pasm

PASM, short for Propeller Assembly, is the low‑level assembly language used to program Parallax’s Propeller microcontroller family. It is designed for precise, deterministic control of hardware and is typically used for timing-critical tasks or routines that require direct access to I/O and processor resources. PASM is often employed alongside higher‑level languages such as Spin to optimize performance where needed.

The Propeller architecture features multiple parallel processing units called cogs. Each cog can execute its own PASM code independently, while all cogs share access to hub memory. This architecture makes PASM suitable for tasks such as bit‑banging, real‑time I/O, hardware interfacing, and tight control loops, where predictable timing is essential. PASM programs are assembled with Parallax’s Propeller Tool using the pasm assembler, producing code that runs inside the selected cog.

PASM provides direct control over registers and the hardware features of the Propeller, enabling low‑level optimizations not easily achievable in higher‑level languages. It is typically used to implement performance‑critical routines that can be invoked from Spin or run as dedicated cog services. The language emphasizes deterministic instruction timing and straightforward mapping to the hardware, which makes it a common choice for real‑time drivers and hardware interfaces in Propeller projects.

In the broader context, PASM is one of the core components of the Propeller toolchain and ecosystem. It complements Spin by offering a path to maximum efficiency for time‑sensitive operations, while still benefiting from the Propeller’s parallel, multi‑core design.

See also: Parallax Propeller, Spin (programming language), Propeller Tool.