6 files changed, 239 insertions, 126 deletions

diff --git a/device/devices_app/usb/device_impl.cc b/device/devices_app/usb/device_impl.cc
index fd2f0ff..ae8ad40 100644
--- a/device/devices_app/usb/device_impl.cc
+++ b/device/devices_app/usb/device_impl.cc
@@ -5,7 +5,11 @@
 #include "device/devices_app/usb/device_impl.h"
 
 #include <stddef.h>
+
+#include <algorithm>
+#include <numeric>
 #include <utility>
+#include <vector>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ -128,32 +132,46 @@ void OnControlTransferOutPermissionCheckComplete(
   }
 }
 
+mojo::Array<IsochronousPacketPtr> BuildIsochronousPacketArray(
+    mojo::Array<uint32_t> packet_lengths,
+    TransferStatus status) {
+  mojo::Array<IsochronousPacketPtr> packets(packet_lengths.size());
+  for (size_t i = 0; i < packet_lengths.size(); ++i) {
+    packets[i] = IsochronousPacket::New();
+    packets[i]->length = packet_lengths[i];
+    packets[i]->status = status;
+  }
+  return packets;
+}
+
 void OnIsochronousTransferIn(
     scoped_ptr<Device::IsochronousTransferInCallback> callback,
-    uint32_t packet_size,
-    UsbTransferStatus status,
     scoped_refptr<net::IOBuffer> buffer,
-    size_t buffer_size) {
-  size_t num_packets = buffer_size / packet_size;
-  mojo::Array<mojo::Array<uint8_t>> packets(num_packets);
+    const std::vector<UsbDeviceHandle::IsochronousPacket>& packets) {
+  mojo::Array<uint8_t> data;
   if (buffer) {
-    for (size_t i = 0; i < num_packets; ++i) {
-      size_t packet_index = i * packet_size;
-      std::vector<uint8_t> bytes(packet_size);
-      std::copy(buffer->data() + packet_index,
-                buffer->data() + packet_index + packet_size, bytes.begin());
-      packets[i].Swap(&bytes);
-    }
+    // TODO(rockot/reillyg): We should change UsbDeviceHandle to use a
+    // std::vector<uint8_t> instead of net::IOBuffer. Then we could move
+    // instead of copy.
+    uint32_t buffer_size =
+        std::accumulate(packets.begin(), packets.end(), 0u,
+                        [](const uint32_t& a,
+                           const UsbDeviceHandle::IsochronousPacket& packet) {
+                          return a + packet.length;
+                        });
+    std::vector<uint8_t> bytes(buffer_size);
+    std::copy(buffer->data(), buffer->data() + buffer_size, bytes.begin());
+    data.Swap(&bytes);
   }
-  callback->Run(mojo::ConvertTo<TransferStatus>(status), std::move(packets));
+  callback->Run(std::move(data),
+                mojo::Array<IsochronousPacketPtr>::From(packets));
 }
 
 void OnIsochronousTransferOut(
     scoped_ptr<Device::IsochronousTransferOutCallback> callback,
-    UsbTransferStatus status,
     scoped_refptr<net::IOBuffer> buffer,
-    size_t buffer_size) {
-  callback->Run(mojo::ConvertTo<TransferStatus>(status));
+    const std::vector<UsbDeviceHandle::IsochronousPacket>& packets) {
+  callback->Run(mojo::Array<IsochronousPacketPtr>::From(packets));
 }
 
 }  // namespace
@@ -398,58 +416,46 @@ void DeviceImpl::GenericTransferOut(
 
 void DeviceImpl::IsochronousTransferIn(
     uint8_t endpoint_number,
-    uint32_t num_packets,
-    uint32_t packet_length,
+    mojo::Array<uint32_t> packet_lengths,
     uint32_t timeout,
     const IsochronousTransferInCallback& callback) {
   if (!device_handle_) {
-    callback.Run(TransferStatus::TRANSFER_ERROR,
-                 mojo::Array<mojo::Array<uint8_t>>());
+    callback.Run(mojo::Array<uint8_t>(),
+                 BuildIsochronousPacketArray(std::move(packet_lengths),
+                                             TransferStatus::TRANSFER_ERROR));
     return;
   }
 
