apps: Add a controller loopback throughput test app

Add a command line utility to open a transport to a BT controller, put
the controller into local loopback mode, and send and receive ACL data
packets. Record the time it takes to send and receive all packets and
calculate a throughput measurement in kB/s.

This utility is usefull for characterizing the speed of a transport to a
BT controller (such as a TCP socket or serial port) without having to
deal with a connected peer or the variability of over the air
transmissions.

The transport CLI argument is required. The packet size and packet
count arguments are optional. They default to the same values as the
bumble-bench app.

apps/controller_loopback.py

@@ -0,0 +1,197 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# -----------------------------------------------------------------------------
+# Imports
+# -----------------------------------------------------------------------------
+import asyncio
+import logging
+import os
+import time
+from bumble.colors import color
+from bumble.hci import (
+    HCI_READ_LOOPBACK_MODE_COMMAND,
+    HCI_Read_Loopback_Mode_Command,
+    HCI_WRITE_LOOPBACK_MODE_COMMAND,
+    HCI_Write_Loopback_Mode_Command,
+    LoopbackMode,
+)
+from bumble.host import Host
+from bumble.transport import open_transport_or_link
+import click
+
+
+class Loopback:
+    """Send and receive ACL data packets in local loopback mode"""
+
+    def __init__(self, packet_size: int, packet_count: int, transport: str):
+        self.transport = transport
+        self.packet_size = packet_size
+        self.packet_count = packet_count
+        self.connection_handle: int = None
+        self.connection_event = asyncio.Event()
+        self.done = asyncio.Event()
+        self.expected_cid = 0
+        self.bytes_received = 0
+        self.start_timestamp = 0
+        self.last_timestamp = 0
+
+    def on_connection(self, connection_handle: int, *args):
+        """Retrieve connection handle from new connection event"""
+        if not self.connection_event.is_set():
+            # save first connection handle for ACL
+            # subsequent connections are SCO
+            self.connection_handle = connection_handle
+            self.connection_event.set()
+
+    def on_l2cap_pdu(self, connection_handle: int, cid: int, pdu: bytes):
+        """Calculate packet receive speed"""
+        now = time.time()
+        print(f'<<< Received packet {cid}: {len(pdu)} bytes')
+        assert connection_handle == self.connection_handle
+        assert cid == self.expected_cid
+        self.expected_cid += 1
+        if cid == 0:
+            self.start_timestamp = now
+            self.last_timestamp = now
+        else:
+            elapsed_since_start = now - self.start_timestamp
+            elapsed_since_last = now - self.last_timestamp
+            self.bytes_received += len(pdu)
+            instant_rx_speed = len(pdu) / elapsed_since_last
+            average_rx_speed = self.bytes_received / elapsed_since_start
+            print(
+                color(
+                    f'@@@ RX speed: instant={instant_rx_speed:.4f},'
+                    f' average={average_rx_speed:.4f}',
+                    'cyan',
+                )
+            )
+        if self.expected_cid == self.packet_count:
+            print(color('@@@ Received last packet', 'green'))
+            self.done.set()
+
+    async def run(self):
+        """Run a loopback throughput test"""
+        print(color('>>> Connecting to HCI...', 'green'))
+        async with await open_transport_or_link(self.transport) as (
+            hci_source,
+            hci_sink,
+        ):
+            print(color('>>> Connected', 'green'))
+
+            host = Host(hci_source, hci_sink)
+            await host.reset()
+
+            # make sure data can fit in one l2cap pdu
+            l2cap_header_size = 4
+            max_packet_size = host.hc_acl_data_packet_length - l2cap_header_size
+            if self.packet_size > max_packet_size:
+                print(
+                    color(
+                        f'!!! Packet size ({self.packet_size}) larger than max supported'
+                        f' size ({max_packet_size})',
+                        'red',
+                    )
+                )
+                return
+
+            if not host.supports_command(
+                HCI_WRITE_LOOPBACK_MODE_COMMAND
+            ) or not host.supports_command(HCI_READ_LOOPBACK_MODE_COMMAND):
+                print(color('!!! Loopback mode not supported', 'red'))
+                return
+
+            # set event callbacks
+            host.on('connection', self.on_connection)
+            host.on('l2cap_pdu', self.on_l2cap_pdu)
+
+            loopback_mode = LoopbackMode.LOCAL
+
+            print(color('### Setting loopback mode', 'blue'))
+            await host.send_command(
+                HCI_Write_Loopback_Mode_Command(loopback_mode=LoopbackMode.LOCAL),
+                check_result=True,
+            )
+
+            print(color('### Checking loopback mode', 'blue'))
+            response = await host.send_command(
+                HCI_Read_Loopback_Mode_Command(), check_result=True
+            )
+            if response.return_parameters.loopback_mode != loopback_mode:
+                print(color('!!! Loopback mode mismatch', 'red'))
+                return
+
+            await self.connection_event.wait()
+            print(color('### Connected', 'cyan'))
+
+            print(color('=== Start sending', 'magenta'))
+            start_time = time.time()
+            bytes_sent = 0
+            for cid in range(0, self.packet_count):
+                # using the cid as an incremental index
+                host.send_l2cap_pdu(
+                    self.connection_handle, cid, bytes(self.packet_size)
+                )
+                print(
+                    color(
+                        f'>>> Sending packet {cid}: {self.packet_size} bytes', 'yellow'
+                    )
+                )
+                bytes_sent += self.packet_size  # don't count L2CAP or HCI header sizes
+                await asyncio.sleep(0)  # yield to allow packet receive
+
+            await self.done.wait()
+            print(color('=== Done!', 'magenta'))
+
+            elapsed = time.time() - start_time
+            average_tx_speed = bytes_sent / elapsed
+            print(
+                color(
+                    f'@@@ TX speed: average={average_tx_speed:.4f} ({bytes_sent} bytes'
+                    f' in {elapsed:.2f} seconds)',
+                    'green',
+                )
+            )
+
+
+# -----------------------------------------------------------------------------
+@click.command()
+@click.option(
+    '--packet-size',
+    '-s',
+    metavar='SIZE',
+    type=click.IntRange(8, 4096),
+    default=500,
+    help='Packet size',
+)
+@click.option(
+    '--packet-count',
+    '-c',
+    metavar='COUNT',
+    type=int,
+    default=10,
+    help='Packet count',
+)
+@click.argument('transport')
+def main(packet_size, packet_count, transport):
+    logging.basicConfig(level=os.environ.get('BUMBLE_LOGLEVEL', 'WARNING').upper())
+
+    loopback = Loopback(packet_size, packet_count, transport)
+    asyncio.run(loopback.run())
+
+
+# -----------------------------------------------------------------------------
+if __name__ == '__main__':
+    main()

