插槽(Slots)

简介

假设您有一些硬件必须跟踪多个相似的正在进行的活动，您可能需要实现一组“插槽”来执行此操作。此示例展示如何使用 Area 、 OHMasking.first 、 onMask 和 reader 来完成此操作。

实现

此实现不使用Vec，相反，它使用Area，从而允许在每个插槽中混合定义信号、寄存器和逻辑。

请注意， reader API 适用于1.9.1之后推出的SpinalHDL版本

package spinaldoc.examples.advanced

import spinal.core._
import spinal.lib._
import scala.language.postfixOps

case class SlotsDemo(slotsCount : Int) extends Component {
  // ...
  
  
  // Create the hardware for each slot.
  // Note each slot is an Area, not a Bundle.
  val slots = for(i <- 0 until slotsCount) yield new Area {
    // Because the slot is an Area, we can define mix signals, registers, 
    // logic definitions.
    // Here are the registers for each slots:
    val valid = RegInit(False)
    val address = Reg(UInt(8 bits))
    val age = Reg(UInt(16 bits)) // Will count since how many cycles the slot is valid

    // Here is some hardware behavior for each slots.
    // Implement the age logic.
    when(valid) {
      age := age + 1
    }

    // removeIt will be used as a slot interface later on.
    val removeIt = False
    when(removeIt) {
      valid := False
    }
  }

  // Logic to allocate a new slot.
  val insert = new Area {
    val cmd = Stream(UInt(8 bits)) // Interface to issue requests.
    val free = slots.map(!_.valid)
    val freeOh = OHMasking.first(free) // Get the first free slot (on hot mask).
    cmd.ready := free.orR // Only allow cmd when there is a free slot.
    when(cmd.fire) {
      // slots.onMask(freeOh)(code) will execute the code for each slot where
      // the corresponding freeOh bit is set
      slots.onMask(freeOh){slot =>
        slot.valid := True
        slot.address := cmd.payload
        slot.age := 0
      }
    }
  }

  // Logic to remove the slots which match a given address (assuming
  // there is not more than one match).
  val remove = new Area {
    val cmd = Flow(UInt(8 bits)) // Interface to issue requests.
    // oh meaning "one hot"
    val oh = slots.map(s => s.valid && s.address === cmd.payload)
    when(cmd.fire) {
      slots.onMask(oh){ slot =>
        slot.removeIt := True
      }
    }

    // Create a facility to read the slots using "oh" as index
    val reader = slots.reader(oh)

    val age = reader(_.age) // Age of the slot which is selected by "oh"
  }
  
  // ...
}

object SlotsDemo extends App {
  SpinalVerilog(SlotsDemo(4))
}

应用

例如，在Tilelink一致性中心中，这类槽位模式被用于追踪所有正在进行的传输中内存探针，详见 SpinalHDL代码.

以及在 DRAM / SDR / DDR 内存控制器中实现并发处理多个内存事务（同时进行预充电/激活/读/写以提高性能）：详见此处.

以及在NaxRiscv（乱序 CPU）的加载存储单元中处理存储队列/读取队列的硬件（难度有些可怕，不宜在文档中展示XD）