rocket-chip系统复位后是从bootrom中进行启动的,这章我们将详细分析rocket-chip是如何调用bootrom模块的,最后还会对复位向量进行修改,即让rocket-chip不再从bootrom开始启动,而是从我们想要的地址进行启动。
bootrom模块的调用:
首先关注的scala文件是 /src/main/scala/system/ExampleRocketSystem.scala
package freechips.rocketchip.system
import Chisel._
import freechips.rocketchip.config.Parameters
import freechips.rocketchip.diplomacy._
import freechips.rocketchip.tilelink._
import freechips.rocketchip.subsystem._
import freechips.rocketchip.devices.tilelink._
import freechips.rocketchip.util.DontTouch
/** Example Top with periphery devices and ports, and a Rocket subsystem */
class ExampleRocketSystem(implicit p: Parameters) extends RocketSubsystem
with HasAsyncExtInterrupts
with CanHaveMasterAXI4MemPort
with CanHaveMasterAXI4MMIOPort
with CanHaveSlaveAXI4Port
with HasPeripheryBootROM {
override lazy val module = new ExampleRocketSystemModuleImp(this)
// Error device used for testing and to NACK invalid front port transactions
val error = LazyModule(new TLError(p(ErrorDeviceKey), sbus.beatBytes))
// always buffer the error device because no one cares about its latency
sbus.coupleTo("slave_named_error"){ error.node := TLBuffer() := _ }
}
class ExampleRocketSystemModuleImp[+L <: ExampleRocketSystem](_outer: L) extends RocketSubsystemModuleImp(_outer)
with HasRTCModuleImp
with HasExtInterruptsModuleImp
with CanHaveMasterAXI4MemPortModuleImp
with CanHaveMasterAXI4MMIOPortModuleImp
with CanHaveSlaveAXI4PortModuleImp
with HasPeripheryBootROMModuleImp
with DontTouch
HasPeripheryBootROM & HasPeripheryBootROMModuleImp就是调用bootrom的地方。
在哪个地方可以找到呢?
答案就是 /src/main/scala/devices/tilelink/BootROM.scala
package freechips.rocketchip.devices.tilelink
import Chisel._
import freechips.rocketchip.config.{Field, Parameters}
import freechips.rocketchip.subsystem.{BaseSubsystem, HasResetVectorWire}
import freechips.rocketchip.diplomacy._
import freechips.rocketchip.tilelink._
import freechips.rocketchip.util._
import java.nio.{ByteBuffer, ByteOrder}
import java.nio.file.{Files, Paths}
/** Size, location and contents of the boot rom. */
case class BootROMParams(
address: BigInt = 0x10000,
size: Int = 0x10000,
hang: BigInt = 0x10040,
contentFileName: String)
case object BootROMParams extends Field[BootROMParams]
class TLROM(val base: BigInt, val size: Int, contentsDelayed: => Seq[Byte], executable: Boolean = true, beatBytes: Int = 4,
resources: Seq[Resource] = new SimpleDevice("rom", Seq("sifive,rom0")).reg("mem"))(implicit p: Parameters) extends LazyModule
{
val node = TLManagerNode(Seq(TLManagerPortParameters(
Seq(TLManagerParameters(
address = List(AddressSet(base, size-1)),
resources = resources,
regionType = RegionType.UNCACHED,
executable = executable,
supportsGet = TransferSizes(1, beatBytes),
fifoId = Some(0))),
beatBytes = beatBytes)))
lazy val module = new LazyModuleImp(this) {
val contents = contentsDelayed
val wrapSize = 1 << log2Ceil(contents.size)
require (wrapSize <= size)
val (in, edge) = node.in(0)
val words = (contents ++ Seq.fill(wrapSize-contents.size)(0.toByte)).grouped(beatBytes).toSeq
val bigs = words.map(_.foldRight(BigInt(0)){ case (x,y) => (x.toInt & 0xff) | y << 8})
