Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/nccgroup/sniffle

A sniffer for Bluetooth 5 and 4.x LE
https://github.com/nccgroup/sniffle

Last synced: about 16 hours ago
JSON representation

A sniffer for Bluetooth 5 and 4.x LE

Awesome Lists containing this project

README 

        
# Sniffle



**Sniffle is a sniffer for Bluetooth 5 and 4.x (LE) using TI CC1352/CC26x2 hardware.**



Sniffle has a number of useful features, including:



* Support for BT5/4.2 extended length advertisement and data packets

* Support for BT5 Channel Selection Algorithms #1 and #2

* Support for all BT5 PHY modes (regular 1M, 2M, and coded modes)

* Support for sniffing only advertisements and ignoring connections

* Support for channel map, connection parameter, and PHY change operations

* Support for advertisement filtering by MAC address and RSSI

* Support for BT5 extended advertising (non-periodic)

* Support for capturing advertisements from a target MAC on all three primary

  advertising channels using a single sniffer. **This makes connection detection

  nearly 3x more reliable than most other sniffers that only sniff one advertising

  channel.**

* Easy to extend host-side software written in Python

* PCAP export compatible with the Ubertooth

* Wireshark compatible plugin



## Prerequisites



* Any of the following hardware devices (functionally equivalent for Sniffle)

    * TI CC26x2R Launchpad Board: 

    * TI CC2652RB Launchpad Board: 

    * TI CC1352R Launchpad Board: 

    * TI CC1352P Launchpad Board: 

    * TI CC2652R7 Launchpad Board: 

    * TI CC1352P7 Launchpad Board: 

    * TI CC2651P3 Launchpad Board: 

    * TI CC1354P10 Launchpad Board: 

    * SONOFF CC2652P USB Dongle Plus: 

    * EC Catsniffer V3 CC1352 & RP2040 

* ARM GNU Toolchain for AArch32 bare-metal target (arm-none-eabi): 

* TI SimpleLink Low Power F2 SDK 7.41.00.17: 

* TI DSLite Programmer Software: see below

* Python 3.9+ with PySerial installed



**If you don't want to go through the effort of setting up a build

environment for the firmware, you can just flash prebuilt firmware binaries

using UniFlash/DSLite.** Prebuilt firmware binaries are attached to releases

on the GitHub releases tab of this project. When using prebuilt firmware, be

sure to use the Python code corresponding to the release tag rather than master

to avoid compatibility issues with firmware that is behind the master branch.



### Installing GCC



The `arm-none-eabi-gcc` provided through various Linux distributions' package

manager often lacks some header files or requires some changes to linker

configuration. For minimal hassle, I suggest using the ARM GCC linked above.

You can just download and extract the prebuilt executables.



### Installing the TI SDK



The TI SDK is provided as an executable binary that extracts a bunch of source

code once you accept the license agreement. On Linux and Mac, the default

installation directory is inside`~/ti/`. This works fine and my makefiles

expect this path, so I suggest just going with the default here. The same

applies for the TI SysConfig tool.



Once the SDK has been extracted, you will need to edit one makefile to match

your build environment. Within `~/ti/simplelink_cc13xx_cc26xx_sdk_7_41_00_17`

(or wherever the SDK was installed) there is a makefile named `imports.mak`.

