ppsspp-dfx

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ppsspp_write_register

Destructive

Set a PSP CPU register (GPR/FPU/VFPU, pc/hi/lo) to a hex value during PPSSPP debugging; automatically pauses and resumes the emulator.

Instructions

PURPOSE: Set a CPU register (GPR/FPU/VFPU names, plus pc/hi/lo).

USAGE: session_id + name (MIPS ABI names preferred; numeric aliases like 'r5' normalize to the GPR of that index, i.e. r5 -> a1) + value (hex).

BEHAVIOR: DESTRUCTIVE. Pauses and resumes the CPU automatically (REQUIRED_STEPPING handled internally) — no manual pause needed.

RETURNS: {name, value, response, text}.

Input Schema

TableJSON Schema

Name	Required	Description
`name`	Yes	CPU register name (MIPS standard names). GPRs: 'v0'/'v1'/'a0'-'a3'/'t0'-'t9'/'s0'-'s7'/'gp'/'sp'/'fp'/'ra'/'hi'/'lo'/'pc'. FPU: 'f0'-'f31'. VFPU: 'v0'-'v127'. Numeric aliases like 'r5' are accepted and normalized (r5 -> a1, i.e. GPR index 5) — prefer the MIPS standard name. Case-sensitive (lowercase by convention).
`value`	Yes	Value to write, as a hex string (e.g. '0x00000001'). Treated as an unsigned 32-bit int; values outside [0, 0xFFFFFFFF] are REJECTED (out-of-32-bit-range error), not wrapped.
`session_id`	Yes	Active session ID.

Output Schema

TableJSON Schema

Name	Required	Description
`name`	Yes	Register name (e.g., 'v0', 'a0', 'pc', 'hi', 'lo').
`text`	Yes	Unified text representation: 'Wrote 0x{VAL:X} → {REG}'.
`value`	Yes	Value written, hex string (e.g. '0x00000001').
`response`	Yes	Raw PPSSPP WebSocket response (may be empty).

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv0.1.6Oct 4, 2026

changedInput schema / properties / name / description

Previous value: -"CPU register name (MIPS standard names). GPRs: 'v0'/'v1'/'a0'-'a3'/'t0'-'t9'/'s0'-'s7'/'gp'/'sp'/'fp'/'ra'/'hi'/'lo'/'pc'. FPU: 'f0'-'f31'. VFPU: 'v0'-'v127'. Numeric aliases like 'r5' are NOT accepted by PPSSPP — use the MIPS standard name (e.g., 'a1' instead of 'r5'). Case-sensitive (lowercase by convention)."New value: +"CPU register name (MIPS standard names). GPRs: 'v0'/'v1'/'a0'-'a3'/'t0'-'t9'/'s0'-'s7'/'gp'/'sp'/'fp'/'ra'/'hi'/'lo'/'pc'. FPU: 'f0'-'f31'. VFPU: 'v0'-'v127'. Numeric aliases like 'r5' are accepted and normalized (r5 -> a1, i.e. GPR index 5) — prefer the MIPS standard name. Case-sensitive (lowercase by convention)."

changedInput schema / properties / value / description

Previous value: -"Value to write, as a hex string (e.g. '0x00000001'). Treated as an unsigned 32-bit int; values outside [0, 0xFFFFFFFF] are wrapped by PPSSPP."New value: +"Value to write, as a hex string (e.g. '0x00000001'). Treated as an unsigned 32-bit int; values outside [0, 0xFFFFFFFF] are REJECTED (out-of-32-bit-range error), not wrapped."

First observedv0.1.0Sep 16, 2026

TDQS

A3.9/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare destructiveHint=true and readOnlyHint=false, so the safety profile is covered. The description adds genuine value beyond them by disclosing that the CPU is paused and resumed internally and that no manual pause is required.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The PURPOSE/USAGE/BEHAVIOR/RETURNS structure is front-loaded and easy to scan. The USAGE line slightly duplicates schema information, but no sentence is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, the RETURNS line is a bonus rather than a necessity, and the pause/resume disclosure closes the main behavioral gap. Complete enough for a destructive mutation tool whose annotations already carry the safety signals.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, and the name/value descriptions already document alias normalization, hex format, and out-of-range rejection. The description largely echoes the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a precise verb (Set) plus resource (CPU register) and enumerates scope: GPR/FPU/VFPU names plus pc/hi/lo. This is enough to distinguish it from the sibling ppsspp_write_memory without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The USAGE line only restates the required parameter trio already declared in the schema and adds no when-to-use or when-not guidance. It never says when to prefer this over ppsspp_write_memory or other mutation tools, so usage is only implied.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.