   auto callback_ptr =
       make_scoped_ptr(new IsochronousTransferInCallback(callback));
   uint8_t endpoint_address = endpoint_number | 0x80;
-  size_t transfer_size = static_cast<size_t>(num_packets) * packet_length;
-  scoped_refptr<net::IOBuffer> buffer = CreateTransferBuffer(transfer_size);
-  device_handle_->IsochronousTransfer(
-      USB_DIRECTION_INBOUND, endpoint_address, buffer, transfer_size,
-      num_packets, packet_length, timeout,
-      base::Bind(&OnIsochronousTransferIn, base::Passed(&callback_ptr),
-                 packet_length));
+  device_handle_->IsochronousTransferIn(
+      endpoint_address, packet_lengths.storage(), timeout,
+      base::Bind(&OnIsochronousTransferIn, base::Passed(&callback_ptr)));
 }
 
 void DeviceImpl::IsochronousTransferOut(
     uint8_t endpoint_number,
-    mojo::Array<mojo::Array<uint8_t>> packets,
+    mojo::Array<uint8_t> data,
+    mojo::Array<uint32_t> packet_lengths,
     uint32_t timeout,
     const IsochronousTransferOutCallback& callback) {
   if (!device_handle_) {
-    callback.Run(TransferStatus::TRANSFER_ERROR);
+    callback.Run(BuildIsochronousPacketArray(std::move(packet_lengths),
+                                             TransferStatus::TRANSFER_ERROR));
     return;
   }
 
   auto callback_ptr =
       make_scoped_ptr(new IsochronousTransferOutCallback(callback));
   uint8_t endpoint_address = endpoint_number;
-  uint32_t packet_size = 0;
-  for (size_t i = 0; i < packets.size(); ++i) {
-    packet_size =
-        std::max(packet_size, static_cast<uint32_t>(packets[i].size()));
-  }
-  size_t transfer_size = packet_size * packets.size();
-  scoped_refptr<net::IOBuffer> buffer = CreateTransferBuffer(transfer_size);
-  memset(buffer->data(), 0, transfer_size);
-  for (size_t i = 0; i < packets.size(); ++i) {
-    uint8_t* packet =
-        reinterpret_cast<uint8_t*>(&buffer->data()[i * packet_size]);
-    DCHECK_LE(packets[i].size(), static_cast<size_t>(packet_size));
-    memcpy(packet, packets[i].storage().data(), packets[i].size());
+  scoped_refptr<net::IOBuffer> buffer = CreateTransferBuffer(data.size());
+  {
+    const std::vector<uint8_t>& storage = data.storage();
+    std::copy(storage.begin(), storage.end(), buffer->data());
   }
-  device_handle_->IsochronousTransfer(
-      USB_DIRECTION_OUTBOUND, endpoint_address, buffer, transfer_size,
-      static_cast<uint32_t>(packets.size()), packet_size, timeout,
+  device_handle_->IsochronousTransferOut(
+      endpoint_address, buffer, packet_lengths.storage(), timeout,
       base::Bind(&OnIsochronousTransferOut, base::Passed(&callback_ptr)));
 }
 
diff --git a/device/devices_app/usb/device_impl.h b/device/devices_app/usb/device_impl.h
index 5290fa7..2b438c8 100644
--- a/device/devices_app/usb/device_impl.h
+++ b/device/devices_app/usb/device_impl.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef DEVICE_USB_DEVICE_IMPL_H_
-#define DEVICE_USB_DEVICE_IMPL_H_
+#ifndef DEVICE_DEVICES_APP_USB_DEVICE_IMPL_H_
+#define DEVICE_DEVICES_APP_USB_DEVICE_IMPL_H_
 
