Technical Specifications

M Token Specification

Low-level technical specification for the M token - function signatures, events, errors, and storage layout.

Contract overview

The MToken contract is an immutable ERC20-compliant token with a dual-balance accounting system. It implements continuous compounding for earning accounts via a global index mechanism.

Decimals: 6
Index precision: 12 decimal places (scaled by 1e12)
Inherits: ContinuousIndexing, ERC20, EIP-2612, EIP-3009

Key functions

ERC20 Standard

Function	Description
`transfer(address to, uint256 amount)`	Transfer tokens to an address
`transferFrom(address from, address to, uint256 amount)`	Transfer tokens on behalf of another address
`approve(address spender, uint256 amount)`	Approve a spender allowance
`balanceOf(address account)`	Returns current balance including accrued interest for earners
`totalSupply()`	Returns `totalEarningSupply() + totalNonEarningSupply()`

EIP-2612 Permit

Function	Description
`permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s)`	Gasless approval via signature

EIP-3009 Transfer with Authorization

Function	Description
`transferWithAuthorization(address from, address to, uint256 value, uint256 validAfter, uint256 validBefore, bytes32 nonce, uint8 v, bytes32 r, bytes32 s)`	Transfer via signed authorization
`receiveWithAuthorization(address from, address to, uint256 value, uint256 validAfter, uint256 validBefore, bytes32 nonce, uint8 v, bytes32 r, bytes32 s)`	Receive via signed authorization

Earning Management

Function	Description
`startEarning()`	Convert caller's balance to earning mode (must be approved earner)
`stopEarning()`	Convert caller's balance back to non-earning mode
`stopEarning(address account_)`	Force-stop earning for an account no longer on the approved list

Balance Queries

Function	Returns
`balanceOf(address account)`	Current balance (including accrued interest for earners)
`principalBalanceOf(address account)`	Underlying principal for earning accounts (0 for non-earners)
`isEarning(address account)`	Whether the account is in earning mode
`totalEarningSupply()`	Total tokens in earning balances (present value)
`totalNonEarningSupply()`	Total tokens in non-earning balances

Index Management

Function	Description
`updateIndex()`	Update the global earning index; called by `MinterGateway` and internally
`currentIndex()`	Returns the current index value (on-demand calculation)
`latestIndex`	Last stored index value (uint128)
`latestUpdateTimestamp`	Timestamp of last index update (uint40)

Supply Control (MinterGateway only)

Function	Description
`mint(address recipient, uint240 amount)`	Mint tokens to an address
`burn(address account, uint240 amount)`	Burn tokens from an address

Events

Event	Description
`Transfer(address indexed from, address indexed to, uint256 value)`	Standard ERC20 transfer
`Approval(address indexed owner, address indexed spender, uint256 value)`	Standard ERC20 approval
`StartedEarning(address indexed account)`	Account entered earning mode
`StoppedEarning(address indexed account)`	Account exited earning mode

Errors

Error	Condition
`NotApprovedEarner()`	Account is not on the approved earners list
`IsApprovedEarner()`	Attempted to force-stop an account that is still approved
`NotMinterGateway()`	Caller is not the `MinterGateway`
`InsufficientBalance(address account, uint256 balance, uint256 amount)`	Transfer or burn exceeds balance

Continuous compounding formula

The global index grows via continuous compounding:

\text{newIndex} = \text{oldIndex} \times e^{(\text{rate} \times \text{timeElapsed} / \text{SECONDS\_PER\_YEAR})}

The e^x function uses a Padé approximant R(4,4):

e(x) \approx \frac{1 + \frac{x}{2} + \frac{3x^2}{28} + \frac{x^3}{84} + \frac{x^4}{1680}}{1 - \frac{x}{2} + \frac{3x^2}{28} - \frac{x^3}{84} + \frac{x^4}{1680}}

Rounding rules

Operation	Rounding	Protocol favored
Start earning (present → principal)	Down	Yes
Stop earning (principal → present)	Down	Yes
Earner-to-earner transfer (sender)	Up	Yes
Non-earner-to-earner transfer (receiver)	Down	Yes
Mint to earner	Down	Yes
Burn from earner	Up	Yes

M Token overview - Full conceptual documentation
Rate Models - How interest rates are determined
Minting & Burning - Supply control via MinterGateway

M Token

Complete technical documentation for the M token, the immutable ERC20-compliant token at the heart of the M0 Ecosystem.

Minting & Burning (MinterGateway)

Complete documentation of the MinterGateway contract, the central hub for minting and burning, managing minter collateral, and tracking debt obligations.