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
此实现避免使用Vec。相反，它使用允许在每个插槽中混合信号、寄存器和逻辑定义的逻辑区。
Note that the reader API is for SpinalHDL version coming after 1.9.1
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 signal, 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
val oh = slots.map(s => s.valid && s.address === cmd.payload) // oh meaning "one hot"
when(cmd.fire) {
slots.onMask(oh){ slot =>
slot.removeIt := True
}
}
val reader = slots.reader(oh) // Create a facility to read the slots using "oh" as index
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总线（具有一致性机制）hub中，这种插槽模式用于跟踪所有正在进行的内存操作：
As well in the DRAM / SDR / DDR memory controller to implement the handling of multiple memory transactions at once (having multiple precharge / active / read / write running at the same time to improve performances) :
以及在NaxRiscv（乱序 CPU）的加载存储单元中处理存储队列/加载队列的硬件（难度有些可怕，不宜在文档中展示XD）