 #include <stdint.h>
 
@@ -84,13 +84,13 @@ class DeviceImpl : public Device {
                           const GenericTransferOutCallback& callback) override;
   void IsochronousTransferIn(
       uint8_t endpoint_number,
-      uint32_t num_packets,
-      uint32_t packet_length,
+      mojo::Array<uint32_t> packet_lengths,
       uint32_t timeout,
       const IsochronousTransferInCallback& callback) override;
   void IsochronousTransferOut(
       uint8_t endpoint_number,
-      mojo::Array<mojo::Array<uint8_t>> packets,
+      mojo::Array<uint8_t> data,
+      mojo::Array<uint32_t> packet_lengths,
       uint32_t timeout,
       const IsochronousTransferOutCallback& callback) override;
 
@@ -110,4 +110,4 @@ class DeviceImpl : public Device {
 }  // namespace usb
 }  // namespace device
 
-#endif  // DEVICE_USB_DEVICE_IMPL_H_
+#endif  // DEVICE_DEVICES_APP_USB_DEVICE_IMPL_H_
diff --git a/device/devices_app/usb/device_impl_unittest.cc b/device/devices_app/usb/device_impl_unittest.cc
index 87324d2..e5ee893 100644
--- a/device/devices_app/usb/device_impl_unittest.cc
+++ b/device/devices_app/usb/device_impl_unittest.cc
@@ -6,9 +6,12 @@
 
 #include <stddef.h>
 #include <stdint.h>
+
 #include <map>
+#include <numeric>
 #include <queue>
 #include <set>
+#include <string>
 #include <utility>
 #include <vector>
 
@@ -34,7 +37,7 @@ namespace {
 
 class ConfigBuilder {
  public:
-  ConfigBuilder(uint8_t value) { config_.configuration_value = value; }
+  explicit ConfigBuilder(uint8_t value) { config_.configuration_value = value; }
 
   ConfigBuilder& AddInterface(uint8_t interface_number,
                               uint8_t alternate_setting,
@@ -102,21 +105,35 @@ void ExpectTransferInAndThen(TransferStatus expected_status,
   continuation.Run();
 }
 
-void ExpectPacketsAndThen(
-    TransferStatus expected_status,
-    const std::vector<std::vector<uint8_t>>& expected_packets,
-    const base::Closure& continuation,
-    TransferStatus actual_status,
-    mojo::Array<mojo::Array<uint8_t>> actual_packets) {
-  EXPECT_EQ(expected_status, actual_status);
+void ExpectPacketsOutAndThen(const std::vector<uint32_t>& expected_packets,
+                             const base::Closure& continuation,
+                             mojo::Array<IsochronousPacketPtr> actual_packets) {
   ASSERT_EQ(expected_packets.size(), actual_packets.size());
   for (size_t i = 0; i < expected_packets.size(); ++i) {
-    EXPECT_EQ(expected_packets[i].size(), actual_packets[i].size())
-        << "Packet sizes differ at index: " << i;
-    for (size_t j = 0; j < expected_packets[i].size(); ++j) {
-      EXPECT_EQ(expected_packets[i][j], actual_packets[i][j])
-          << "Contents of packet " << i << " differ at index " << j;
-    }
+    EXPECT_EQ(expected_packets[i], actual_packets[i]->transferred_length)
+        << "Packet lengths differ at index: " << i;
+    EXPECT_EQ(TransferStatus::COMPLETED, actual_packets[i]->status)
+        << "Packet at index " << i << " not completed.";
+  }
+  continuation.Run();
+}
+
+void ExpectPacketsInAndThen(const std::vector<uint8_t>& expected_bytes,
+                            const std::vector<uint32_t>& expected_packets,
+                            const base::Closure& continuation,
+                            mojo::Array<uint8_t> actual_bytes,
+                            mojo::Array<IsochronousPacketPtr> actual_packets) {
+  ASSERT_EQ(expected_packets.size(), actual_packets.size());
+  for (size_t i = 0; i < expected_packets.size(); ++i) {
+    EXPECT_EQ(expected_packets[i], actual_packets[i]->transferred_length)
+        << "Packet lengths differ at index: " << i;
+    EXPECT_EQ(TransferStatus::COMPLETED, actual_packets[i]->status)
+        << "Packet at index " << i << " not completed.";
+  }
+  ASSERT_EQ(expected_bytes.size(), actual_bytes.size());
+  for (size_t i = 0; i < expected_bytes.size(); ++i) {
+    EXPECT_EQ(expected_bytes[i], actual_bytes[i])
+        << "Contents differ at index: " << i;
   }
   continuation.Run();
 }
@@ -186,8 +203,11 @@ class USBDeviceImplTest : public testing::Test {
         .WillByDefault(Invoke(this, &USBDeviceImplTest::ControlTransfer));
     ON_CALL(mock_handle(), GenericTransfer(_, _, _, _, _, _))
         .WillByDefault(Invoke(this, &USBDeviceImplTest::GenericTransfer));
-    ON_CALL(mock_handle(), IsochronousTransfer(_, _, _, _, _, _, _, _))
-        .WillByDefault(Invoke(this, &USBDeviceImplTest::IsochronousTransfer));
+    ON_CALL(mock_handle(), IsochronousTransferIn(_, _, _, _))
+        .WillByDefault(Invoke(this, &USBDeviceImplTest::IsochronousTransferIn));
+    ON_CALL(mock_handle(), IsochronousTransferOut(_, _, _, _, _))
+        .WillByDefault(
+            Invoke(this, &USBDeviceImplTest::IsochronousTransferOut));
 
