diff --git a/src/main/scala/devices/pwm/PWM.scala b/src/main/scala/devices/pwm/PWM.scala
index c649e7e..d46732c 100644
--- a/src/main/scala/devices/pwm/PWM.scala
+++ b/src/main/scala/devices/pwm/PWM.scala
@@ -44,16 +44,6 @@ case class PWMConfig(
   regBytes: Int = 4,
   ncmp: Int = 4,
   cmpWidth: Int = 16)
-{
-  val bc = new PWMBundleConfig(ncmp)
-}
-
-case class PWMBundleConfig(
-  ncmp: Int)
-{
-  def union(that: PWMBundleConfig): PWMBundleConfig =
-    PWMBundleConfig(scala.math.max(ncmp, that.ncmp))
-}
 
 trait HasPWMParameters {
   implicit val p: Parameters
diff --git a/src/main/scala/devices/pwm/PWMPeriphery.scala b/src/main/scala/devices/pwm/PWMPeriphery.scala
index 86e9ad2..06d3d8e 100644
--- a/src/main/scala/devices/pwm/PWMPeriphery.scala
+++ b/src/main/scala/devices/pwm/PWMPeriphery.scala
@@ -6,19 +6,20 @@ import config._
 import diplomacy.LazyModule
 import rocketchip.{TopNetwork,TopNetworkModule}
 import uncore.tilelink2.TLFragmenter
+import util.HeterogeneousBag
 
 import sifive.blocks.devices.gpio._
 
-class PWMPortIO(c: PWMBundleConfig)(implicit p: Parameters) extends Bundle {
+class PWMPortIO(c: PWMConfig)(implicit p: Parameters) extends Bundle {
   val port = Vec(c.ncmp, Bool()).asOutput
   override def cloneType: this.type = new PWMPortIO(c).asInstanceOf[this.type]
 }
 
-class PWMPinsIO(c: PWMBundleConfig)(implicit p: Parameters) extends Bundle {
+class PWMPinsIO(c: PWMConfig)(implicit p: Parameters) extends Bundle {
   val pwm = Vec(c.ncmp, new GPIOPin)
 }
 
-class PWMGPIOPort(c: PWMBundleConfig)(implicit p: Parameters) extends Module {
+class PWMGPIOPort(c: PWMConfig)(implicit p: Parameters) extends Module {
   val io = new Bundle {
     val pwm = new PWMPortIO(c).flip()
     val pins = new PWMPinsIO(c)
@@ -43,8 +44,7 @@ trait PeripheryPWMBundle {
     val p: Parameters
     val pwmConfigs: Seq[PWMConfig]
   } =>
-  val pwm_bc = pwmConfigs.map(_.bc).reduce(_.union(_))
-  val pwms = Vec(pwmConfigs.size, new PWMPortIO(pwm_bc)(p))
+  val pwms = HeterogeneousBag(pwmConfigs.map(new PWMPortIO(_)(p)))
 }
 
 trait PeripheryPWMModule {
diff --git a/src/main/scala/devices/spi/SPIPeriphery.scala b/src/main/scala/devices/spi/SPIPeriphery.scala
index f4773a2..bdd74c6 100644
--- a/src/main/scala/devices/spi/SPIPeriphery.scala
+++ b/src/main/scala/devices/spi/SPIPeriphery.scala
@@ -5,6 +5,7 @@ import Chisel._
 import diplomacy.LazyModule
 import uncore.tilelink2._
 import rocketchip.{TopNetwork,TopNetworkModule}
+import util.HeterogeneousBag
 
 trait PeripherySPI {
   this: TopNetwork { val spiConfigs: Seq[SPIConfig] } =>
@@ -18,8 +19,7 @@ trait PeripherySPI {
 
 trait PeripherySPIBundle {
   this: { val spiConfigs: Seq[SPIConfig] } =>
-  val spi_bc = spiConfigs.map(_.bc).reduce(_.union(_))
-  val spis = Vec(spiConfigs.size, new SPIPortIO(spi_bc.toSPIConfig))
+  val spis = HeterogeneousBag(spiConfigs.map(new SPIPortIO(_)))
 }
 
 trait PeripherySPIModule {
diff --git a/src/main/scala/devices/spi/TLSPI.scala b/src/main/scala/devices/spi/TLSPI.scala
index f9954ce..f93a04d 100644
--- a/src/main/scala/devices/spi/TLSPI.scala
+++ b/src/main/scala/devices/spi/TLSPI.scala
@@ -30,7 +30,6 @@ trait SPIConfigBase {
   lazy val txDepthBits = log2Floor(txDepth) + 1
   lazy val rxDepthBits = log2Floor(rxDepth) + 1
 
-  lazy val bc = new SPIBundleConfig(csWidth)
 }
 
 case class SPIConfig(
@@ -49,15 +48,6 @@ case class SPIConfig(
   require(sampleDelay >= 0)
 }
 
-case class SPIBundleConfig(csWidth: Int)
-  {
-    def union(that: SPIBundleConfig): SPIBundleConfig =
-      SPIBundleConfig(scala.math.max(csWidth, that.csWidth))
-
-    def toSPIConfig: SPIConfig = new SPIConfig(rAddress = -1,
-      csWidth = csWidth)
-  }
-
 class SPITopBundle(val i: Vec[Vec[Bool]], val r: Vec[TLBundle]) extends Bundle
 
 class SPITopModule[B <: SPITopBundle](c: SPIConfigBase, bundle: => B, outer: TLSPIBase)