diff --git a/timing/cp/dma.go b/timing/cp/dma.go
index d1d321a7..454b1d1f 100644
--- a/timing/cp/dma.go
+++ b/timing/cp/dma.go
@@ -10,6 +10,54 @@ import (
 	"github.com/sarchlab/mgpusim/v3/protocol"
 )
 
+// A RequestCollection contains a single MemCopy Msg and the IDs of the Read/Write
+// requests that correspond to it, as well as the number of remaining requests
+type RequestCollection struct {
+	superiorRequest       sim.Msg
+	subordinateRequestIDs []string
+	subordinateCount      int
+}
+
+// removeIDIfExists reduces the subordinate count if a specific ID is present in the list
+// of subordinate IDs, returning true if it was and false if it was not
+func (rqC *RequestCollection) decrementCountIfExists(id string) bool {
+	for _, str := range rqC.subordinateRequestIDs {
+		if id == str {
+			rqC.subordinateCount -= 1
+			return true
+		}
+	}
+	return false
+}
+
+// isFinished returns true if the subordinate count is zero (i.e. the superior request is finished processing)
+func (rqC *RequestCollection) isFinished() bool {
+	return rqC.subordinateCount == 0
+}
+
+func (rqC *RequestCollection) getSuperior() sim.Msg {
+	return rqC.superiorRequest
+}
+
+func (rqC *RequestCollection) getSuperiorID() string {
+	return rqC.superiorRequest.Meta().ID
+}
+
+// appendSubordinateID adds a message ID to the list and increases the count
+func (rqC *RequestCollection) appendSubordinateID(id string) {
+	rqC.subordinateRequestIDs = append(rqC.subordinateRequestIDs, id)
+	rqC.subordinateCount += 1
+}
+
+func NewRequestCollection(
+	superiorRequest sim.Msg,
+) *RequestCollection {
+	rqC := new(RequestCollection)
+	rqC.superiorRequest = superiorRequest
+	rqC.subordinateCount = 0
+	return rqC
+}
+
 // A DMAEngine is responsible for accessing data that does not belongs to
 // the GPU that the DMAEngine works in.
 type DMAEngine struct {
@@ -19,7 +67,10 @@ type DMAEngine struct {
 
 	localDataSource mem.LowModuleFinder
 
-	processingReq sim.Msg
+	processingReqs []*RequestCollection
+
+	processingReq   sim.Msg
+	maxRequestCount uint64
 
 	toSendToMem []sim.Msg
 	toSendToCP  []sim.Msg
@@ -92,15 +143,28 @@ func (dma *DMAEngine) processDataReadyRsp(
 	req := dma.removeReqFromPendingReqList(rsp.RespondTo).(*mem.ReadReq)
 	tracing.TraceReqFinalize(req, dma)
 
-	processing := dma.processingReq.(*protocol.MemCopyD2HReq)
+	found := false
+	result := &RequestCollection{}
+	for _, rc := range dma.processingReqs {
+		if rc.decrementCountIfExists(req.Meta().ID) {
+			result = rc
+			found = true
+		}
+	}
+
+	if !found {
+		panic("couldn't find requestcollection")
+	}
+
+	processing := result.getSuperior().(*protocol.MemCopyD2HReq)
 
 	offset := req.Address - processing.SrcAddress
 	copy(processing.DstBuffer[offset:], rsp.Data)
 	// fmt.Printf("Dma DataReady %x, %v\n", req.Address, rsp.Data)
 
-	if len(dma.pendingReqs) == 0 {
-		tracing.TraceReqComplete(dma.processingReq, dma)
-		dma.processingReq = nil
+	if result.isFinished() {
+		tracing.TraceReqComplete(processing, dma)
+		dma.removeReqFromProcessingReqList(processing.Meta().ID)
 
 		rsp := sim.GeneralRspBuilder{}.
 			WithDst(processing.Src).
@@ -119,10 +183,23 @@ func (dma *DMAEngine) processDoneRsp(
 	r := dma.removeReqFromPendingReqList(rsp.RespondTo)
 	tracing.TraceReqFinalize(r, dma)
 