The only paths that need to be set here to build Sniffle are for GCC, XDC,

cmake and SysConfig. We don't need the CCS compiler. See the diff below as

an example, and adapt for wherever you installed things.



```

diff --git a/imports.mak b/imports.mak

index d3900b5b6..e7108c3df 100644

--- a/imports.mak

+++ b/imports.mak

@@ -18,14 +18,14 @@

 # will build using each non-empty *_ARMCOMPILER cgtool.

 #

 

-XDC_INSTALL_DIR        ?= /home/username/ti/xdctools_3_62_01_15_core

-SYSCONFIG_TOOL         ?= /home/username/ti/ccs1230/ccs/utils/sysconfig_1.18.1/sysconfig_cli.sh

+XDC_INSTALL_DIR        ?= $(HOME)/ti/xdctools_3_62_01_15_core

+SYSCONFIG_TOOL         ?= $(HOME)/ti/sysconfig_1.18.1/sysconfig_cli.sh

 

-CMAKE                  ?= /home/username/cmake-3.21.3/bin/cmake

+CMAKE                  ?= cmake

 PYTHON                 ?= python3

 

 TICLANG_ARMCOMPILER    ?= /home/username/ti/ccs1230/ccs/tools/compiler/ti-cgt-armllvm_3.2.0.LTS-0

-GCC_ARMCOMPILER        ?= /home/username/arm-none-eabi-gcc/9.2019.q4.major-0

+GCC_ARMCOMPILER        ?= $(HOME)/arm_tools/arm-gnu-toolchain-13.3.rel1-x86_64-arm-none-eabi

 IAR_ARMCOMPILER        ?= /home/username/iar9.40.2

 

 # Uncomment this to enable the TFM build

```



### Obtaining DSLite



DSLite is TI's command line programming and debug server tool for XDS110

debuggers. The CC26xx and CC13xx Launchpad boards both include XDS110 debuggers.

Unfortunately, TI does not provide a standalone command line DSLite download.

The easiest way to obtain DSLite is to install [UniFlash](http://www.ti.com/tool/download/UNIFLASH)

from TI. It's available for Linux, Mac, and Windows. The DSLite executable will

be located at `deskdb/content/TICloudAgent/linux/ccs_base/DebugServer/bin/DSLite`

relative to the UniFlash installation directory. On Linux, the default UniFlash

installation directory is inside `~/ti/`.



You should place the DSLite executable directory within your `$PATH`.



## Firmware Building



Once the GCC, DSLite, and the SDK is installed and operational, building

Sniffle should be straight forward. Just navigate to the `fw` directory and

run `make`. If you didn't install the SDK to the default directory, you may

need to edit `SIMPLELINK_SDK_INSTALL_DIR` in the makefile.



If building for or installing on a some variant of Launchpad other than CC26x2R,

you must specify `PLATFORM=xxx`, either as an argument to make, or by defining

it as an environment variable prior to invoking make. Supported values for `PLATFORM`

can be found in the firmware makefile. Be sure to perform a `make clean` before

building for a different platform.



## Firmware Installation (TI Launchpad Board)



To install Sniffle on a (plugged in) CC26x2R Launchpad using DSLite, run

`make load` within the `fw` directory. For any other Launchpad models, you must

specify the `PLATFORM` argument to make as descirbed above. You can also flash

the compiled `sniffle.hex` binary using the UniFlash GUI.



## Firmware Installation (SONOFF USB Dongle)



To install Sniffle on a SONOFF CC2652P dongle (equipped with a CP2102 USB/UART

bridge), you need to use a special firmware build that uses a 921600 baud rate

(labelled `1M`) instead of the default 2 megabit baud rate. You can use

[JelmerT/cc2538-bsl](https://github.com/JelmerT/cc2538-bsl) to flash the firmware

using the built-in ROM bootloader with the following command:



```

python3 cc2538-bsl.py -p /dev/ttyUSB0 --bootloader-sonoff-usb -ewv sniffle_cc1352p1_cc2652p1_1M.hex

```



As of April 23, 2024, there are a couple bugs in `cc2538-bsl` for which

pull requests [168](https://github.com/JelmerT/cc2538-bsl/pull/168) and

[173](https://github.com/JelmerT/cc2538-bsl/pull/173) need to be merged to fix.

In the interim, while waiting for those pull requests to be merged, you can use

my fork at .



**WARNING:** Do not flash the wrong build variant using the bootloader, or you

risk bricking the device and locking yourself out of the bootloader. For Sonoff

CC2652P devices, use the `sniffle_cc1352p1_cc2652p1_1M.hex` file (`CC2652P1F_1M`

build variant). If you flash the wrong variant and lock yourself out of the

bootloader, it may be possible to recover the device using JTAG/SWD.



Newer Sonoff dongles contain a CP2102N instead of the old CP2102. The CP2102N

supports higher baud rates, including 2M and 3M baud. However, there is no easy

and cross-platform way to distinguish between the CP2102 and CP2102N in software.

