---
title: "Alloy"
canonical_url: https://developer.repebble.com/docs/c/Foundation/Alloy/
last_updated: 2026-11-09
sdk_version: 4.44
---
# Alloy

Source: https://developer.repebble.com/docs/c/Foundation/Alloy/

The APIs on this page will only work with SDK 4.9+.

## Function Documentation

void moddable\_createMachine([ModdableCreationRecord](https://developer.repebble.com/docs/c/Foundation/Alloy.md#ModdableCreationRecord) \* creation)

Create and start a Moddable XS virtual machine for an Alloy app.

#### Parameters
 creation

Configuration record, or NULL for default settings.

#### See Also
[ModdableCreationRecord](https://developer.repebble.com/docs/c/Foundation/Alloy.md#ModdableCreationRecord)

## Data Structure Documentation

struct ModdableCreationRecord

Configuration record for creating a Moddable XS virtual machine. Used with [moddable\_createMachine()](https://developer.repebble.com/docs/c/Foundation/Alloy.md#moddable_createMachine) to customize the JS runtime. Set recordSize to sizeof(ModdableCreationRecord) for version compatibility.

#### Data Fields
[uint32\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint32_t) recordSize

Size of this struct in bytes (for versioning)

[uint32\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint32_t) stack

Stack size in bytes (0 for default)

[uint32\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint32_t) slot

Slot heap size in bytes (0 for default)

[uint32\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint32_t) chunk

Chunk heap size in bytes (0 for default)

[uint32\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint32_t) flags

Combination of kModdableCreationFlag\* values.

void \* fxBuildFFI

Optional pointer to an fxBuildFFI function for custom native bindings.

## Macro Definition Documentation

#define kModdableCreationFlagLogInstrumentation (1 \<\< 0)

Flag to enable XS instrumentation logging over Bluetooth. When set, the Moddable XS engine will log instrumentation data (e.g. memory usage, slot/chunk/stack statistics) via app\_log. Logging is only active when a Bluetooth log listener is connected; otherwise this flag has no effect.

#### See Also
[ModdableCreationRecord](https://developer.repebble.com/docs/c/Foundation/Alloy.md#ModdableCreationRecord)

#define kModdableCreationFlagDebug (1 \<\< 1)

Flag to enable XS debugging using xsbug. Should be used in combination with pebble build -debug.

#### See Also
[ModdableCreationRecord](https://developer.repebble.com/docs/c/Foundation/Alloy.md#ModdableCreationRecord)