Parallax Propeller - Built in SPIN Byte Code Interpreter

Built in SPIN Byte Code Interpreter

Spin is a multitasking high level computer programming language created by Parallax's Chip Gracey, who also designed the Propeller microcontroller on which it runs, for their line of Propeller microcontrollers.

Spin code is written on the Propeller Tool, a GUI oriented software development platform written for Windows XP. This compiler converts the Spin code into bytecodes that can be loaded (with the same tool) into the main 32 KB RAM, and optionally into the serial boot FLASH EEPROM, of the Propeller chip. After booting the propeller a bytecode interpreter is copied from the built in ROM into the 2 KB RAM of the primary COG. This COG will then start interpreting the bytecodes in the main 32 KB RAM. More than one copy of the bytecode interpreter can run in other COGs, so several Spin code threads can run simultaneously. Within a Spin code program, assembler code program(s) can be "inline" inserted. These assembler program(s) will then run on their own COGs.

Like Python, Spin uses indentation/whitespace, rather than curly braces or keywords, to delimit blocks.

The Propeller's interpreter for its proprietary multi-threaded SPIN computer language is a byte code interpreter. This interpreter decodes strings of instructions, one instruction per byte, from user code which has been edited, compiled, and loaded onto the Propeller from within a purpose-specific IDE. This IDE, which Parallax simply calls "The Propeller tool", is intended for use under the Windows operating system.

The SPIN language is a high level language. Because it is interpreted in software, it runs slower than pure Propeller assembly but can be more space-efficient (Propeller assembly opcodes are 32 bits long; SPIN directives are 8 bits long, which may be followed by a number of 8-bit bytes to specify how that directive operates). SPIN also allows users to avoid significant memory segmentation issues that must be considered for assembly code.

At startup, a copy of the byte code interpreter (less than 2 KB in size), will be copied into the dedicated RAM of a cog and will then start interpreting byte code in the main 32 KB RAM. Additional cogs can be started from that point, loading a separate copy of the interpreter into the new cog's dedicated RAM (a total of eight interpreter threads can, therefore, run simultaneously). Notably, this means that at least a minimal amount of startup code must be SPIN code, for all Propeller applications.