Mem: Make SimpleMemory single ported

This patch changes the simple memory to have a single slave port
rather than a vector port. The simple memory makes no attempts at
modelling the contention between multiple ports, and any such
multiplexing and demultiplexing could be done in a bus (or crossbar)
outside the memory controller. This scenario also matches with the
ongoing work on a SimpleDRAM model, which will be a single-ported
single-channel controller that can be used in conjunction with a bus
(or crossbar) to create a multi-port multi-channel controller.

There are only very few regressions that make use of the vector port,
and these are all for functional accesses only. To facilitate these
cases, memtest and memtest-ruby have been updated to also have a
"functional" bus to perform the (de)multiplexing of the functional
memory accesses.

src/mem/SimpleMemory.py

@@ -44,6 +44,6 @@ from AbstractMemory import *
 
 class SimpleMemory(AbstractMemory):
     type = 'SimpleMemory'
-    port = VectorSlavePort("Slave ports")
+    port = SlavePort("Slave ports")
     latency = Param.Latency('30ns', "Request to response latency")
     latency_var = Param.Latency('0ns', "Request to response latency variance")

src/mem/simple_mem.cc

@@ -49,24 +49,17 @@ using namespace std;
 
 SimpleMemory::SimpleMemory(const Params* p) :
     AbstractMemory(p),
-    lat(p->latency), lat_var(p->latency_var)
+    port(name() + ".port", *this), lat(p->latency), lat_var(p->latency_var)
 {
-    for (size_t i = 0; i < p->port_port_connection_count; ++i) {
-        ports.push_back(new MemoryPort(csprintf("%s-port-%d", name(), i),
-                                       *this));
-    }
 }
 
 void
 SimpleMemory::init()
 {
-    for (vector<MemoryPort*>::iterator p = ports.begin(); p != ports.end();
-         ++p) {
-        if (!(*p)->isConnected()) {
-            fatal("SimpleMemory port %s is unconnected!\n", (*p)->name());
-        } else {
-            (*p)->sendRangeChange();
-        }
+    // allow unconnected memories as this is used in several ruby
+    // systems at the moment
+    if (port.isConnected()) {
+        port.sendRangeChange();
     }
 }
 
@@ -102,22 +95,14 @@ SimpleMemory::getSlavePort(const std::string &if_name, int idx)
     if (if_name != "port") {
         return MemObject::getSlavePort(if_name, idx);
     } else {
-        if (idx >= static_cast<int>(ports.size())) {
-            fatal("SimpleMemory::getSlavePort: unknown index %d\n", idx);
-        }
-
-        return *ports[idx];
+        return port;
     }
 }
 
 unsigned int
 SimpleMemory::drain(Event *de)
 {
-    int count = 0;
-    for (vector<MemoryPort*>::iterator p = ports.begin(); p != ports.end();
-         ++p) {
-        count += (*p)->drain(de);
-    }
+    int count = port.drain(de);
 
     if (count)
         changeState(Draining);

src/mem/simple_mem.hh

@@ -54,9 +54,10 @@
 #include "params/SimpleMemory.hh"
 
 /**
- * The simple memory is a basic multi-ported memory with an infinite
- * throughput and a fixed latency, potentially with a variance added
- * to it. It uses a SimpleTimingPort to implement the timing accesses.
+ * The simple memory is a basic single-ported memory controller with
+ * an infinite throughput and a fixed latency, potentially with a
+ * variance added to it. It uses a SimpleTimingPort to implement the
+ * timing accesses.
  */
 class SimpleMemory : public AbstractMemory
 {
@@ -81,7 +82,7 @@ class SimpleMemory : public AbstractMemory
 
     };
 
-    std::vector<MemoryPort*> ports;
+    MemoryPort port;
 
     Tick lat;
     Tick lat_var;