-	processing := dma.processingReq.(*protocol.MemCopyH2DReq)
-	if len(dma.pendingReqs) == 0 {
-		tracing.TraceReqComplete(dma.processingReq, dma)
-		dma.processingReq = nil
+	found := false
+	result := &RequestCollection{}
+	for _, rc := range dma.processingReqs {
+		if rc.decrementCountIfExists(r.Meta().ID) {
+			result = rc
+			found = true
+		}
+	}
+
+	if !found {
+		panic("couldn't find requestcollection")
+	}
+
+	if result.isFinished() {
+		processing := result.getSuperior().(*protocol.MemCopyH2DReq)
+		tracing.TraceReqComplete(processing, dma)
+		dma.removeReqFromProcessingReqList(processing.Meta().ID)
 
 		rsp := sim.GeneralRspBuilder{}.
 			WithDst(processing.Src).
@@ -153,8 +230,25 @@ func (dma *DMAEngine) removeReqFromPendingReqList(id string) sim.Msg {
 	return reqToRet
 }
 
+func (dma *DMAEngine) removeReqFromProcessingReqList(id string) {
+	found := false
+	newList := make([]*RequestCollection, 0, len(dma.processingReqs)-1)
+	for _, r := range dma.processingReqs {
+		if r.getSuperiorID() == id {
+			found = true
+		} else {
+			newList = append(newList, r)
+		}
+	}
+	dma.processingReqs = newList
+
+	if !found {
+		panic("not found")
+	}
+}
+
 func (dma *DMAEngine) parseFromCP(now sim.VTimeInSec) bool {
-	if dma.processingReq != nil {
+	if uint64(len(dma.processingReqs)) >= dma.maxRequestCount {
 		return false
 	}
 
@@ -164,12 +258,14 @@ func (dma *DMAEngine) parseFromCP(now sim.VTimeInSec) bool {
 	}
 	tracing.TraceReqReceive(req, dma)
 
-	dma.processingReq = req
+	rqC := NewRequestCollection(req)
+
+	dma.processingReqs = append(dma.processingReqs, rqC)
 	switch req := req.(type) {
 	case *protocol.MemCopyH2DReq:
-		dma.parseMemCopyH2D(now, req)
+		dma.parseMemCopyH2D(now, req, rqC)
 	case *protocol.MemCopyD2HReq:
-		dma.parseMemCopyD2H(now, req)
+		dma.parseMemCopyD2H(now, req, rqC)
 	default:
 		log.Panicf("cannot process request of type %s", reflect.TypeOf(req))
 	}
@@ -180,6 +276,7 @@ func (dma *DMAEngine) parseFromCP(now sim.VTimeInSec) bool {
 func (dma *DMAEngine) parseMemCopyH2D(
 	now sim.VTimeInSec,
 	req *protocol.MemCopyH2DReq,
+	rqC *RequestCollection,
 ) {
 	offset := uint64(0)
 	lengthLeft := uint64(len(req.SrcBuffer))
@@ -205,9 +302,10 @@ func (dma *DMAEngine) parseMemCopyH2D(
 			Build()
 		dma.toSendToMem = append(dma.toSendToMem, reqToBottom)
 		dma.pendingReqs = append(dma.pendingReqs, reqToBottom)
+		rqC.appendSubordinateID(reqToBottom.Meta().ID)
 
 		tracing.TraceReqInitiate(reqToBottom, dma,
-			tracing.MsgIDAtReceiver(dma.processingReq, dma))
+			tracing.MsgIDAtReceiver(req, dma))
 
 		addr += length
 		lengthLeft -= length
@@ -218,6 +316,7 @@ func (dma *DMAEngine) parseMemCopyH2D(
 func (dma *DMAEngine) parseMemCopyD2H(
 	now sim.VTimeInSec,
 	req *protocol.MemCopyD2HReq,
+	rqC *RequestCollection,
 ) {
 	offset := uint64(0)
 	lengthLeft := uint64(len(req.DstBuffer))
@@ -243,9 +342,10 @@ func (dma *DMAEngine) parseMemCopyD2H(
 			Build()
 		dma.toSendToMem = append(dma.toSendToMem, reqToBottom)
 		dma.pendingReqs = append(dma.pendingReqs, reqToBottom)
+		rqC.appendSubordinateID(reqToBottom.Meta().ID)
 
 		tracing.TraceReqInitiate(reqToBottom, dma,
-			tracing.MsgIDAtReceiver(dma.processingReq, dma))
+			tracing.MsgIDAtReceiver(req, dma))
 
 		addr += length
 		lengthLeft -= length
@@ -267,6 +367,8 @@ func NewDMAEngine(
 	dma.Log2AccessSize = 6
 	dma.localDataSource = localDataSource
 
+	dma.maxRequestCount = 4
+
 	dma.ToCP = sim.NewLimitNumMsgPort(dma, 40960000, name+".ToCP")
 	dma.ToMem = sim.NewLimitNumMsgPort(dma, 64, name+".ToMem")