vram/VRAM: at last, a video RAM, with all the gubbins

To implement the mux tree that feeds into RAM ports, we need to know the
port index of the grantee to be able to wire it up. In theory we could
dispense with the per-port grant signal, but keeping it around allows
each client to deal with local concerns separate from the port routing.

vram/MemArbiter.bsv

@@ -5,7 +5,6 @@ import Vector::*;
 
 export MemArbiterOp(..);
 export MemArbiterServer(..);
-export MemArbiterClient(..);
 export MemArbiter(..), mkPriorityMemArbiter, mkRoundRobinMemArbiter;
 
 // A MemArbiterOp is an operation that a client is seeking permission
@@ -15,6 +14,8 @@ typedef struct {
    addr addr;
 } MemArbiterOp#(type addr) deriving (Bits, Eq, FShow);
 
+// mem_ops_conflict reports whether memory accesses a and b would
+// cause undefined behavior if they proceed simultaneously.
 function Bool mem_ops_conflict(Maybe#(MemArbiterOp#(addr)) a, Maybe#(MemArbiterOp#(addr)) b)
    provisos(Eq#(addr));
 
@@ -31,58 +32,39 @@ interface MemArbiterServer#(type addr);
    method Bool grant();
 endinterface
 
-// A MemArbiterClient emits requests and receives grants.
-interface MemArbiterClient#(type addr);
-   method Maybe#(MemArbiterOp#(addr)) request();
-   method Action grant();
-endinterface
-
-// Arbiter clients and servers can be connected in the obvious way.
-instance Connectable#(MemArbiterClient#(addr), MemArbiterServer#(addr));
-   module mkConnection(MemArbiterClient#(addr) client, MemArbiterServer#(addr) server, Empty ifc);
-      rule send_request (client.request matches tagged Valid .req);
-         server.request(req);
-      endrule
-
-      rule send_grant (server.grant());
-         client.grant();
-      endrule
-   endmodule
-endinstance
-
 // A MemArbiter manages concurrent access to a memory port.
 interface MemArbiter#(numeric type num_clients, type addr);
    // ports allow clients to request memory access.
    interface Vector#(num_clients, MemArbiterServer#(addr)) ports;
 
+   // granted_port returns the index in ports of the client that is
+   // being granted its request.
+   method UInt#(TLog#(num_clients)) granted_port();
+
    // The following methods are to support arbiter chaining.
    //
-   // Suppose you're arbitrating access to a dual-port
-   // memory. Typically, such a memory specifies that if one port is
-   // writing to an address, the other must not concurrently read or
-   // write that same address. This means the arbiters attached to
-   // each memory port must cooperate to avoid simultaneously granting
+   // Suppose you're arbitrating access to a dual-port memory.
+   // Typically, such a memory specifies that if one port is writing
+   // to an address, the other must not concurrently read or write
+   // that same address. This means the arbiters attached to each
+   // memory port must cooperate to avoid simultaneously granting
    // conflicting requests from their clients.
    //
-   // Calling conflict prevents the arbiter from granting a concurrent
-   // request that would result in a write-write, read-write or
-   // write-read conflict. granted_op emits the operation that the
-   // arbiter is granting, if any.
+   // conflict_in supplies an already granted operation that this
+   // arbiter must avoid conflicting with. conflict_out emits the
+   // operation that the arbiter is granting, if any.
    //
-   // MemArbiter intances are Connectable: mkConnection(a, b) gives
-   // conflict priority to a. That is, b only grants requests that
-   // don't conflict with a's grant.
+   // mkConnection(firstArbiter, secondArbiter) gives conflict
+   // priority to firstArbiter. That is, secondArbiter only grants
+   // requests that don't conflict with grants made by firstArbiter.
    (* always_ready *)
-   method Action conflict(MemArbiterOp#(addr) conflict);
-   method MemArbiterOp#(addr) granted_op();
+   method Action conflict_in(MemArbiterOp#(addr) conflict);
+   method MemArbiterOp#(addr) conflict_out();
 endinterface
 
 instance Connectable#(MemArbiter#(m, addr), MemArbiter#(n, addr));
    module mkConnection(MemArbiter#(m, addr) a, MemArbiter#(n, addr) b, Empty ifc);
-      (* fire_when_enabled *)
-      rule forward_conflict;
-         b.conflict(a.granted_op);
-      endrule
+      mkConnection(a.conflict_out, b.conflict_in);
    endmodule
 endinstance
 
