Attach MemTracer to SBus , all physical addr hashed between 0X80000000->0X90000000

src/main/scala/tilelink/TracerSystemMem.scala

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+
+package freechips.rocketchip.tilelink
+
+import chisel3._
+import chisel3.util._
+import freechips.rocketchip.config.Parameters
+import freechips.rocketchip.diplomacy._
+import freechips.rocketchip.subsystem.{BaseSubsystem, CacheBlockBytes}
+import freechips.rocketchip.config.{Parameters, Field, Config}
+
+// class class, consumed by WithGPUTacer config and GPUTracerKey
+
+case class GPUTracerConfig(numLanes: Int, traceFile : String) // FIXME, add lane number and file name
+
+case object GPUTracerKey extends Field[Option[GPUTracerConfig]](None)
+
+
+
+// Both LazyModule of Tracer and Impl are both in Coalescing.scala
+
+
+//The trait is attached to DigitalTop of Chipyard system, informing it indeed has the ability 
+//to attach GPU tracer node  onto the system bus
+trait CanHaveGPUTracer { this: BaseSubsystem =>
+  implicit val p: Parameters
+
+  //p(GPUTracerKey) is the mechnimism to pass Config's parameter down to lazymodule
+  p(GPUTracerKey) .map { k =>
+    val config = p(GPUTracerKey).get
+    val tracer = LazyModule(new MemTraceDriver(config.numLanes, config.traceFile)(p))
+    // Must use :=* to ensure the N edges from Tracer doesn't get merged into 1 when connecting to SBus
+    sbus.fromPort(Some("gpu-tracer"))() :=* tracer.node
+  }
+}
+
+
+//This is used by Chip Level Config, the config which creates the SoC
+class WithGPUTracer(numLanes: Int, traceFile : String) extends Config((site, here, up) => {
+    case GPUTracerKey => Some( GPUTracerConfig(numLanes, traceFile) )
+}
+)
+
+
+
+