     return proxy;
   }
@@ -206,10 +226,24 @@ class USBDeviceImplTest : public testing::Test {
     mock_inbound_data_.push(data);
   }
 
+  void AddMockInboundPackets(
+      const std::vector<uint8_t>& data,
+      const std::vector<UsbDeviceHandle::IsochronousPacket>& packets) {
+    mock_inbound_data_.push(data);
+    mock_inbound_packets_.push(packets);
+  }
+
   void AddMockOutboundData(const std::vector<uint8_t>& data) {
     mock_outbound_data_.push(data);
   }
 
+  void AddMockOutboundPackets(
+      const std::vector<uint8_t>& data,
+      const std::vector<UsbDeviceHandle::IsochronousPacket>& packets) {
+    mock_outbound_data_.push(data);
+    mock_outbound_packets_.push(packets);
+  }
+
  private:
   void OpenMockHandle(const UsbDevice::OpenCallback& callback) {
     EXPECT_FALSE(is_device_open_);
@@ -336,18 +370,59 @@ class USBDeviceImplTest : public testing::Test {
       OutboundTransfer(buffer, length, callback);
   }
 
-  void IsochronousTransfer(UsbEndpointDirection direction,
-                           uint8_t endpoint,
-                           scoped_refptr<net::IOBuffer> buffer,
-                           size_t length,
-                           unsigned int packets,
-                           unsigned int packet_length,
-                           unsigned int timeout,
-                           const UsbDeviceHandle::TransferCallback& callback) {
-    if (direction == USB_DIRECTION_INBOUND)
-      InboundTransfer(callback);
-    else
-      OutboundTransfer(buffer, length, callback);
+  void IsochronousTransferIn(
+      uint8_t endpoint_number,
+      const std::vector<uint32_t>& packet_lengths,
+      unsigned int timeout,
+      const UsbDeviceHandle::IsochronousTransferCallback& callback) {
+    ASSERT_FALSE(mock_inbound_data_.empty());
+    const std::vector<uint8_t>& bytes = mock_inbound_data_.front();
+    size_t length = bytes.size();
+    scoped_refptr<net::IOBuffer> buffer = new net::IOBuffer(length);
+    std::copy(bytes.begin(), bytes.end(), buffer->data());
+    mock_inbound_data_.pop();
+
+    ASSERT_FALSE(mock_inbound_packets_.empty());
+    std::vector<UsbDeviceHandle::IsochronousPacket> packets =
+        mock_inbound_packets_.front();
+    ASSERT_EQ(packets.size(), packet_lengths.size());
+    for (size_t i = 0; i < packets.size(); ++i) {
+      EXPECT_EQ(packets[i].length, packet_lengths[i])
+          << "Packet lengths differ at index: " << i;
+    }
+    mock_inbound_packets_.pop();
+
+    callback.Run(buffer, packets);
+  }
+
+  void IsochronousTransferOut(
+      uint8_t endpoint_number,
+      scoped_refptr<net::IOBuffer> buffer,
+      const std::vector<uint32_t>& packet_lengths,
+      unsigned int timeout,
+      const UsbDeviceHandle::IsochronousTransferCallback& callback) {
+    ASSERT_FALSE(mock_outbound_data_.empty());
+    const std::vector<uint8_t>& bytes = mock_outbound_data_.front();
+    size_t length =
+        std::accumulate(packet_lengths.begin(), packet_lengths.end(), 0u);
+    ASSERT_EQ(bytes.size(), length);
+    for (size_t i = 0; i < length; ++i) {
+      EXPECT_EQ(bytes[i], buffer->data()[i]) << "Contents differ at index: "
+                                             << i;
+    }
+    mock_outbound_data_.pop();
+
+    ASSERT_FALSE(mock_outbound_packets_.empty());
+    std::vector<UsbDeviceHandle::IsochronousPacket> packets =
+        mock_outbound_packets_.front();
+    ASSERT_EQ(packets.size(), packet_lengths.size());
+    for (size_t i = 0; i < packets.size(); ++i) {
+      EXPECT_EQ(packets[i].length, packet_lengths[i])
+          << "Packet lengths differ at index: " << i;
+    }
+    mock_outbound_packets_.pop();
+
+    callback.Run(buffer, packets);
   }
 