@@ -91,13 +73,14 @@ endinstance
 module mkPriorityMemArbiter(MemArbiter#(num_clients, addr))
    provisos (Bits#(addr, _),
              Eq#(addr),
-             Min#(num_clients, 1, 1));
+             Min#(num_clients, 1, 1),
+             Alias#(client_idx, UInt#(TLog#(num_clients))));
 
    Vector#(num_clients, RWire#(MemArbiterOp#(addr))) reqs <- replicateM(mkRWire());
    Wire#(Vector#(num_clients, Bool)) grants <- mkBypassWire();
 
-   RWire#(MemArbiterOp#(addr)) conflict_in <- mkRWire();
-   RWire#(MemArbiterOp#(addr)) granted_op_out <- mkRWire();
+   RWire#(MemArbiterOp#(addr)) conflict_op <- mkRWire();
+   RWire#(client_idx) granted_idx <- mkRWire();
 
    (* no_implicit_conditions, fire_when_enabled *)
    rule grant_requests;
@@ -106,11 +89,11 @@ module mkPriorityMemArbiter(MemArbiter#(num_clients, addr))
 
       for (Integer i=0; i<valueOf(num_clients); i=i+1) begin
          if (reqs[i].wget() matches tagged Valid .req &&&
-             !mem_ops_conflict(conflict_in.wget(), reqs[i].wget()) &&&
+             !mem_ops_conflict(conflict_op.wget(), reqs[i].wget()) &&&
              !done) begin
                        done = True;
                        grant[i] = True;
-                       granted_op_out.wset(req);
+                       granted_idx.wset(fromInteger(i));
                     end
       end
 
@@ -125,24 +108,29 @@ module mkPriorityMemArbiter(MemArbiter#(num_clients, addr))
                   endinterface);
 
    interface ports = _ifcs;
-   method conflict = conflict_in.wset;
-   method MemArbiterOp#(addr) granted_op() if (granted_op_out.wget() matches tagged Valid .op);
+   method client_idx granted_port() if (granted_idx.wget() matches tagged Valid .idx);
+      return idx;
+   endmethod
+   method MemArbiterOp#(addr) conflict_out() if (granted_idx.wget() matches tagged Valid .idx &&&
+                                                 reqs[idx].wget() matches tagged Valid .op);
       return op;
    endmethod
+   method conflict_in = conflict_op.wset;
 endmodule
 
 typedef struct {
    Vector#(n, Bool) grant_vec;
-   Maybe#(MemArbiterOp#(addr)) granted_op;
+   Maybe#(UInt#(TLog#(n))) granted_idx;
 } GrantResult#(numeric type n, type addr) deriving (Bits, Eq, FShow);
 
 // select_grant computes which one entry of requests should be
 // granted. Priority order is descending starting from
 // requests[hipri].
 function GrantResult#(n, addr) select_grant(Vector#(n, Maybe#(MemArbiterOp#(addr))) requests,
-                                            UInt#(TLog#(n)) hipri,
+                                            client_idx hipri,
                                             Maybe#(MemArbiterOp#(addr)) conflict)
-   provisos (Eq#(addr));
+   provisos (Eq#(addr),
+             Alias#(client_idx, UInt#(TLog#(n))));
 
    function onehot(idx);
       let ret = replicate(False);
@@ -151,13 +139,15 @@ function GrantResult#(n, addr) select_grant(Vector#(n, Maybe#(MemArbiterOp#(addr
    endfunction
 