Thus, the Sniffle host software expects the `1M` (921600 baud) firmware on all

devices with a CP2102/CP2102N USB/UART bridge. This slower baud rate should be fine

for nearly all use cases, though in theory it may be possible to saturate the

UART interface with the 2M PHY. If you really want to use the full 2M baud rate

on your newer CP2102N equipped Sonoff (or other brand) dongle, you can flash the

full baud rate firmware and modify `sniffle_hw.py` to not lower the baud rate for

CP2102 devices.



## Firmware Installation (Catsniffer V3)



Electronic Cats provides a Catnip Uploader tool for loading firmware. For detailed information,

refer to the [repository](https://github.com/ElectronicCats/CatSniffer-Tools/tree/main).

Download the tool and follow these commands:



```bash

# Fetch the CatSniffer tools and their dependencies

[ec@sniffle]$ git clone https://github.com/ElectronicCats/CatSniffer-Tools.git

[ec@sniffle]$ cd CatSniffer-Tools/catnip_uploader

[ec@sniffle]$ pip install -r requirements.txt



# Download the available firmwares

[ec@sniffle]$ python3 catnip_uploader.py releases

[INFO] Fetching assets from https://api.github.com/repos/ElectronicCats/CatSniffer-Firmware/releases/latest

[INFO] Release: board-v3.x-v1.1.0

[INFO] Fetching assets from https://api.github.com/repos/nccgroup/Sniffle/releases/latest

[INFO] Release: v1.10.0

[INFO] Found local release: releases_board-v3.x-v1.1.0

[SUCCESS] Local release is up to date: board-v3.x-v1.1.0

[SUCCESS] Available releases:

0: sniffer_fw_CC1352P_7_v1.10.hex

1: airtag_scanner_CC1352P_7_v1.0.hex

2: nccgroup_v1.10.0_sniffle_cc1352p7_1M.hex

3: airtag_spoofer_CC1352P_7_v1.0.hex

4: sniffle_CC1352P_7_v1.7.hex



# Install the firmware

[ec@sniffle]$ python3 catnip_uploader.py load 2 COMPORT

```



You need to change the *COMPORT* to the appropriate path for your board.

Using the command `python3 catnip_uploader.py load 2 COMPORT`, you will load

the `2: nccgroup_v1.10.0_sniffle_cc1352p7_1M.hex` firmware.

**To load the firmware Catsniffer V3 requires SerialPassthroughwithboot**.



**WARNING:** Do not flash the wrong build variant using the bootloader, or you

risk bricking the device and locking yourself out of the bootloader. If you

use the `catnip_uploader.py` script to fetch and install the firmware, it will

only present compatible firmware. However, if you choose to compile and install

the firmware manually, be sure you use the correct build variant. For CatSniffer

v3 devices, use the `sniffle_cc1352p7_1M.hex` file (`CC1352P74_1M` build variant).

CatSniffer v1.x/v2.x devices use a different chip variant (CC1352P1) that needs a

different firmware build (`CC1352P1F3_1M` variant, `sniffle_cc1352p1_cc2652p1_1M.hex`

image). Sniffle has not been tested on CatSniffer v1.x/v2.x devices but they will

probably work as long as you flash the appropriate build variant. If you flash the

wrong variant and lock yourself out of the bootloader, it may be possible to recover

the device using JTAG/SWD.



