xref: /XiangShan/src/main/scala/xiangshan/backend/issue/NewAgeDetector.scala (revision 527eefbd9fe4b2018a4266bd8c0e05c1b5d62327) 
1/***************************************************************************************
2 * Copyright (c) 2020-2021 Institute of Computing Technology, Chinese Academy of Sciences
3 * Copyright (c) 2020-2021 Peng Cheng Laboratory
4 *
5 * XiangShan is licensed under Mulan PSL v2.
6 * You can use this software according to the terms and conditions of the Mulan PSL v2.
7 * You may obtain a copy of Mulan PSL v2 at:
8 *          http://license.coscl.org.cn/MulanPSL2
9 *
10 * THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
11 * EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
12 * MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
13 *
14 * See the Mulan PSL v2 for more details.
15 ***************************************************************************************/
16
17package xiangshan.backend.issue
18
19import org.chipsalliance.cde.config.Parameters
20import chisel3._
21import chisel3.util._
22import xiangshan._
23import utils._
24import utility._
25
26class NewAgeDetector(numEntries: Int, numEnq: Int, numDeq: Int)(implicit p: Parameters) extends XSModule {
27  val io = IO(new Bundle {
28    val enq = Vec(numEnq, Input(Bool()))
29    val canIssue = Vec(numDeq, Input(UInt(numEntries.W)))
30    val out = Vec(numDeq, Output(UInt(numEntries.W)))
31  })
32
33  // age(i)(j): entry i enters queue before entry j
34  val age = Seq.fill(numEntries)(Seq.fill(numEntries)(RegInit(false.B)))
35  val nextAge = Seq.fill(numEntries)(Seq.fill(numEntries)(Wire(Bool())))
36
37  // to reduce reg usage, only use upper matrix
38  def get_age(row: Int, col: Int): Bool = if (row <= col) age(row)(col) else !age(col)(row)
39  def get_next_age(row: Int, col: Int): Bool = if (row <= col) nextAge(row)(col) else !nextAge(col)(row)
40
41  //only for row <= col
42  for((row, i) <- nextAge.zipWithIndex) {
43    for((elem, j) <- row.zipWithIndex) {
44      if (i == j) {
45        // an entry is always older than itself
46        elem := true.B
47      }
48      else if (i < j) {
49        when (io.enq(j)) {
50          // (1) when entry j enqueues from port k,
51          // (1.1) if entry i (<j) enqueues from previous ports, it is older than entry j
52          // (1.2) if entry i does not enqueue, set col(j) older than entry j
53          elem := true.B
54        }.elsewhen (io.enq(i)) {
55          // (2) when entry i enqueues, set row(i) to false
56          elem := false.B
57        }.otherwise {
58          // default: unchanged
59          elem := get_age(i, j)
60        }
61      }
62      else {
63        elem := !nextAge(j)(i)
64      }
65      age(i)(j) := elem
66    }
67  }
68
69  def getOldestCanIssue(get: (Int, Int) => Bool, canIssue: UInt): UInt = {
70    VecInit((0 until numEntries).map(i => {
71      (VecInit((0 until numEntries).map(j => get(i, j))).asUInt | ~canIssue).andR & canIssue(i)
72    })).asUInt
73  }
74
75  io.out.zip(io.canIssue).foreach { case (out, canIssue) =>
76    out := getOldestCanIssue(get_age, canIssue)
77  }
78}
79
80object NewAgeDetector {
81  def apply(numEntries: Int, enq: Vec[Bool], canIssue: Vec[UInt])(implicit p: Parameters): Vec[Valid[UInt]] = {
82    val age = Module(new NewAgeDetector(numEntries, enq.length, canIssue.length))
83    age.io.enq := enq
84    age.io.canIssue := canIssue
85    val outVec = Wire(Vec(canIssue.length, Valid(UInt(numEntries.W))))
86    outVec.zipWithIndex.foreach { case (out, i) =>
87      out.valid := canIssue(i).orR
88      out.bits := age.io.out(i)
89      when (out.valid) {
90        assert(PopCount(out.bits) === 1.U, s"out ($i) is not ont-hot when there is at least one entry can be issued\n")
91      }
92    }
93    outVec
94  }
95}