    function GrantResult#(n, addr) do_fold(GrantResult#(n, addr) acc,
-                                          Tuple2#(UInt#(TLog#(n)),
+                                          Tuple2#(client_idx,
                                                   Maybe#(MemArbiterOp#(addr))) next);
       match {.idx, .mreq} = next;
-      if (mreq matches tagged Valid .req &&& acc.granted_op matches tagged Invalid &&& !mem_ops_conflict(conflict, mreq))
+      if (mreq matches tagged Valid .req &&&
+          acc.granted_idx matches tagged Invalid &&&
+          !mem_ops_conflict(conflict, mreq))
          return GrantResult{
             grant_vec: onehot(idx),
-            granted_op: tagged Valid req
+            granted_idx: tagged Valid idx
          };
       else
          // Previous grant won, not requesting, or request not satisfiable.
@@ -168,7 +158,7 @@ function GrantResult#(n, addr) select_grant(Vector#(n, Maybe#(MemArbiterOp#(addr
    let rot = rotateBy(in, fromInteger(valueOf(n)-1)-hipri+1);
    let seed = GrantResult{
       grant_vec: replicate(False),
-      granted_op: tagged Invalid
+      granted_idx: tagged Invalid
    };
    return foldl(do_fold, seed, rot);
 endfunction
@@ -176,19 +166,20 @@ endfunction
 module mkRoundRobinMemArbiter(MemArbiter#(num_clients, addr))
    provisos (Bits#(addr, _),
              Eq#(addr),
-             Min#(num_clients, 1, 1));
+             Min#(num_clients, 1, 1),
+             Alias#(client_idx, UInt#(TLog#(num_clients))));
 
    Vector#(num_clients, RWire#(MemArbiterOp#(addr))) reqs <- replicateM(mkRWire);
    Wire#(Vector#(num_clients, Bool)) grants <- mkBypassWire();
 
-   RWire#(MemArbiterOp#(addr)) conflict_in <- mkRWire();
-   RWire#(MemArbiterOp#(addr)) granted_op_out <- mkRWire();
+   RWire#(MemArbiterOp#(addr)) conflict_op <- mkRWire();
+   RWire#(client_idx) granted_idx_out <- mkRWire();
 
    // high_prio is the index of the client that should be first in
    // line to receive access. Every time we grant access to a client,
    // the one after that in sequence becomes high_prio in the next
    // round.
-   Reg#(UInt#(TLog#(num_clients))) high_prio <- mkReg(0);
+   Reg#(client_idx) high_prio <- mkReg(0);
 
    function Maybe#(_t) get_mreq(RWire#(_t) w);
       return w.wget();
@@ -196,11 +187,11 @@ module mkRoundRobinMemArbiter(MemArbiter#(num_clients, addr))
 
    rule grant;
       let in = map(get_mreq, reqs);
-      let res = select_grant(in, high_prio, conflict_in.wget());
+      let res = select_grant(in, high_prio, conflict_op.wget());
 
       grants <= res.grant_vec;
-      if (res.granted_op matches tagged Valid .op) begin
-         granted_op_out.wset(op);
+      if (res.granted_idx matches tagged Valid .idx) begin
+         granted_idx_out.wset(idx);
          high_prio <= validValue(findElem(True, rotateR(res.grant_vec)));
       end
    endrule
@@ -213,10 +204,14 @@ module mkRoundRobinMemArbiter(MemArbiter#(num_clients, addr))
                   endinterface);
 
    interface ports = _ifcs;
-   method conflict = conflict_in.wset;
-   method MemArbiterOp#(addr) granted_op() if (granted_op_out.wget() matches tagged Valid .op);
+   method client_idx granted_port() if (granted_idx_out.wget() matches tagged Valid .idx);
+      return idx;
+   endmethod
+   method MemArbiterOp#(addr) conflict_out() if (granted_idx_out.wget() matches tagged Valid .idx &&&
+                                                reqs[idx].wget() matches tagged Valid .op);
       return op;
    endmethod
+   method conflict_in = conflict_op.wset;
 endmodule
 
 endpackage

vram/MemArbiter_Test.bsv

@@ -19,7 +19,7 @@ typedef struct {
    Maybe#(MemArbiterOp#(Addr)) conflict;
 
    Vector#(n, Bool) want_grants;
-   Maybe#(MemArbiterOp#(Addr)) want_granted_op;
+   Maybe#(MemArbiterOp#(Addr)) want_conflict_out;
 } TestCase#(numeric type n) deriving (Bits, Eq);
 
 function Maybe#(MemArbiterOp#(Addr)) read(Addr addr);
@@ -54,13 +54,13 @@ function TestCase#(n) testCase(String name,
                                Vector#(n, Maybe#(MemArbiterOp#(Addr))) reqs,
                                Maybe#(MemArbiterOp#(Addr)) conflict,
                                Vector#(n, Bool) want_grants,
-                               Maybe#(MemArbiterOp#(Addr)) want_granted_op);
+                               Maybe#(MemArbiterOp#(Addr)) want_conflict_out);
    return TestCase{
       name: name,
       reqs: reqs,
       conflict: conflict,
       want_grants: want_grants,
-      want_granted_op: want_granted_op
+      want_conflict_out: want_conflict_out
    };
 endfunction
 