## Sniffer Usage



```

[skhan@serpent python_cli]$ ./sniff_receiver.py --help

usage: sniff_receiver.py [-h] [-s SERPORT] [-c {37,38,39}] [-p] [-r RSSI] [-m MAC] [-i IRK]

                         [-S STRING] [-a] [-A] [-e] [-H] [-l] [-q] [-Q PRELOAD] [-n] [-C]

                         [-d] [-o OUTPUT]



Host-side receiver for Sniffle BLE5 sniffer



options:

  -h, --help            show this help message and exit

  -s SERPORT, --serport SERPORT

                        Sniffer serial port name

  -c {37,38,39}, --advchan {37,38,39}

                        Advertising channel to listen on

  -p, --pause           Pause sniffer after disconnect

  -r RSSI, --rssi RSSI  Filter packets by minimum RSSI

  -m MAC, --mac MAC     Filter packets by advertiser MAC

  -i IRK, --irk IRK     Filter packets by advertiser IRK

  -S STRING, --string STRING

                        Filter for advertisements containing the specified string

  -a, --advonly         Passive scanning, don't follow connections

  -A, --scan            Active scanning, don't follow connections

  -e, --extadv          Capture BT5 extended (auxiliary) advertising

  -H, --hop             Hop primary advertising channels in extended mode

  -l, --longrange       Use long range (coded) PHY for primary advertising

  -q, --quiet           Don't display empty packets

  -Q PRELOAD, --preload PRELOAD

                        Preload expected encrypted connection parameter changes

  -n, --nophychange     Ignore encrypted PHY mode changes

  -C, --crcerr          Capture packets with CRC errors

  -d, --decode          Decode advertising data

  -o OUTPUT, --output OUTPUT

                        PCAP output file name

```



The XDS110 debugger on the Launchpad boards creates two serial ports. On

Linux, they are typically named `ttyACM0` and `ttyACM1`. The first of the

two created serial ports is used to communicate with Sniffle. By default,

the Python CLI communicates using the first CDC-ACM device it sees matching

the TI XDS110 USB VID:PID combo, or the first Sonoff dongle it sees. You

may need to override this with the `-s` command line option if you are using

a different USB serial adapter or have additional USB CDC-ACM devices connected.



For the `-r` (RSSI filter) option, a value of -40 tends to work well if the

sniffer is very close to or nearly touching the transmitting device. The RSSI

filter is very useful for ignoring irrelevant advertisements in a busy RF

environment. The RSSI filter is only active when capturing advertisements,

as you always want to capture data channel traffic for a connection being

followed. You probably don't want to use an RSSI filter when MAC filtering

is active, as you may lose advertisements from the MAC address of interest

when the RSSI is too low.



To hop along with advertisements and have reliable connection sniffing, you

need to set up a MAC filter with the `-m` option. You should specify the

MAC address of the peripheral device, not the central device. To figure out

which MAC address to sniff, you can run the sniffer with RSSI filtering while

placing the sniffer near the target. This will show you advertisements from

the target device including its MAC address. It should be noted that many BLE

devices advertise with a randomized MAC address rather than their "real" fixed

MAC written on a label.



Most new BLE devices use Resolvable Private Addresses (RPAs) rather than fixed

static or public addresses. While you can set up a MAC filter to a particular

RPA, devices periodically change their RPA. RPAs can can be resolved (associated

with a particular device) if the Identity Resolving Key (IRK) is known. Sniffle

supports automated RPA resolution when the IRK is provided. This avoids the need

to keep updating the MAC filter whenever the RPA changes. You can specify an

IRK for Sniffle with the `-i` option; the IRK should be provided in hexadecimal

format, with the most significant byte (MSB) first. Specifying an IRK allows

Sniffle to channel hop with an advertiser the same way it does with a MAC filter.

The IRK based MAC filtering feature (`-i`) is mutually exclusive with the static

MAC filtering feature (`-m`).



There is also a convenience feature to automatically identify the MAC address

of the advertiser whose advertisement or scan response contains a specified

string (series of bytes). This is useful for devices with RPAs where the IRK is

unknown, but the advertisement contains a sufficiently unique static string suitable

for identification. This feature uses the `-S` option, with the string specified

using standard escape sequences. For example, to look for an advertiser whose

advertisement contains the hex byte sequence DE AD BE EF, specify

`-S "\xDE\xAD\xBE\xEF"`. To look for an advertiser with the string "hello",

simply specify `-S "hello"`. When the string search feature is used, initially

all MAC addresses will be accepted till an advertisement containing the search

string is found. After that, a MAC filter will be set up with the corresponding

advertiser's MAC address, and any RSSI filter would be automatically disabled.



