mem: Add tRRD as a timing parameter for the DRAM controller

This patch adds the tRRD parameter to the DRAM controller. With the
recent addition of the actAllowedAt member for each bank, this
addition is trivial.

src/mem/SimpleDRAM.py

@@ -135,6 +135,9 @@ class SimpleDRAM(AbstractMemory):
     # write-to-read turn around penalty, assumed same as read-to-write
     tWTR = Param.Latency("Write to read switching time")
 
+    # minimum row activate to row activate delay time
+    tRRD = Param.Latency("ACT to ACT delay")
+
     # time window in which a maximum number of activates are allowed
     # to take place, set to 0 to disable
     tXAW = Param.Latency("X activation window")
@@ -187,6 +190,9 @@ class DDR3_1600_x64(SimpleDRAM):
     # Greater of 4 CK or 7.5 ns, 4 CK @ 800 MHz = 5 ns
     tWTR = '7.5ns'
 
+    # Assume 5 CK for activate to activate for different banks
+    tRRD = '6.25ns'
+
     # With a 2kbyte page size, DDR3-1600 lands around 40 ns
     tXAW = '40ns'
     activation_limit = 4
@@ -239,6 +245,9 @@ class LPDDR2_S4_1066_x32(SimpleDRAM):
     # Irrespective of speed grade, tWTR is 7.5 ns
     tWTR = '7.5ns'
 
+    # Activate to activate irrespective of density and speed grade
+    tRRD = '10.0ns'
+
     # Irrespective of density, tFAW is 50 ns
     tXAW = '50ns'
     activation_limit = 4
@@ -284,6 +293,9 @@ class WideIO_200_x128(SimpleDRAM):
     # Greater of 2 CK or 15 ns, 2 CK @ 200 MHz = 10 ns
     tWTR = '15ns'
 
+    # Activate to activate irrespective of density and speed grade
+    tRRD = '10.0ns'
+
     # Two instead of four activation window
     tXAW = '50ns'
     activation_limit = 2
@@ -335,6 +347,9 @@ class LPDDR3_1600_x32(SimpleDRAM):
     # Irrespective of speed grade, tWTR is 7.5 ns
     tWTR = '7.5ns'
 
+    # Activate to activate irrespective of density and speed grade
+    tRRD = '10.0ns'
+
     # Irrespective of size, tFAW is 50 ns
     tXAW = '50ns'
     activation_limit = 4

src/mem/simple_dram.cc

@@ -70,7 +70,7 @@ SimpleDRAM::SimpleDRAM(const SimpleDRAMParams* p) :
     writeThresholdPerc(p->write_thresh_perc),
     tWTR(p->tWTR), tBURST(p->tBURST),
     tRCD(p->tRCD), tCL(p->tCL), tRP(p->tRP), tRAS(p->tRAS),
-    tRFC(p->tRFC), tREFI(p->tREFI),
+    tRFC(p->tRFC), tREFI(p->tREFI), tRRD(p->tRRD),
     tXAW(p->tXAW), activationLimit(p->activation_limit),
     memSchedPolicy(p->mem_sched_policy), addrMapping(p->addr_mapping),
     pageMgmt(p->page_policy),
@@ -988,14 +988,25 @@ SimpleDRAM::processNextReqEvent()
 }
 
 void
-SimpleDRAM::recordActivate(Tick act_tick, uint8_t rank)
+SimpleDRAM::recordActivate(Tick act_tick, uint8_t rank, uint8_t bank)
 {
     assert(0 <= rank && rank < ranksPerChannel);
     assert(actTicks[rank].size() == activationLimit);
 
     DPRINTF(DRAM, "Activate at tick %d\n", act_tick);
 
-    // if the activation limit is disabled then we are done
+    // start by enforcing tRRD
+    for(int i = 0; i < banksPerRank; i++) {
+        // next activate must not happen before tRRD
+        banks[rank][i].actAllowedAt = act_tick + tRRD;
+    }
+    // tRC should be added to activation tick of the bank currently accessed,
+    // where tRC = tRAS + tRP, this is just for a check as actAllowedAt for same
+    // bank is already captured by bank.freeAt and bank.tRASDoneAt
+    banks[rank][bank].actAllowedAt = act_tick + tRAS + tRP;
+
+    // next, we deal with tXAW, if the activation limit is disabled
+    // then we are done
     if (actTicks[rank].empty())
         return;
 
@@ -1061,24 +1072,24 @@ SimpleDRAM::doDRAMAccess(DRAMPacket* dram_pkt)
             // any waiting for banks account for in freeAt
             actTick = bank.freeAt - tCL - tRCD;
             bank.tRASDoneAt = actTick + tRAS;
-            recordActivate(actTick, dram_pkt->rank);
+            recordActivate(actTick, dram_pkt->rank, dram_pkt->bank);
 
             // sample the number of bytes accessed and reset it as
             // we are now closing this row
             bytesPerActivate.sample(bank.bytesAccessed);
             bank.bytesAccessed = 0;
         }
+        DPRINTF(DRAM, "doDRAMAccess::bank.freeAt is %lld\n", bank.freeAt);
     } else if (pageMgmt == Enums::close) {
         actTick = curTick() + addDelay + accessLat - tRCD - tCL;
-        recordActivate(actTick, dram_pkt->rank);
+        recordActivate(actTick, dram_pkt->rank, dram_pkt->bank);
 
         // If the DRAM has a very quick tRAS, bank can be made free
         // after consecutive tCL,tRCD,tRP times. In general, however,
         // an additional wait is required to respect tRAS.
         bank.freeAt = std::max(actTick + tRAS + tRP,
                 actTick + tRCD + tCL + tRP);
-
-        DPRINTF(DRAM,"doDRAMAccess::bank.freeAt is %lld\n",bank.freeAt);
+        DPRINTF(DRAM, "doDRAMAccess::bank.freeAt is %lld\n", bank.freeAt);
         bytesPerActivate.sample(burstSize);
     } else
         panic("No page management policy chosen\n");

src/mem/simple_dram.hh

@@ -420,7 +420,7 @@ class SimpleDRAM : public AbstractMemory
      * method updates the time that the banks become available based
      * on the current limits.
      */
-    void recordActivate(Tick act_tick, uint8_t rank);
+    void recordActivate(Tick act_tick, uint8_t rank, uint8_t bank);
 
     void printParams() const;
     void printQs() const;
@@ -487,6 +487,7 @@ class SimpleDRAM : public AbstractMemory
     const Tick tRAS;
     const Tick tRFC;
     const Tick tREFI;
+    const Tick tRRD;
     const Tick tXAW;
     const uint32_t activationLimit;