The Maize Instruction Set Architecture, Version 1.0

This directory is the normative specification of the Maize virtual machine's instruction set architecture (ISA). Version 1.0 is the behavioral freeze point: the register model, the instruction encoding, every instruction's operation and flag effects, the memory model, the trap model, the device-facing surface, and the floating-point contract are fixed here and do not change within the v1.x series except by the additive, reserved-space rules of Chapter 12 and Chapter 15.

Freeze status

v1.0 freezes behavior, not timing. Every observable result of every instruction is pinned. The cycle-cost / performance model is specified separately (Chapter 14 is a pointer to it) and is explicitly out of the behavioral freeze. Conformance (Chapter 13) is defined against behavior alone.

How to read this specification

Each chapter is a single Markdown file. This index assigns the chapter numbers and the reading order; the chapter files themselves are the normative text. The three chapters marked EXISTS are incorporated by reference: their files are canonical and are not restated here.

Normative vs informative. Unless a passage is explicitly marked informative (or sits under a heading named "Rationale", "Note", or "Positioning"), it is normative: a conforming implementation must behave as it says. Informative passages explain intent and never add a requirement.

The reference implementation is normative ground truth. Maize is spec-as-product: the reference VM (src/cpu.cpp, src/maize_cpu.h) is the definition of correct behavior, and every normative claim in these chapters is grounded in the shipped dispatch, with the repository README.md opcode and flag tables as the human-readable cross-check. Where a chapter states what the machine does, it states what the code does. Each newly authored chapter carries a Sourcing section naming the code and tables its claims are keyed to.

No undefined behavior. Every condition that is undefined behavior on a conventional machine is, on Maize, either a named trap (Chapter 10) or an explicitly enumerated defined, non-trapping result. There is no third category. This is the single property that makes the machine conformance-testable and two conforming VMs bit-for-bit equivalent on every input.

Notation

Numeric radix prefixes, used throughout Maize source and documentation:

• % precedes a binary value: %0100_0001.
• # precedes a decimal value: #123.
• $ precedes a hexadecimal value: $FEDC.

The separators ` (back-tick), _ (underscore), and , (comma) are all legal inside any numeric literal and carry no value; group digits however reads best ($FEDC`BA98, %0100_0001, #1,000,000). A bare token with no prefix is decimal. An operand written with a leading @ is a memory address that gets dereferenced; without @ it is a plain value (Chapter 5).

Table of contents

What v1.0 is, in one paragraph

Maize is a flat 64-bit CISC byte-code machine with sixteen operand-addressable 64-bit registers, each sliced into byte / quarter-word / half-word / word subregisters; variable-length instructions built from a one-byte opcode (two mode bits plus a six-bit base slot) and one operand byte per operand; a sparse, no-fault, little-endian memory; five arithmetic/logic flags (C, N, V, P, Z) plus four privileged status bits; a precise, fully-defined trap model; a Zfinx floating-point extension (IEEE-754 binary32 and binary64 in the integer registers with a separate FCSR); a port-mapped device surface with no MMIO; and a reserved-space schedule that lets paging, segments, atomics, and SMP arrive later without breaking a single v1.0 binary.