To enable following auxiliary pointers in Bluetooth 5 extended advertising,

enable the `-e` option. To improve performance and reliability in extended

advertising capture, this option disables hopping on the primary advertising

channels, even when a MAC filter is set up. If you are unsure whether a

connection will be established via legacy or extended advertising, you can

enable the `-H` flag in conjunction with `-e` to perform primary channel

hopping with legacy advertisements, and scheduled listening to extended

advertisement auxiliary packets. When combining `-e` and `-H`, the

reliability of connection detection may be reduced compared to hopping on

primary (legacy) or secondary (extended) advertising channels alone.



To sniff the long range PHY on primary advertising channels, specify the `-l`

option. Note that no hopping between primary advertising channels is supported

in long range mode, since all long range advertising uses the BT5 extended

mechanism. Under the extended mechanism, auxiliary pointers on all three

primary channels point to the same auxiliary packet, so hopping between

primary channels is unnecessary.



To not print empty data packets on screen while following a connection, use

the `-q` flag. This makes it easier to observe meaningful communications in

real time, but may obscure when connection following is flaky or lost.



For encrypted connections, Sniffle supports detecting connection parameter

updates even when the encryption key is unknown, and it attempts to measure

the new parameters. However, if you know the new connection interval and Instant

delta to expect in encrypted connection parameter updates, you can specify them

with the `--preload`/`-Q` option to improve performance/reliability.

The expected Interval:DeltaInstant pair should be provided as colon separated

integers. Interval is an integer representing multiples of 1.25 ms (as defined

in LL\_CONNECTION\_UPDATE\_IND). DeltaInstant is the number of connection events

between when the connection update packet is transmitted and when the new

parameters are applied. DeltaInstant must be greater than or equal to 6, as per

the Bluetooth specification's requirements for master devices. If multiple

encrypted parameter updates are expected, you can provide multiple parameter

pairs, separated by commas (eg. `6:7,39:8`). If you have a device that issues

encrypted PHY update PDUs that don't change the PHY, or puts out encrypted LE

power control PDUs without any PHY changes, you can use the `--nophychange`/`-n`

option.



To stop the sniffer, press Ctrl-C.



If for some reason the sniffer firmware locks up and refuses to capture any

traffic even with filters disabled, you should reset the sniffer MCU. On

Launchpad boards, the reset button is located beside the micro USB port.



## Scanner Usage



```

usage: scanner.py [-h] [-s SERPORT] [-c {37,38,39}] [-r RSSI] [-l]



Scanner utility for Sniffle BLE5 sniffer



optional arguments:

  -h, --help            show this help message and exit

  -s SERPORT, --serport SERPORT

                        Sniffer serial port name

  -c {37,38,39}, --advchan {37,38,39}

                        Advertising channel to listen on

  -r RSSI, --rssi RSSI  Filter packets by minimum RSSI

  -l, --longrange       Use long range (coded) PHY for primary advertising

  -o OUTPUT, --output OUTPUT

                        PCAP output file name

```



The scanner command line arguments work the same as the sniffer. The purpose of

the scanner utility is to gather a list of nearby devices advertising, and

actively issue scan requests for observed devices, without having the deluge

of fast scrolling data you get with the sniffer utility. The hardware/firmware

will enter an active scanning mode where it will report received advertisements,

issue scan requests for scannable ones, and report received scan responses.

The scanner utility will record and report observed MAC addresses only once

without spamming the display. Once you're done capturing advertisements, press

Ctrl-C to stop scanning and report the results. The scanner will show the last

advertisement and scan response from each target. Scan results will be sorted

by RSSI in descending order.