   scoped_ptr<base::MessageLoop> message_loop_;
@@ -361,6 +436,10 @@ class USBDeviceImplTest : public testing::Test {
 
   std::queue<std::vector<uint8_t>> mock_inbound_data_;
   std::queue<std::vector<uint8_t>> mock_outbound_data_;
+  std::queue<std::vector<UsbDeviceHandle::IsochronousPacket>>
+      mock_inbound_packets_;
+  std::queue<std::vector<UsbDeviceHandle::IsochronousPacket>>
+      mock_outbound_packets_;
 
   std::set<uint8_t> claimed_interfaces_;
 
@@ -758,56 +837,52 @@ TEST_F(USBDeviceImplTest, IsochronousTransfer) {
     loop.Run();
   }
 
-  std::string outbound_packet_data = "aaaaaaaabbbbbbbbccccccccdddddddd";
-  std::vector<uint8_t> fake_outbound_packets(outbound_packet_data.size());
-  std::copy(outbound_packet_data.begin(), outbound_packet_data.end(),
-            fake_outbound_packets.begin());
+  std::vector<UsbDeviceHandle::IsochronousPacket> fake_packets(4);
+  for (size_t i = 0; i < fake_packets.size(); ++i) {
+    fake_packets[i].length = 8;
+    fake_packets[i].transferred_length = 8;
+    fake_packets[i].status = USB_TRANSFER_COMPLETED;
+  }
+  std::vector<uint32_t> fake_packet_lengths(4, 8);
+
+  std::vector<uint32_t> expected_transferred_lengths(4, 8);
+
+  std::string outbound_data = "aaaaaaaabbbbbbbbccccccccdddddddd";
+  std::vector<uint8_t> fake_outbound_data(outbound_data.size());
+  std::copy(outbound_data.begin(), outbound_data.end(),
+            fake_outbound_data.begin());
 
-  std::string inbound_packet_data = "ddddddddccccccccbbbbbbbbaaaaaaaa";
-  std::vector<uint8_t> fake_inbound_packets(inbound_packet_data.size());
-  std::copy(inbound_packet_data.begin(), inbound_packet_data.end(),
-            fake_inbound_packets.begin());
+  std::string inbound_data = "ddddddddccccccccbbbbbbbbaaaaaaaa";
+  std::vector<uint8_t> fake_inbound_data(inbound_data.size());
+  std::copy(inbound_data.begin(), inbound_data.end(),
+            fake_inbound_data.begin());
 