@@ -84,14 +84,14 @@ module mkArbiterTB(MemArbiter#(n, Addr) dut, Vector#(m, TestCase#(n)) tests, TB
 
    (* no_implicit_conditions, fire_when_enabled *)
    rule forbid (running && isValid(tests[idx].conflict));
-      dut.conflict(validValue(tests[idx].conflict));
+      dut.conflict_in(validValue(tests[idx].conflict));
    endrule
 
-   Wire#(Maybe#(MemArbiterOp#(Addr))) got_granted_op <- mkDWire(tagged Invalid);
+   Wire#(Maybe#(MemArbiterOp#(Addr))) got_conflict_out <- mkDWire(tagged Invalid);
 
    (* fire_when_enabled *)
-   rule collect_granted_op (running);
-      got_granted_op <= tagged Valid dut.granted_op();
+   rule collect_conflict_out (running);
+      got_conflict_out <= tagged Valid dut.conflict_out();
    endrule
 
    function Fmt req_s(Maybe#(MemArbiterOp#(Addr)) v);
@@ -107,13 +107,13 @@ module mkArbiterTB(MemArbiter#(n, Addr) dut, Vector#(m, TestCase#(n)) tests, TB
       let test = tests[idx];
       let reqs = test.reqs;
       let want_grants = test.want_grants;
-      let want_granted_op = test.want_granted_op;
+      let want_conflict_out = test.want_conflict_out;
       Vector#(n, Bool) got_grants = newVector;
       for (Integer i=0; i<valueOf(n); i=i+1)
          got_grants[i] = dut.ports[i].grant();
 
       $display("RUN %s (%0d)", tests[idx].name, idx);
-      if (got_grants != want_grants || got_granted_op != want_granted_op) begin
+      if (got_grants != want_grants || got_conflict_out != want_conflict_out) begin
          $display("input:");
          for (Integer i=0; i<valueOf(n); i=i+1)
             $display("    ", $format("%0d", i), ": ", req_s(reqs[i]));
@@ -121,10 +121,10 @@ module mkArbiterTB(MemArbiter#(n, Addr) dut, Vector#(m, TestCase#(n)) tests, TB
 
          $display("  output:");
          $display("    grants: ", fshow(got_grants));
-         $display("    granted: ", fshow(got_granted_op));
+         $display("    granted: ", fshow(got_conflict_out));
 
          $display("  want grants: ", fshow(tests[idx].want_grants));
-         $display("  want granted: ", fshow(want_granted_op));
+         $display("  want granted: ", fshow(want_conflict_out));
          dynamicAssert(False, "wrong arbiter output");
       end
 

