diff -r bc791fa6e6dc -r f5c7429fbbde configs/common/MemConfig.py
--- a/configs/common/MemConfig.py	Fri Dec 12 17:46:46 2014 +0000
+++ b/configs/common/MemConfig.py	Fri Dec 12 17:47:09 2014 +0000
@@ -197,9 +197,15 @@
     # address mapping in the case of a DRAM
     for r in system.mem_ranges:
         for i in xrange(nbr_mem_ctrls):
-            mem_ctrls.append(create_mem_ctrl(cls, r, i, nbr_mem_ctrls,
-                                             intlv_bits,
-                                             system.cache_line_size.value))
+            mem_ctrl = create_mem_ctrl(cls, r, i, nbr_mem_ctrls, intlv_bits,
+                                       system.cache_line_size.value)
+            # Set the number of ranks based on the command-line
+            # options if it was explicitly set
+            if issubclass(cls, m5.objects.DRAMCtrl) and \
+                    options.mem_ranks:
+                mem_ctrl.ranks_per_channel = options.mem_ranks
+
+            mem_ctrls.append(mem_ctrl)
 
     system.mem_ctrls = mem_ctrls
 
diff -r bc791fa6e6dc -r f5c7429fbbde configs/common/Options.py
--- a/configs/common/Options.py	Fri Dec 12 17:46:46 2014 +0000
+++ b/configs/common/Options.py	Fri Dec 12 17:47:09 2014 +0000
@@ -90,6 +90,8 @@
                       help = "type of memory to use")
     parser.add_option("--mem-channels", type="int", default=1,
                       help = "number of memory channels")
+    parser.add_option("--mem-ranks", type="int", default=None,
+                      help = "number of memory ranks per channel")
     parser.add_option("--mem-size", action="store", type="string",
                       default="512MB",
                       help="Specify the physical memory size (single memory)")
diff -r bc791fa6e6dc -r f5c7429fbbde src/mem/dram_ctrl.cc
--- a/src/mem/dram_ctrl.cc	Fri Dec 12 17:46:46 2014 +0000
+++ b/src/mem/dram_ctrl.cc	Fri Dec 12 17:47:09 2014 +0000
@@ -92,6 +92,11 @@
     busBusyUntil(0), prevArrival(0),
     nextReqTime(0), activeRank(0), timeStampOffset(0)
 {
+    // sanity check the ranks since we rely on bit slicing for the
+    // address decoding
+    fatal_if(!isPowerOf2(ranksPerChannel), "DRAM rank count of %d is not "
+             "allowed, must be a power of two\n", ranksPerChannel);
+
     for (int i = 0; i < ranksPerChannel; i++) {
         Rank* rank = new Rank(*this, p);
         ranks.push_back(rank);