PySerial Driver

jumpstarter-driver-pyserial provides functionality for serial port communication.

Installation

:substitutions:
$ pip3 install --extra-index-url {{index_url}} jumpstarter-driver-pyserial

Configuration

Example configuration:

export:
  serial:
    type: jumpstarter_driver_pyserial.driver.PySerial
    config:
      url: "/dev/ttyUSB0"
      baudrate: 115200
      cps: 10  # Optional: throttle to 10 characters per second

Example configuration to send commands to a MCU with DTR/RTS controlling boot process over serial port, with --no-output (fire-and-forget mode):

export:
  serial:
    type: jumpstarter_driver_pyserial.driver.PySerial
    config:
      url: "/dev/ttyUSB0"
      baudrate: 115200
      disable_hupcl: true # Prevents MCU reset on each command/close.
      #cps: Avoid using cps when using --no-output.

Config parameters

Parameter	Description	Type	Required	Default
url	The serial port to connect to, in pyserial format	str	yes
baudrate	The baudrate to use for the serial connection	int	no	115200
check_present	Check if the serial port exists during exporter initialization, disable if you are connecting to a dynamically created port (i.e. USB from your DUT)	bool	no	True
cps	Characters per second throttling limit. When set, data transmission will be throttled to simulate slow typing. Useful for devices that can't handle fast input	float	no	None
disable_hupcl	Disable HUPCL on POSIX systems to avoid toggling DTR/RTS on close (can prevent MCU reset on serial disconnect)	bool	no	False

NVDemuxSerial Driver

The NVDemuxSerial driver provides serial access to NVIDIA Tegra demultiplexed UART channels using the nv_tcu_demuxer tool. It automatically handles device reconnection when the target device restarts.

The nv_tcu_demuxer tool can be obtained from the NVIDIA Jetson BSP, at this path: Linux_for_Tegra/tools/demuxer/nv_tcu_demuxer.

Multi-Instance Support

Multiple driver instances can share a single demuxer process by specifying different target channels. This allows simultaneous access to multiple UART channels (CCPLEX, BPMP, SCE, etc.) from the same physical device.

Configuration

Single channel example:

export:
  ccplex:
    type: jumpstarter_driver_pyserial.nvdemux.driver.NVDemuxSerial
    config:
      demuxer_path: "/opt/nvidia/nv_tcu_demuxer"
      # device defaults to auto-detect NVIDIA Tegra On-Platform Operator
      # chip defaults to T264 (Thor), use T234 for Orin

Multiple channels example:

export:
  ccplex:
    type: jumpstarter_driver_pyserial.nvdemux.driver.NVDemuxSerial
    config:
      demuxer_path: "/opt/nvidia/nv_tcu_demuxer"
      target: "CCPLEX: 0"
      chip: "T264"

  bpmp:
    type: jumpstarter_driver_pyserial.nvdemux.driver.NVDemuxSerial
    config:
      demuxer_path: "/opt/nvidia/nv_tcu_demuxer"
      target: "BPMP: 1"
      chip: "T264"

  sce:
    type: jumpstarter_driver_pyserial.nvdemux.driver.NVDemuxSerial
    config:
      demuxer_path: "/opt/nvidia/nv_tcu_demuxer"
      target: "SCE: 2"
      chip: "T264"

Config parameters

Parameter	Description	Type	Required	Default
demuxer_path	Path to the nv_tcu_demuxer binary	str	yes
device	Device path or glob pattern for auto-detection	str	no	/dev/serial/by-id/usb-NVIDIA_Tegra_On-Platform_Operator_*-if01
target	Target channel to extract from demuxer output	str	no	CCPLEX: 0
chip	Chip type for demuxer (T234 for Orin, T264 for Thor)	str	no	T264
baudrate	Baud rate for the serial connection	int	no	115200
cps	Characters per second throttling limit	float	no	None
timeout	Timeout in seconds waiting for demuxer to detect pts	float	no	10.0
poll_interval	Interval in seconds to poll for device reappearance after disconnect	float	no	1.0