vram/VRAM.bsv

@@ -0,0 +1,99 @@
+package VRAM;
+
+import Connectable::*;
+import GetPut::*;
+import ClientServer::*;
+import Vector::*;
+import FIFOF::*;
+import SpecialFIFOs::*;
+
+import MemArbiter::*;
+import VRAMCore::*;
+
+// Re-exports from VRAMCore
+export VRAMAddr, VRAMData, VRAMRequest(..), VRAMResponse(..);
+
+export VRAMServer(..);
+export VRAM(..), mkVRAM;
+
+typedef Server#(VRAMRequest, VRAMResponse) VRAMServer;
+
+// mkArbitratedVRAMServers expands a VRAMServer port into multiple
+// ports through the use of a MemArbiter.
+module mkArbitratedVRAMServers(VRAMServer ram, MemArbiter#(n, VRAMAddr) arb, Vector#(n, VRAMServer) ifc)
+   provisos (Min#(n, 1, 1),
+             Alias#(port_idx, UInt#(TLog#(n))));
+   Vector#(n, FIFOF#(VRAMRequest)) requests <- replicateM(mkBypassFIFOF());
+   Vector#(n, FIFOF#(VRAMResponse)) responses <- replicateM(mkBypassFIFOF());
+   Reg#(Maybe#(port_idx)) awaiting_response[2] <- mkCReg(2, tagged Invalid);
+
+   (* fire_when_enabled *)
+   rule request_ports;
+      for (Integer i=0; i<valueOf(n); i=i+1)
+         if (requests[i].notEmpty) begin
+            let req = requests[i].first;
+            let arb_req = MemArbiterOp{
+               write: isValid(req.data),
+               addr: req.addr
+               };
+            arb.ports[i].request(arb_req);
+         end
+   endrule
+
+   (* fire_when_enabled *)
+   rule submit (awaiting_response[1] matches tagged Invalid);
+      let port = arb.granted_port();
+      ram.request.put(requests[port].first);
+      requests[port].deq();
+      awaiting_response[1] <= tagged Valid port;
+   endrule
+
+   (* fire_when_enabled *)
+   rule response (awaiting_response[0] matches tagged Valid .port &&& responses[port].notFull);
+      let resp <- ram.response.get();
+      responses[port].enq(resp);
+      awaiting_response[0] <= tagged Invalid;
+   endrule
+
+   return map(uncurry(toGPServer), zip(requests, responses));
+endmodule
+
+// VRAM is a GARY video RAM and its memory ports.
+interface VRAM;
+   interface VRAMServer cpu;
+   interface VRAMServer debugger;
+   interface VRAMServer palette;
+   interface VRAMServer tile1;
+   interface VRAMServer tile2;
+   interface VRAMServer sprite;
+endinterface
+
+// mkVRAM constructs a VRAM of the requested size. Memory access is
+// spread across two internal ports as follows:
+//
+// Port A: strict most-important-wins priority: CPU, then debugger,
+//         then palette DAC.
+// Port B: equal round-robin prioritization between two tile engines
+//         and the sprite engine.
+module mkVRAM(Integer num_kilobytes, VRAM ifc);
+   VRAMCore ram <- mkVRAMCore(num_kilobytes);
+
+   MemArbiter#(3, VRAMAddr) arbA <- mkPriorityMemArbiter();
+   Vector#(3, VRAMServer) portA <- mkArbitratedVRAMServers(ram.portA, arbA);
+
+   MemArbiter#(3, VRAMAddr) arbB <- mkRoundRobinMemArbiter();
+   Vector#(3, VRAMServer) portB <- mkArbitratedVRAMServers(ram.portB, arbB);
+
+   // Connect up the arbiters so they correctly prevent write-write
+   // and write-read conflicts.
+   mkConnection(arbA, arbB);
+
+   interface cpu = portA[0];
+   interface debugger = portA[1];
+   interface palette = portA[2];
+   interface tile1 = portB[0];
+   interface tile2 = portB[1];
+   interface sprite = portB[2];
+endmodule
+
+endpackage

vram/VRAMCore.bsv

@@ -1,48 +1,82 @@
 package VRAMCore;
 
-import Connectable::*;
 import GetPut::*;
 import ClientServer::*;
-import DReg::*;
-import BRAM::*;
-import Vector::*;
-import FIFOF::*;
-import SpecialFIFOs::*;
+import BRAMCore::*;
 import Real::*;
-import Printf::*;
 
 import DelayLine::*;
 import ECP5_RAM::*;
 
 export VRAMAddr;
 export VRAMData;
-export VRAMRequest;
-export VRAMResponse;
-export VRAMClient;
-export VRAMServer;
-export VRAMCore;
+export VRAMRequest(..);
+export VRAMResponse(..);
+export VRAMCore(..);
 export mkVRAMCore;
 
 typedef Bit#(8) VRAMData;
 
-// Each byte RAM we build below can address 4096 bytes, which is 12
-// address bits.
-typedef UInt#(12) ByteAddr;
-
+typedef UInt#(17) VRAMAddr;
+typedef UInt#(2) ArrayAddr;
 typedef UInt#(3) ChipAddr;
+typedef UInt#(12) ByteAddr;
 
 // ByteRAM is two EBRs glued together to make a whole-byte memory.
 typedef EBR#(ByteAddr, VRAMData, ByteAddr, VRAMData) ByteRAM;
 
