Inline Assembler for Thumb2 architectures

(The Technic Hub uses an ARM Cortex-M4 processor which uses Thumb2 instructions, so this section of the Micropython docs has been left in, but it’s left as an exercise for the reader how to actually get started doing assembler programming on the Hub!)

This document assumes some familiarity with assembly language programming and should be read after studying a Thumb2 tutorial like the Pyboard Assembler Tutorial in the main Micropython docs. For a detailed description of the instruction set consult the Architecture Reference Manual detailed below. The inline assembler supports a subset of the ARM Thumb-2 instruction set described here. The syntax tries to be as close as possible to that defined in the above ARM manual, converted to Python function calls.

Instructions operate on 32 bit signed integer data except where stated otherwise. Most supported instructions operate on registers R0-R7 only: where R8-R15 are supported this is stated. Registers R8-R12 must be restored to their initial value before return from a function. Registers R13-R15 constitute the Link Register, Stack Pointer and Program Counter respectively.

Document conventions

Where possible the behaviour of each instruction is described in Python, for example

  • add(Rd, Rn, Rm) Rd = Rn + Rm

This enables the effect of instructions to be demonstrated in Python. In certain case this is impossible because Python doesn’t support concepts such as indirection. The pseudocode employed in such cases is described on the relevant page.

Usage examples

These sections provide further code examples and hints on the use of the assembler.

References