1 files changed, 91 insertions, 0 deletions
diff --git a/cpu/beta_cpu/btb.cc b/cpu/beta_cpu/btb.cc
new file mode 100644
index 000000000..bceaa66d1
--- /dev/null
+++ b/cpu/beta_cpu/btb.cc
@@ -0,0 +1,91 @@
+#include <math.h>
+
+#include "cpu/beta_cpu/btb.hh"
+#include "base/trace.hh"
+
+DefaultBTB::DefaultBTB(unsigned _numEntries,
+                       unsigned _tagBits,
+                       unsigned _instShiftAmt)
+    : numEntries(_numEntries),
+      tagBits(_tagBits),
+      instShiftAmt(_instShiftAmt)
+{
+    // @todo Check to make sure num_entries is valid (a power of 2)
+
+    DPRINTF(Fetch, "BTB: Creating BTB object.\n");
+
+    btb = new BTBEntry[numEntries];
+
+    for (int i = 0; i < numEntries; ++i)
+    {
+        btb[i].valid = false;
+    }
+
+    idxMask = numEntries - 1;
+
+    tagMask = (1 << tagBits) - 1;
+
+    tagShiftAmt = instShiftAmt + (int)log2(numEntries);
+}
+
+inline
+unsigned
+DefaultBTB::getIndex(const Addr &inst_PC)
+{
+    // Need to shift PC over by the word offset.
+    return (inst_PC >> instShiftAmt) & idxMask;
+}
+
+inline
+Addr
+DefaultBTB::getTag(const Addr &inst_PC)
+{
+    return (inst_PC >> tagShiftAmt) & tagMask;
+}
+
+bool
+DefaultBTB::valid(const Addr &inst_PC)
+{
+    unsigned btb_idx = getIndex(inst_PC);
+
+    Addr inst_tag = getTag(inst_PC);
+
+    assert(btb_idx < numEntries);
+
+    if (btb[btb_idx].valid && inst_tag == btb[btb_idx].tag) {
+        return true;
+    } else {
+        return false;
+    }
+}
+
+// @todo Create some sort of return struct that has both whether or not the
+// address is valid, and also the address.  For now will just use addr = 0 to
+// represent invalid entry.
+Addr
+DefaultBTB::lookup(const Addr &inst_PC)
+{
+    unsigned btb_idx = getIndex(inst_PC);
+
+    Addr inst_tag = getTag(inst_PC);
+
+    assert(btb_idx < numEntries);
+
+    if (btb[btb_idx].valid && inst_tag == btb[btb_idx].tag) {
+        return btb[btb_idx].target;
+    } else {
+        return 0;
+    }
+}
+
+void
+DefaultBTB::update(const Addr &inst_PC, const Addr &target)
+{
+    unsigned btb_idx = getIndex(inst_PC);
+
+    assert(btb_idx < numEntries);
+
+    btb[btb_idx].valid = true;
+    btb[btb_idx].target = target;
+    btb[btb_idx].tag = getTag(inst_PC);
+}