+typedef struct {
+   VRAMAddr addr;
+   Maybe#(VRAMData) data;
+} VRAMRequest deriving (Bits, Eq);
+
+typedef struct {
+   VRAMData data;
+} VRAMResponse deriving (Bits, Eq);
+
+module mkNibbleRAM_ECP5(ChipAddr chip_addr, EBR#(ByteAddr, Bit#(4), ByteAddr, Bit#(4)) ifc);
+   EBRPortConfig cfg = defaultValue;
+   cfg.chip_select_addr = chip_addr;
+   let _ret <- mkEBRCore(cfg, cfg);
+   return _ret;
+endmodule
+
+module mkNibbleRAM_Sim(ChipAddr chip_addr, EBR#(ByteAddr, Bit#(4), ByteAddr, Bit#(4)) ifc);
+   BRAM_DUAL_PORT#(ByteAddr, Bit#(4)) ram <- mkBRAMCore2(4096, False);
+
+   interface EBRPort portA;
+      method Action put(UInt#(3) chip_select, Bool write, ByteAddr address, Bit#(4) datain);
+         if (chip_select == chip_addr)
+            ram.a.put(write, address, datain);
+      endmethod
+      method read = ram.a.read;
+   endinterface
+
+   interface EBRPort portB;
+      method Action put(UInt#(3) chip_select, Bool write, ByteAddr address, Bit#(4) datain);
+         if (chip_select == chip_addr)
+            ram.b.put(write, address, datain);
+      endmethod
+      method read = ram.b.read;
+   endinterface
+endmodule
+
+module mkNibbleRAM(ChipAddr chip_addr, EBR#(ByteAddr, Bit#(4), ByteAddr, Bit#(4)) ifc);
+   let _ret;
+   if (genC())
+      _ret <- mkNibbleRAM_Sim(chip_addr);
+   else
+      _ret <- mkNibbleRAM_ECP5(chip_addr);
+   return _ret;
+endmodule
+
 // 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(ChipAddr 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);
+   EBR#(ByteAddr, Bit#(4), ByteAddr, Bit#(4)) upper <- mkNibbleRAM(chip_addr);
+   EBR#(ByteAddr, Bit#(4), ByteAddr, Bit#(4)) lower <- mkNibbleRAM(chip_addr);
 
    interface EBRPort portA;
       method Action put(ChipAddr chip_select, Bool write, ByteAddr addr, VRAMData data_in);
@@ -119,25 +153,9 @@ module mkByteRAMArray(Integer num_chips, ByteRAM ifc);
    endinterface
 endmodule
 
-typedef UInt#(2) ArrayAddr;
-
-typedef UInt#(17) VRAMAddr;
-
-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 VRAMCore;
-   interface VRAMServer portA;
-   interface VRAMServer portB;
+   interface Server#(VRAMRequest, VRAMResponse) portA;
+   interface Server#(VRAMRequest, VRAMResponse) portB;
 endinterface
 
 // mkVRAMCore creates a dual port VRAM of the specified size, using
@@ -163,11 +181,7 @@ module mkVRAMCore(Integer num_kilobytes, VRAMCore ifc);
    let num_arrays = ceil(fromInteger(num_byterams) / 8);
 
    function Tuple3#(ArrayAddr, ChipAddr, ByteAddr) split_addr(VRAMAddr a);
-      if (num_bytes < 128*1024)
-         a = a % fromInteger(num_bytes);
-      match {.top, .byteaddr} = split(pack(a));
-      Tuple2#(Bit#(SizeOf#(ArrayAddr)), Bit#(SizeOf#(ChipAddr))) route = split(top);
-      return tuple3(unpack(tpl_1(route)), unpack(tpl_2(route)), unpack(byteaddr));
+      return unpack(pack(a));
    endfunction
 
    ByteRAM arrays[num_arrays];
@@ -179,7 +193,7 @@ module mkVRAMCore(Integer num_kilobytes, VRAMCore ifc);
    Reg#(Maybe#(ArrayAddr)) inflight_A[2] <- mkCReg(2, tagged Invalid);
    Reg#(Maybe#(ArrayAddr)) inflight_B[2] <- mkCReg(2, tagged Invalid);
 
-   interface VRAMServer portA;
+   interface Server portA;
       interface Put request;
          method Action put(VRAMRequest req) if (inflight_A[1] matches tagged Invalid);
             match {.array, .chip, .byteaddr} = split_addr(req.addr);
@@ -196,7 +210,7 @@ module mkVRAMCore(Integer num_kilobytes, VRAMCore ifc);
       endinterface
    endinterface
 
-   interface VRAMServer portB;
+   interface Server portB;
       interface Put request;
          method Action put(VRAMRequest req) if (inflight_B[1] matches tagged Invalid);
             match {.array, .chip, .byteaddr} = split_addr(req.addr);