Device Auto-Detection

The device parameter supports glob patterns for automatic device discovery:

# Auto-detect any NVIDIA Tegra On-Platform Operator device (default)
device: "/dev/serial/by-id/usb-NVIDIA_Tegra_On-Platform_Operator_*-if01"

# Specific serial number
device: "/dev/serial/by-id/usb-NVIDIA_Tegra_On-Platform_Operator_ABC123-if01"

# Direct device path (no glob)
device: "/dev/ttyUSB0"

Auto-Recovery

When the target device restarts (e.g., power cycle), the serial device disappears and the demuxer exits. The driver automatically:

1. Detects the device disconnection
2. Polls for the device to reappear
3. Restarts the demuxer with the new device
4. Discovers the new pts path (which changes on each restart)

Active connections will receive errors when the device disconnects. Clients should reconnect, and the driver will wait for the device to be available again.

Configuration Validation / Limitations

When using multiple driver instances, all instances must have compatible configurations:

• demuxer_path: Must be identical across all instances
• device: Must be identical across all instances
• chip: Must be identical across all instances
• target: Must be unique for each instance (no duplicates allowed)

If these requirements are not met, the driver will raise a ValueError during initialization.

Usage

The pyserial driver provides two CLI commands for interacting with serial ports:

start_console

Start an interactive serial console with direct terminal access.

j serial start-console

Exit the console by pressing CTRL+B three times.

pipe

Pipe serial port data to stdout or a file. Automatically detects if stdin is piped and enables bidirectional mode.

When stdin is used, commands are sent until EOF, then continues monitoring serial output until Ctrl+C.

Use --no-output for fire-and-forget mode: send stdin to serial and exit at EOF without reading serial output.

# Log serial output to stdout
j serial pipe

# Log serial output to a file
j serial pipe -o serial.log

# Send command to serial, then continue monitoring output
echo "hello" | j serial pipe

# Send commands from file, then continue monitoring output
cat commands.txt | j serial pipe -o serial.log

# Force bidirectional mode (interactive)
j serial pipe -i

# Append to log file instead of overwriting
j serial pipe -o serial.log -a

# Disable stdin input even when piped
cat data.txt | j serial pipe --no-input

# Fire-and-forget: send stdin to serial and exit at EOF (no serial output)
cat commands.txt | j serial pipe --no-output

Options

• -o, --output FILE: Write serial output to a file instead of stdout
• -i, --input: Force enable stdin to serial port (auto-detected if piped)
• --no-input: Disable stdin to serial port, even if stdin is piped
• -a, --append: Append to output file instead of overwriting
• --no-output: Disable serial output handling (stdin -> serial only, exits at EOF)

Notes:

• --no-output cannot be combined with --output or --append.
• --no-output requires stdin input (piped stdin or --input).

Exit with Ctrl+C.

API Reference

.. autoclass:: jumpstarter_driver_pyserial.client.PySerialClient()
    :members: pexpect, open, stream, open_stream, close

Examples

Using expect with a context manager

with pyserialclient.pexpect() as session:
    session.sendline("Hello, world!")
    session.expect("Hello, world!")

Using expect without a context manager

session = pyserialclient.open()
session.sendline("Hello, world!")
session.expect("Hello, world!")
pyserialclient.close()

Using a simple BlockingStream with a context manager

with pyserialclient.stream() as stream:
    stream.send(b"Hello, world!")
    data = stream.receive()

Using a simple BlockingStream without a context manager

stream = pyserialclient.open_stream()
stream.send(b"Hello, world!")
data = stream.receive()

from jumpstarter_driver_pyserial.driver import PySerial
from jumpstarter.common.utils import serve

instance = serve(PySerial(url="loop://"))

pyserialclient = instance.__enter__()

instance.__exit__(None, None, None)