out responses one cycle after putting a read
// request.
module mkByteRAM(UInt#(3) chip_addr, ByteRAM ifc);
   EBRPortConfig cfg = defaultValue;
   cfg.chip_select_addr = chip_addr;
   EBR#(ByteAddr, Bit#(4), ByteAddr, Bit#(4)) upper <- mkEBRCore(cfg, cfg);
   EBR#(ByteAddr, Bit#(4), ByteAddr, Bit#(4)) lower <- mkEBRCore(cfg, cfg);

   interface EBRPort portA;
      method Action put(UInt#(3) chip_select, Bool write, ByteAddr addr, VRAMData data_in);
         upper.portA.put(chip_select, write, addr, truncate(data_in>>4));
         lower.portA.put(chip_select, write, addr, truncate(data_in));
      endmethod

      method VRAMData read();
         return (extend(upper.portA.read())<<4) | (extend(lower.portA.read()));
      endmethod
   endinterface

   interface EBRPort portB;
      method Action put(UInt#(3) chip_select, Bool write, ByteAddr addr, VRAMData data_in);
         upper.portB.put(chip_select, write, addr, truncate(data_in>>4));
         lower.portB.put(chip_select, write, addr, truncate(data_in));
      endmethod

      method VRAMData read();
         return (extend(upper.portB.read())<<4) | (extend(lower.portB.read()));
      endmethod
   endinterface
endmodule : mkByteRAM

module mkByteRAMArray(Integer num_chips, ByteRAM ifc);
   if (num_chips > 8)
      error("mkByteRAMArray can only array 8 raw ByteRAMs");

   ByteRAM blocks[num_chips];
   for (Integer i=0; i<num_chips; i=i+1)
      blocks[i] <- mkByteRAM(fromInteger(i));

   DelayLine#(UInt#(3)) read_chip_A <- mkDelayLine(1);
   DelayLine#(UInt#(3)) read_chip_B <- mkDelayLine(1);

   interface EBRPort portA;
      method Action put(UInt#(3) chip_select, Bool write, ByteAddr addr, VRAMData data_in);
         for (Integer i=0; i<num_chips; i=i+1)
            blocks[i].portA.put(chip_select, write, addr, data_in);
         if (write)
            read_chip_A <= chip_select;
      endmethod
      method VRAMData read();
         if (read_chip_A.ready)
            if (read_chip_A <= fromInteger(num_chips-1))
               return blocks[read_chip_A].portA.read();
            else
               return 0;
         else
            return 0;
      endmethod
   endinterface

   interface EBRPort portB;
      method Action put(UInt#(3) chip_select, Bool write, ByteAddr addr, VRAMData data_in);
         for (Integer i=0; i<num_chips; i=i+1)
            blocks[i].portB.put(chip_select, write, addr, data_in);
         if (write)
            read_chip_B <= chip_select;
      endmethod
      method VRAMData read();
         if (read_chip_B.ready)
            if (read_chip_B <= fromInteger(num_chips-1))
               return blocks[read_chip_B].portB.read();
            else
               return 0;
         else
            return 0;
      endmethod
   endinterface
endmodule

typedef struct {
   VRAMAddr addr;
   Maybe#(VRAMData) data;
} VRAMRequest deriving (Bits, Eq);

typedef struct {
   VRAMData data;
} VRAMResponse deriving (Bits, Eq);

typedef Server#(VRAMRequest, VRAMResponse) VRAMServer;
typedef Client#(VRAMRequest, VRAMResponse) VRAMClient;

interface VRAM;
   interface VRAMServer portA;
   interface VRAMServer portB;
endinterface

module mkVRAM(Integer num_4kB_blocks, VRAM ifc);
   if (num_4kB_blocks > 32)
      error("maximum number of blocks is 32 (128KiB)");
   UInt#(TAdd#(SizeOf#(VRAMAddr), 1)) max_request_addr = fromInteger((4096 * num_4kB_blocks));

   function Tuple2#(ChipAddr, ByteAddr) split_addr(VRAMAddr a);
      UInt#(TAdd#(SizeOf#(VRAMAddr), 1)) expanded = extend(a);
      VRAMAddr wrapped = truncate(expanded % max_request_addr);
      match {.chip, .off} = split(pack(wrapped));
      return tuple2(unpack(chip), unpack(off));
   endfunction

   ByteRAM blocks[num_4kB_blocks];
   for (Integer i=0; i<num_4kB_blocks; i=i+1)
      blocks[i] <- mkByteRAM(0);

   Reg#(Maybe#(ChipAddr)) inflight_A[2] <- mkCReg(2, tagged Invalid);
   Reg#(Maybe#(ChipAddr)) inflight_B[2] <- mkCReg(2, tagged Invalid);

   interface VRAMServer portA;
      interface Put request;
         method Action put(VRAMRequest req) if (inflight_A[1] matches tagged Invalid);
            match {.chip, .off} = split_addr(req.addr);
            blocks[chip].portA.put(0, isValid(req.data), off, fromMaybe(0, req.data));
            if (!isValid(req.data))
               inflight_A[1] <= tagged Valid chip;
         endmethod
      endinterface
      interface Get response;
         method ActionValue#(VRAMResponse) get() if (inflight_A[0] matches tagged Valid .chip);
            inflight_A[0] <= tagged Invalid;
            return VRAMResponse{data: blocks[chip].portA.read()};
         endmethod
      endinterface
   endinterface

   interface VRAMServer portB;
      interface Put request;
         method Action put(VRAMRequest req) if (inflight_B[1] matches tagged Invalid);
            match {.chip, .off} = split_addr(req.addr);
            blocks[chip].portB.put(0, isValid(req.data), off, fromMaybe(0, req.data));
            if (!isValid(req.data))
               inflight_B[1] <= tagged Valid chip;
         endmethod
      endinterface
      interface Get response;
         method ActionValue#(VRAMResponse) get() if (inflight_B[0] matches tagged Valid .chip);
            inflight_B[0] <= tagged Invalid;
            return VRAMResponse{data: blocks[chip].portB.read()};
         endmethod
      endinterface
   endinterface
endmodule

endpackage