## Usage Examples



Sniff all advertisements on channel 38, ignore RSSI < -50, stay on advertising

channel even when CONNECT\_REQs are seen.



```

./sniff_receiver.py -c 38 -r -50 -a

```



Sniff advertisements from MAC 12:34:56:78:9A:BC, stay on advertising channel

even when CONNECT\_REQs are seen, save advertisements to `data1.pcap`.



```

./sniff_receiver.py -m 12:34:56:78:9A:BC -a -o data1.pcap

```



Sniff advertisements and connections for the first MAC address seen with

RSSI >= -40. The RSSI filter will be disabled automatically once a MAC address

has been locked onto. Save captured data to `data2.pcap`.



```

./sniff_receiver.py -m top -r -40 -o data2.pcap

```



Sniff advertisements and connections from the peripheral with big endian IRK

4E0BEA5355866BE38EF0AC2E3F0EBC22. Preload two expected encrypted connection

parameter updates; the first with an Interval of 6, occuring at an instant 6

connection events after an encrypted LL\_CONNECTION\_UPDATE\_IND is observed

by the sniffer. The second expected encrypted connection update has an Interval

of 39, and DeltaInstant of 6 too.



```

./sniff_receiver.py -i 4E0BEA5355866BE38EF0AC2E3F0EBC22 -Q 6:6,39:6

```



Sniff BT5 extended advertisements and connections from nearby (RSSI >= -55) devices.



```

./sniff_receiver.py -r -55 -e

```



Sniff legacy and extended advertisements and connections from the device with the

specified MAC address. Save captured data to `data3.pcap`.



```

./sniff_receiver.py -eH -m 12:34:56:78:9A:BC -o data3.pcap

```



Sniff extended advertisements and connections using the long range primary PHY on

channel 38.



```

./sniff_receiver.py -le -c 38

```



Actively scan on channel 39 for advertisements with RSSI greater than -50.



```

./scanner.py -c 39 -r -50

```



## Obtaining the IRK



If you have a rooted Android phone, you can find IRKs (and LTKs) in the Bluedroid

configuration file. On Android 8.1, this is located at `/data/misc/bluedroid/bt_config.conf`.

The `LE_LOCAL_KEY_IRK` specifies the Android device's own IRK, and the first 16

bytes of `LE_KEY_PID` for every bonded device in the file indicate the bonded

device's IRK. Be aware that keys stored in this file are little endian, so

**the byte order of keys in this file will need to be reversed.** For example,

the little endian IRK 22BC0E3F2EACF08EE36B865553EA0B4E needs to be changed to

4E0BEA5355866BE38EF0AC2E3F0EBC22 (big endian) when being passed to Sniffle with

the `-i` option.



You can also find the IRK and LTK through HCI Snoop logs captured on Android or iOS

without rooting the device:



* Android: 

* iOS: 



## Wireshark Plugin



Sniffle includes a Wireshark plugin that makes it possible to launch Sniffle automatically

from the Wireshark GUI by selecting the 'Sniffle' capture interface.



To install the Sniffle plugin, first find the location of your Personal Extcap folder in the

'About Wireshark' dialog (*Help* > *About Wireshark* > *Folders* > *Personal Extcap path*).

On POSIX (Linux and Mac OS) systems running recent versions of Wireshark (4.2.0+), this

folder is located at `~/.local/lib/wireshark/extcap`. Under Windows, it can be found at

`%USERPROFILE%\AppData\Roaming\Wireshark\extcap`.



On POSIX systems, you can just symlink the Sniffle extcap plugin into the Wireshark personal

extcap directory:



```

mkdir -p ~/.local/lib/wireshark/extcap

ln -s $(pwd)/python_cli/sniffle_extcap.py ~/.local/lib/wireshark/extcap

```



On Mac OS, Wireshark may try to use the Xcode Python rather than the Python in your PATH specified

by your shell profile. Thus, the Sniffle plugin may fail to show up in extcap interfaces if PySerial

is not installed for the Xcode Python. To fix this, you can edit the shebang line of

`sniffle_extcap.py` to directly point to the Python with PySerial installed, for example the

Homebrew Python at `/opt/homebrew/bin/python3`, rather than `/usr/bin/env python3`.



On Windows, you can copy the following files and directories from the `python_cli` directory into

your Personal Extcap folder:



```

sniffle/

sniffle_extcap.py

sniffle_extcap.bat

```



On Windows, it may be necessary to edit `sniffle_extcap.bat` to specify the location of

the python interpreter if the installation directory is not included in the PATH, e.g.:



```

@echo off

C:\my_python_install\python.exe "%~dp0sniffle_extcap.py" %*

```



Once the plugin has been installed, restart Wireshark or choose *Capture* > *Refresh Interfaces*

to enable the Sniffle interface.



