Glossary

The acronyms, in plain English. Grouped loosely; use search.

Chips and cores

MCU (microcontroller unit). A CPU with flash, RAM, and peripherals on one chip. Runs your firmware directly. SoC (system on chip). A bigger chip: application processor, GPU, memory controller, radios. Usually runs Linux. SBC (single-board computer). An SoC on a ready-made board, like a Raspberry Pi. FPGA (field-programmable gate array). Reconfigurable digital logic. You describe hardware rather than write software. Cortex-M Arm's family of microcontroller cores (M0+, M4, M7, M33, M55...). The Pico 2 and STM32s use them. RISC-V An open instruction set architecture, increasingly common in new microcontrollers. The Pico 2 has RISC-V cores too. ISA (instruction set architecture). The set of instructions a CPU understands. NVIC (nested vectored interrupt controller). The part of a Cortex-M that prioritizes and dispatches interrupts. PLL (phase-locked loop). Multiplies a slow, accurate clock into the fast one the core runs at. XIP (execute in place). Running code directly from external flash instead of copying it to RAM first.

Memory

Flash Non-volatile memory where code and constants live. Slow to write, erased in blocks. SRAM Fast volatile memory for variables, stack, and heap. Lost at power-off. EEPROM Byte-writable non-volatile memory, often emulated in flash on modern MCUs. .text / .data / .bss Linker sections: code, initialized variables, and zero-initialized variables. Memory map The table of which addresses belong to flash, RAM, and each peripheral's registers. MMIO (memory-mapped I/O). Peripherals controlled by reading and writing addresses, as if they were memory. Endianness Byte order of multi-byte values. Cortex-M is little-endian: least significant byte at the lowest address. Alignment The requirement that a value's address be a multiple of its size. Violating it is slow or a fault.

Peripherals and signals

GPIO (general-purpose input/output). A pin you control directly. Pull-up / pull-down A resistor that gives an undriven pin a default level. Push-pull / open-drain Output types: one drives high and low; the other only pulls low and relies on a pull-up. PWM (pulse-width modulation). A fast square wave whose duty cycle encodes an analog-like value. ADC / DAC Analog-to-digital and digital-to-analog converters. Timer / counter Hardware that counts clock cycles and fires events at compare values or measures input edges. Prescaler A divider that slows a clock before it reaches a timer. DMA (direct memory access). Hardware that copies data between memory and peripherals without the CPU. ISR / IRQ Interrupt service routine (the function) and interrupt request (the signal that triggers it). Watchdog A timer that resets the chip if firmware stops feeding it. RTC (real-time clock). A low-power clock that keeps time through sleep. Debounce Filtering the mechanical bounce of a switch so one press reads as one press.

Communication

UART Asynchronous serial: two wires, agreed baud rate, start and stop bits. Baud Symbols per second on a serial line; for UART, bits per second. SPI Synchronous serial with clock, data in, data out, and a chip select per device. Fast. I2C Two-wire synchronous bus with addresses and acknowledgments. Slower, fewer pins. RS-232 / RS-485 Electrical standards for serial over cables: single-ended short range, and differential long range. CAN Controller area network. A robust multi-master bus used in vehicles and machines. USB CDC / HID USB device classes for a virtual serial port and for keyboards, mice, and similar. BLE Bluetooth Low Energy. GAP and GATT are its connection and data layers. MQTT A lightweight publish/subscribe protocol for sending device data to servers. Modbus A 1979 industrial protocol still everywhere, usually over RS-485.

Software

Bare metal Firmware with no operating system; your code owns the whole chip. RTOS (real-time operating system). A small kernel providing tasks, scheduling, and synchronization with predictable timing. Superloop The simplest firmware structure: one loop that polls everything. HAL (hardware abstraction layer). Code that hides register details behind functions. BSP (board support package). Code and configuration specific to one board: which pin does what. Driver Code that operates one peripheral or external device through a defined interface. State machine Code organized as explicit states and transitions driven by events. Ring buffer A fixed-size queue that wraps around. Under every UART driver. Mutex / semaphore Synchronization primitives: one protects a shared resource; the other signals events or counts resources. Priority inversion A high-priority task waiting on a low-priority one that has been preempted by a medium one. Bootloader Small firmware that runs first and can install or verify the main application. DFU / OTA Device firmware update, and over-the-air update via a radio. Linker script Tells the linker where each section goes in memory. Vector table The table of handler addresses the CPU reads at reset and on each interrupt. Cross-compilation Building on one machine (your laptop) for another (the MCU). Toolchain Compiler, assembler, linker, and binary utilities for a target, e.g. arm-none-eabi-gcc. CI (continuous integration). Automatically building and testing on every push. MISRA C Coding guidelines for safety-critical C. BARR-C is a lighter, free alternative. Static analysis Finding bugs by examining code without running it. Device tree A data structure describing hardware to the Linux kernel or Zephyr.

Debugging and measurement

SWD / JTAG Debug ports: Arm's two-wire serial wire debug, and the older, wider standard. Debug probe The adapter between your computer and the chip's debug port (ST-LINK, Raspberry Pi Debug Probe, J-Link). GDB / OpenOCD The debugger, and a common bridge between it and a probe. HardFault A Cortex-M exception raised when something is seriously wrong: bad address, bad instruction, bus error. Logic analyzer Captures digital signals over time and decodes protocols. Oscilloscope Shows voltage over time, including the analog truth a logic analyzer hides. DMM Digital multimeter. Burden voltage The voltage a multimeter drops when measuring current, which can starve the device under test. Power profiler An instrument that measures current across many decades at high speed (Otii Arc, PPK2).

Power and robustness

Sleep / Stop / Standby Progressively deeper low-power modes with progressively more turned off. Tickless An RTOS mode that stops the periodic tick so the chip can sleep between events. Brown-out A supply voltage dip low enough to make the chip misbehave; a BOR detector resets it first. ESD Electrostatic discharge, tested per IEC 61000-4-2. EMI / EMC Electromagnetic interference and compatibility: not disturbing others and not being disturbed. EFT Electrical fast transients (burst), tested per IEC 61000-4-4. Surge A high-energy pulse from lightning or switching, tested per IEC 61000-4-5. TVS diode A component that clamps voltage spikes to protect a circuit. CRC (cyclic redundancy check). A checksum that detects corrupted data.

Safety and security

Functional safety Engineering so that failures do not cause harm. IEC 61508 (general) and ISO 26262 (automotive) are the standards. SIL / ASIL Safety integrity levels: how bad a failure could be, and therefore how rigorous development must be. FMEA Failure modes and effects analysis: systematically asking "what if this fails?" Secure boot / chain of trust Each stage verifies the next before running it, starting from immutable ROM. Code signing A digital signature on a firmware image so the device can verify its origin. TrustZone-M Arm hardware that splits a Cortex-M into secure and non-secure worlds. PSA Certified A security framework and certification scheme for IoT devices. Threat model A written analysis of what you protect, from whom, and how. RDP Readout protection: locking the debug port so flash cannot be read.