   AddMockConfig(ConfigBuilder(1).AddInterface(7, 0, 1, 2, 3));
-  AddMockOutboundData(fake_outbound_packets);
-  AddMockInboundData(fake_inbound_packets);
+  AddMockOutboundPackets(fake_outbound_data, fake_packets);
+  AddMockInboundPackets(fake_inbound_data, fake_packets);
 
   EXPECT_CALL(mock_handle(),
-              IsochronousTransfer(USB_DIRECTION_OUTBOUND, 0x01, _,
-                                  fake_outbound_packets.size(), 4, 8, 0, _));
+              IsochronousTransferOut(0x01, _, fake_packet_lengths, 0, _));
 
   {
     base::RunLoop loop;
-    mojo::Array<mojo::Array<uint8_t>> packets =
-        mojo::Array<mojo::Array<uint8_t>>::New(4);
-    for (size_t i = 0; i < 4; ++i) {
-      std::vector<uint8_t> bytes(8);
-      std::copy(outbound_packet_data.begin() + i * 8,
-                outbound_packet_data.begin() + i * 8 + 8, bytes.begin());
-      packets[i].Swap(&bytes);
-    }
     device->IsochronousTransferOut(
-        1, std::move(packets), 0,
-        base::Bind(&ExpectTransferStatusAndThen, TransferStatus::COMPLETED,
+        1, mojo::Array<uint8_t>::From(fake_outbound_data),
+        mojo::Array<uint32_t>::From(fake_packet_lengths), 0,
+        base::Bind(&ExpectPacketsOutAndThen, expected_transferred_lengths,
                    loop.QuitClosure()));
     loop.Run();
   }
 
   EXPECT_CALL(mock_handle(),
-              IsochronousTransfer(USB_DIRECTION_INBOUND, 0x81, _,
-                                  fake_inbound_packets.size(), 4, 8, 0, _));
+              IsochronousTransferIn(0x81, fake_packet_lengths, 0, _));
 
   {
     base::RunLoop loop;
-    std::vector<std::vector<uint8_t>> packets(4);
-    for (size_t i = 0; i < 4; ++i) {
-      packets[i].resize(8);
-      std::copy(inbound_packet_data.begin() + i * 8,
-                inbound_packet_data.begin() + i * 8 + 8, packets[i].begin());
-    }
     device->IsochronousTransferIn(
-        1, 4, 8, 0, base::Bind(&ExpectPacketsAndThen, TransferStatus::COMPLETED,
-                               packets, loop.QuitClosure()));
+        1, mojo::Array<uint32_t>::From(fake_packet_lengths), 0,
+        base::Bind(&ExpectPacketsInAndThen, fake_inbound_data,
+                   expected_transferred_lengths, loop.QuitClosure()));
     loop.Run();
   }
 
diff --git a/device/devices_app/usb/public/interfaces/device.mojom b/device/devices_app/usb/public/interfaces/device.mojom
index 438aed1..25addb2 100644
--- a/device/devices_app/usb/public/interfaces/device.mojom
+++ b/device/devices_app/usb/public/interfaces/device.mojom
@@ -139,6 +139,12 @@ enum TransferStatus {
   SHORT_PACKET,
 };
 
+struct IsochronousPacket {
+  uint32 length;
+  uint32 transferred_length;
+  TransferStatus status;
+};
+
 interface Device {
   // Retrieve a DeviceInfo struct containing metadata about the device,
   // including the set of all available device configurations.
@@ -238,22 +244,22 @@ interface Device {
   // transfers can be initiated on the endpoint. The endpoint must be of type
   // ISOCHRONOUS.
   //
-  // |packet_length| specifies the maximum expected number of bytes to receive
-  // for each packet in this transfer. |num_packets| specifies the maximum total
-  // number of packets to receive.
+  // |packet_lengths| specifies the maximum expected number of bytes to receive
+  // for each packet in this transfer.
   //
   // |timeout| specifies the request timeout in milliseconds. A timeout of 0
   // indicates no timeout: the request will remain pending indefinitely until
   // completed or otherwise terminated.
   //
-  // |packets| contains the set of packets received from the device, in order.
-  // No received packet's size will exceed |packet_length|, and will be null
-  // if |status| is neither COMPLETED, BABBLE, or SHORT_PACKET.
+  // |data| contains the data received from the device, if any. |packets|
+  // contains the status of each packet received from the device, in order. The
+  // length of the packet indicates its position in |data| while it's
+  // transferred length gives the amount of data actually received from the
+  // device.
   IsochronousTransferIn(uint8 endpoint_number,
-                        uint32 num_packets,
-                        uint32 packet_length,
+                        array<uint32> packet_lengths,
                         uint32 timeout)
-      => (TransferStatus status, array<array<uint8>>? packets);
+      => (array<uint8>? data, array<IsochronousPacket> packets);
 
