Architecture

XCellMain​

XCellMain upgradable contract (aka XCellMatic for MATIC or XCellGraph for GRT) is the core contract that acts as a liquid staking pool aggregator. It is responsible for token deposits, minting and burning liquid staking tokens (xcTokens), staking/unstaking funds to the validating nodes and applying fees.

On a regular basis an off-chain service calls the public method autobalance triggering the staking of funds into the validating nodes. Any contract or user can call this method.

Exchange Rate​

The exchange rate of the underlying token to xcToken (e.g. MATIC to xcMATIC) is calculated as the total amount of tokens (deposits + rewards) divided by the supply of xcTokens. The value of the xcToken will increase over time with respect to the base token.

On some chains, where slashing is enabled, a particular validator may be penalized due to missing validation checkpoints or misbehaviour, and thus a portion of the staked funds on that given validator is slashed. This will in turn cause the exchange rate to decrease.

Rewards​

As the staking rewards are distributed to the validators, XCell will account for such rewards, while a percentage will be transferred to the XCell treasury in accordance to the current fees.

Flash Exit & Liquidity Pool​

As part of the staking process, the contract will reserve a portion of the funds to act as a liquidity pool, thus enabling the feature "Flash Exit". During a Flash Exit transaction, no unstaking from the validating nodes takes place, instead funds come directly from the contract's token balance.

Nodes​

Nodes are pre-approved by XCell as trusted validators. Their selection is based on their performance record validating transactions, their fees and their SLA.

xcToken​

xcToken is a standard non-upgradable ERC20 token. At deployment time, ownership is set to XCellMain, and thus XCellMain is the only contract or entity allowed to mint and burn xcTokens.

RoleManager​

The protocol implements Openzeppelin's AccessControl contract to determine roles and limit access on methods to XCellMain. The roles implemented are:

• TIMELOCK_UPGRADES_ROLE: Role to upgrade XCellMain through a TimeLock contract

• TIMELOCK_ROLE: Role to execute XCellMain operations functions through a TimeLock contract

• XC_SERVICE_ROLE: Role to execute daily operations on XCellMain without the need of TimeLock

TimeLock​

Implements Openzeppelin's TimelockController to introduce time delay on some given functions in XCellMain.