bumble/hci.py

@@ -1987,6 +1987,17 @@ def type_spec(cls):
         return {'size': 1, 'mapper': lambda x: OwnAddressType(x).name}
 
 
+# -----------------------------------------------------------------------------
+class LoopbackMode(enum.IntEnum):
+    DISABLED = 0
+    LOCAL = 1
+    REMOTE = 2
+
+    @classmethod
+    def type_spec(cls):
+        return {'size': 1, 'mapper': lambda x: LoopbackMode(x).name}
+
+
 # -----------------------------------------------------------------------------
 class HCI_Packet:
     '''
@@ -3313,6 +3324,27 @@ class HCI_Read_Encryption_Key_Size_Command(HCI_Command):
     '''
 
 
+# -----------------------------------------------------------------------------
+@HCI_Command.command(
+    return_parameters_fields=[
+        ('status', STATUS_SPEC),
+        ('loopback_mode', LoopbackMode.type_spec()),
+    ],
+)
+class HCI_Read_Loopback_Mode_Command(HCI_Command):
+    '''
+    See Bluetooth spec @ 7.6.1 Read Loopback Mode Command
+    '''
+
+
+# -----------------------------------------------------------------------------
+@HCI_Command.command([('loopback_mode', 1)])
+class HCI_Write_Loopback_Mode_Command(HCI_Command):
+    '''
+    See Bluetooth spec @ 7.6.2 Write Loopback Mode Command
+    '''
+
+
 # -----------------------------------------------------------------------------
 @HCI_Command.command([('le_event_mask', 8)])
 class HCI_LE_Set_Event_Mask_Command(HCI_Command):