   // Initiates an outbound isochronous transfer request on a specific endpoint.
   // The interface to which |endpoint_number| belongs must be claimed, and the
@@ -261,14 +267,19 @@ interface Device {
   // transfers can be initiated on the endpoint. The endpoint must be of type
   // ISOCHRONOUS.
   //
-  // |packets| specifies the series of data packets to send to the device for
-  // this transfer.
+  // |data| specifies the bytes to send to the device.
+  //
+  // |packet_lengths| specifies how |data| should be separated into packets when
+  // it is sent to the device.
   //
   // |timeout| specifies the request timeout in milliseconds. A timeout of 0
   // indicates no timeout: the request will remain pending indefinitely until
   // completed or otherwise terminated.
+
+  // |packets| contains the status of each packet sent to the device, in order.
   IsochronousTransferOut(uint8 endpoint_number,
-                         array<array<uint8>> packets,
+                         array<uint8> data,
+                         array<uint32> packet_lengths,
                          uint32 timeout)
-      => (TransferStatus status);
+      => (array<IsochronousPacket> packets);
 };
diff --git a/device/devices_app/usb/type_converters.cc b/device/devices_app/usb/type_converters.cc
index e7b2ea6..709b0ca 100644
--- a/device/devices_app/usb/type_converters.cc
+++ b/device/devices_app/usb/type_converters.cc
@@ -267,4 +267,17 @@ TypeConverter<device::usb::DeviceInfoPtr, device::UsbDevice>::Convert(
   return info;
 }
 
+// static
+device::usb::IsochronousPacketPtr
+TypeConverter<device::usb::IsochronousPacketPtr,
+              device::UsbDeviceHandle::IsochronousPacket>::
+    Convert(const device::UsbDeviceHandle::IsochronousPacket& packet) {
+  device::usb::IsochronousPacketPtr info =
+      device::usb::IsochronousPacket::New();
+  info->length = packet.length;
+  info->transferred_length = packet.transferred_length;
+  info->status = mojo::ConvertTo<device::usb::TransferStatus>(packet.status);
+  return info;
+}
+
 }  // namespace mojo
diff --git a/device/devices_app/usb/type_converters.h b/device/devices_app/usb/type_converters.h
index 59c2f4c..15484ea 100644
--- a/device/devices_app/usb/type_converters.h
+++ b/device/devices_app/usb/type_converters.h
@@ -16,8 +16,9 @@
 #include "mojo/public/cpp/bindings/array.h"
 #include "mojo/public/cpp/bindings/type_converter.h"
 
-// Type converters to convert objects between internal device/usb data types and
-// public Mojo interface data types.
+// Type converters to translate between internal device/usb data types and
+// public Mojo interface data types. This must be included by any source file
+// that uses these conversions explicitly or implicitly.
 
 namespace device {
 class UsbDevice;
@@ -121,6 +122,13 @@ struct TypeConverter<device::usb::DeviceInfoPtr, device::UsbDevice> {
   static device::usb::DeviceInfoPtr Convert(const device::UsbDevice& device);
 };
 
+template <>
+struct TypeConverter<device::usb::IsochronousPacketPtr,
+                     device::UsbDeviceHandle::IsochronousPacket> {
+  static device::usb::IsochronousPacketPtr Convert(
+      const device::UsbDeviceHandle::IsochronousPacket& packet);
+};
+
 }  // namespace mojo
 
 #endif  // DEVICE_DEVICES_APP_USB_TYPE_CONVERTERS_H_