val rom = Vec(bigs.map(x => UInt(x, width = 8*beatBytes)))
in.d.valid := in.a.valid
in.a.ready := in.d.ready
val index = in.a.bits.address(log2Ceil(wrapSize)-1,log2Ceil(beatBytes))
val high = if (wrapSize == size) UInt(0) else in.a.bits.address(log2Ceil(size)-1, log2Ceil(wrapSize))
in.d.bits := edge.AccessAck(in.a.bits, Mux(high.orR, UInt(0), rom(index)))
// Tie off unused channels
in.b.valid := Bool(false)
in.c.ready := Bool(true)
in.e.ready := Bool(true)
}
}
/** Adds a boot ROM that contains the DTB describing the system's subsystem. */
trait HasPeripheryBootROM { this: BaseSubsystem =>
val dtb: DTB
private val params = p(BootROMParams)
private lazy val contents = {
val romdata = Files.readAllBytes(Paths.get(params.contentFileName))
val rom = ByteBuffer.wrap(romdata)
rom.array() ++ dtb.contents
}
def resetVector: BigInt = params.hang
val bootrom = LazyModule(new TLROM(params.address, params.size, contents, true, sbus.control_bus.beatBytes))
sbus.control_bus.toVariableWidthSlave(Some("bootrom")){ bootrom.node }
}
/** Subsystem will power-on running at 0x10040 (BootROM) */
trait HasPeripheryBootROMModuleImp extends LazyModuleImp
with HasResetVectorWire {
val outer: HasPeripheryBootROM
global_reset_vector := outer.resetVector.U
}
由上面代码可以知道,在HasPeripheryBootROMModuleImp中有global_reset_vector := outer.resetVector.U,而在HasPeripheryBootROM中,定义的方法是def resetVector: BigInt = params.hang,最后追到params.hang是在BootROMParams中定义的,hang=0x10040。简化点就是global_reset_vector = resetVector = params.hang = 0x10040。0x10040就是bootrom的起始地址,将这个值传给了global_reset_vector,那么global_reset_vector在哪里找到呢?
答案是 /src/main/scala/subsystem/ResetVector.scala
package freechips.rocketchip.subsystem
import Chisel._
/** A single place for all tiles to find out the reset vector */
trait HasResetVectorWire {
def resetVectorBits: Int
val global_reset_vector = Wire(UInt(width = resetVectorBits))
}
那么global_reset_vector是怎么传到cpu内部的呢?
答案是 /src/main/scala/subsystem/RocketSubsystem.scala
//只复制了部分代码
class RocketSubsystemModuleImp[+L <: RocketSubsystem](_outer: L) extends BaseSubsystemModuleImp(_outer)
with HasRocketTilesModuleImp {
tile_inputs.zip(outer.hartIdList).foreach { case(wire, i) =>
wire.clock := clock
wire.reset := reset
wire.hartid := UInt(i)
wire.reset_vector := global_reset_vector
}
}
wire.reset_vector会将global_reset_vector的值传到cpu core的内部。
到这里rocket-chip从bootrom启动的大致情况已经说明完毕,下面介绍的是我自己修改的复位向量。代码修改如下,修改文件为(/src/main/scala/subsystem/RocketSubsystem.scala):
class RocketSubsystemModuleImp[+L <: RocketSubsystem](_outer: L) extends BaseSubsystemModuleImp(_outer)
with HasRocketTilesModuleImp {
tile_inputs.zip(outer.hartIdList).foreach { case(wire, i) =>
wire.clock := clock
wire.reset := reset
wire.hartid := UInt(i)
wire.reset_vector := global_reset_vector
}
//xhunter_modify
//在模块顶层声明一个为reset_vector的信号,Uint类型,input,32位
val reset_vector = IO(UInt(INPUT, width = 32))
//将reset_vector的值赋给global_reset_vector
//同时屏蔽/src/main/scala/system/ExampleRocketSystem.scala中的HasPeripheryBootROM & HasPeripheryBootROMModuleImp
global_reset_vector := reset_vector
}
用上面的方法就能使rocket-chip不再从bootrom中启动,而是从我们输入的reset_vector开始启动。