Interview

Process

A running program with its own separate memory space.

Thread

A smaller unit of execution inside a process; threads share memory.

Process vs thread

Processes have separate memory; threads share memory and are lighter weight.

Race condition

A bug where output depends on timing/order of shared resource access.

Mutex

A lock that allows one thread at a time into a critical section.

Semaphore

A synchronization tool that controls access to a limited number of resources.

Deadlock

When threads/processes wait forever for resources held by each other.

Critical section

Code that accesses shared data and must be protected from simultaneous access.

Synchronous operation

The caller waits for the operation to finish before continuing.

Asynchronous operation

The operation can run without blocking the caller until completion.

Blocking call

A call that waits until the operation finishes.

Non-blocking call

A call that returns immediately even if the operation is not complete.

Polling

Repeatedly checking whether an event has happened.

Interrupt

A signal that notifies the CPU/system that an event needs attention.

Polling vs interrupt

Polling repeatedly checks; interrupts notify only when something happens.

TCP

Reliable, ordered, connection-based communication with retransmission.

UDP

Fast, connectionless, best-effort communication without delivery guarantees.

TCP vs UDP

TCP prioritizes reliability/order; UDP prioritizes low latency/simplicity.

Why UDP for telemetry

Fresh real-time data is usually more useful than delayed retransmitted old data.

When to use TCP

Commands, configuration, file transfer, software updates, or anything requiring reliable delivery.

When to use UDP

High-rate telemetry, video, audio, broadcasts, or data where occasional loss is acceptable.

IP address

Identifies a device or network interface on a network.

Port

Identifies a specific service/application on a device.

Socket

A communication endpoint, usually IP address plus port plus protocol.

Client

The side that initiates a request or connection.

Server

The side that listens for requests or connections.

Network interface

A network adapter/connection such as Ethernet, Wi-Fi, USB Ethernet, loopback, VPN, or virtual adapter.

Subnet

A logical network range where devices can often communicate directly.

Gateway

The device traffic goes through to reach other networks.

ping

Command used to test whether another device is reachable.

ip addr

Linux command used to view network interfaces and IP addresses.

ip route

Linux command used to view where network traffic will be sent.

ss -tulnp

Linux command used to show listening TCP/UDP ports and owning processes.

netstat

Older command used to inspect network connections and listening ports.

nc / netcat

Tool used to test whether a port is reachable or send simple network data.

tcpdump

Command-line tool for capturing and inspecting network packets.

Wireshark

GUI tool for capturing and analyzing network packets.

Firewall

Software/hardware that can block traffic by IP, port, or protocol.

Port not open

Common causes: service not running, wrong interface, wrong port, or firewall blocking it.

Network unreachable

Common causes: wrong IP, bad subnet, missing route, cable issue, or wrong interface.

Embedded Linux

Linux running on dedicated hardware or embedded devices.

ps

Command used to show running processes.

top

Command used to view live CPU/memory/process usage.

kill

Command used to terminate a process by PID.

systemctl status

Command used to check the status of a Linux service.

journalctl

Command used to view systemd logs.

journalctl -u service

Command used to view logs for a specific service.

tail -f

Command used to follow a log file live.

dmesg

Command used to view kernel/device messages.

lsusb

Command used to list USB devices detected by Linux.

lspci

Command used to list PCI devices detected by Linux.

/dev

Linux directory where device files appear.

/dev/ttyUSB0

Common device path for a USB serial adapter.

/dev/ttyS0

Common device path for a built-in serial port.

chmod +x

Makes a script executable.

rwx permissions

Read, write, execute permissions on Linux files.

UART

Asynchronous serial communication using TX/RX and start/stop bits.

SPI

Synchronous serial protocol using clock, MOSI, MISO, and chip select.

I2C

Synchronous two-wire protocol using clock/data and device addresses.

CAN bus

Robust message-based bus commonly used in vehicles and embedded systems.

Synchronous serial

Sender and receiver share a clock signal; examples include SPI and I2C.

Asynchronous serial

No shared clock; data uses start/stop bits; example is UART.

UART vs SPI

UART is asynchronous TX/RX; SPI is synchronous, usually faster, and uses clock/chip select.

SPI vs I2C

SPI is faster with more wires; I2C uses two wires and addressed devices.

ADC

Analog-to-digital converter; converts analog voltage into a digital value.

DAC

Digital-to-analog converter; converts digital values into analog voltage.

GPIB

Older lab instrument communication bus.

VISA

Software API/layer commonly used to communicate with lab instruments.

Modbus

Industrial communication protocol used for devices/controllers.

VLAN

Virtual LAN used to logically separate network traffic.

HITL / HIL

Hardware-in-the-loop; testing real hardware with simulated inputs/environment.

Virtualized hardware simulation

Test environment that simulates hardware behavior without the physical device.

Test stand

A hardware/software/instrumentation setup used to run tests.

Test fixture

Physical or electrical setup that holds/connects hardware under test.

Instrumentation

Measurement/control equipment such as scopes, power supplies, sensors, or analyzers.

Acceptance criteria

The conditions a component or test must meet to be considered passing.

Flaky test

A test that sometimes passes and sometimes fails without a clear product change.

Common flaky test causes

Timing issues, race conditions, environment state, weak waits, hardware setup issues, or network instability.

Root cause analysis

Finding the underlying reason a failure happened, not just the symptom.

Regression

A bug that reappears or a feature that breaks after a change.

CI / Continuous Integration

Automatically building and testing code after changes.

Jenkins

CI tool used to run builds, tests, scripts, and deployment steps.

Unit test

Test of a small isolated piece of code.

Integration test

Test that checks multiple components working together.

System test

Test of full system behavior.

End-to-end test

Test that exercises a full workflow like a real user/system.

Code coverage

Metric showing how much code is executed by tests.

Coverage threshold

Minimum required code coverage level before a build can pass.