## Transmit Functionality



While the original 2019 Sniffle firmware was purely a passive listener, later firmware versions

added various features to actively transmit packets in various ways. Current Sniffle firmware

supports acting as both a GAP central and peripheral device, including active scanning, legacy

and extended advertising, initiating connections, and being connected in a master (central) or

slave (peripheral) role. The `scanner.py` script performs active scanning. The `initiator.py`

script initiates a connection to a peripheral and then acts as a connected master. The

`advertiser.py` script performs legacy advertising and accepts connection requests from other

devices, transitioning to a connected slave role.



The transmit functionality of Sniffle is a little different from a traditional HCI-based Bluetooth

controller, because it gives you very low level control of the exact PDUs being sent at the link

layer. This low-level control allows the host-side code to implement additional functionality,

such as link layer fuzz testing or link layer relay attacks.



I have not yet taken the time to formally document the Sniffle firmware's API, though it is fairly

self-explanatory when looking at its host-side implementation in `sniffle_hw.py`. Active scanning

(that transmits scan requests) is activated by `cmd_scan`. Connection initiation is triggered by

`cmd_connect`, though it's easiest to use the `initiate_conn` wrapper. Advertising (optionally

connectable) is activated by `cmd_advertise` for legacy advertising, or `cmd_advertise_ext` for

extended advertising.



## XDS110 UART Latency



At least at the time of writing, the TI XDS110 debugger included in Launchpad boards has some

undesirable behaviour in its USB to UART bridge, where at high baud rates, there can be severe

latency, especially with frequent small writes as done by the Sniffle firmware. This issue has

been present for years, and is still present as of April 2024 with the XDS110 firmware 3.0.0.28

bundled with UniFlash 8.6.0. The root cause is that in DMA based operation, the XDS110 firmware

accumulates UART data in a buffer whose size is proportional to baud rate, and waits for this

buffer to fill before transferring the data. There is logic to flush this buffer if no new data

has arrived over the last 15 milliseconds, but this flushing logic is never triggered when Sniffle

is frequently adding small packets from connection events every few milliseconds. As a result of

this suboptimal behaviour, sniffed data can appear in delayed bursts on the host.



The XDS110 firmware also has an alternate mode for UART operation, where every UART receive

triggers an interrupt that results in data immediately being passed to the host. This

interrupt-based mode of operation has much lower latency. However, the firmware only uses it for

baud rates below 230400. As a workaround to the high latency of DMA mode operation with frequent

small data chunks, you can modify the firmware to use interrupt-based USB-UART bridging even at

high baud rates (like 2M baud as used by Sniffle). In firmware 3.0.0.28 (included with Uniflash

8.6.0), you can hex edit the bytes at offset 0x0A14 from 61 3F to 00 1F. This will change the

baud rate for switching to DMA-based UART operation from 230400 to 0x200000 (2097152).



Be aware that the offsets and byte modifications described above are only for firmware 3.0.0.28,

and will be different for different firmware versions. Flashing invalid firmware onto your debugger

may damage it, and we assume no responsibility for any damage that may occur.



The following commands can be used on Linux to modify the XDS110 firmware for low latency UART

at high baud rates:



```

cd ~/ti/uniflash_8.6.0/deskdb/content/TICloudAgent/linux/ccs_base/common/uscif/xds110/

cp firmware_3.0.0.28.bin firmware_3.0.0.28_fastuart.bin

printf '\x00\x1f' | dd of=firmware_3.0.0.28_fastuart.bin bs=1 seek=$((0x0A14)) conv=notrunc

sha256sum firmware_3.0.0.28_fastuart.bin

```



Before flashing, verify that the SHA256 sum of the modified firmware is

`c226f2e9cb2b9f0bc111ca11f2903d58d4065293468623428c0e8eeb22086dcf`. After verifying this,

run the following commands to flash the modified XDS110 debugger firmware:



```

./xdsdfu -m

./xdsdfu -f firmware_3.0.0.28_fastuart.bin -r

```