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Savings crvUSD

Savings crvUSD, in short scrvUSD, is a savings version of crvUSD.

Smart Contracts

  • VaultV3.vy

    The Vault contract is based on Yearn's VaultV3.vy contract, more precisely version 3.0.4. It is an ERC4626 compliant Vault that handles all logic associated with deposits, withdrawals, strategy management, profit reporting, etc.

    Yearn Dev Docs

  • RewardsHandler.vy

    The RewardsHandler is a peripheral contract that implements the weight function needed by the FeeSplitter. This function enables the Vault to receive rewards to depositors based on the proportion of crvUSD deposited in the Vault.

    Read more

  • StablecoinLens.vy

    Helper contract to calculate the circulating supply of crvUSD by excluding e.g. pre-minted crvUSD for flashloans.

    Read more

The documentation of the FeeSplitter contract can be found here.

Vault Implementation Details

The Vault is an unmodified instance of the Yearn V3 multi-strategy Vault that accepts crvUSD deposits. The crvUSD deposited into the Vault are not rehypothecated, they sit idle in the Vault to earn yield.

This Vault aims to be as cheap as possible for users to deposit and withdraw funds. For this reason funds deposited in the Vault are not moved anywhere and are always available to be redeemed.

Although the Vault is called "multi-strategy" it actually doesn't contain any strategies. This is possible thanks to yearn Vaults' v3.0.3 ability to report on self.

Rewards

The Vault receives a dynamic percentage of the interest fees generated by the crvUSD from the FeeSplitter contract which is then distributed linearly across all depositors with respect to their share of the total deposits. Inbetween the FeeSplitter and the Vault, there is a RewardsHandler contract that handles the calculation of the dynamic percentage, which is determined by the ratio of crvUSD deposited into the Vault over the total circulating supply of crvUSD.

FeeSplitter Interaction and Weight Calculation

For the FeeSplitter to send funds to the RewardsHandler, the RewardsHandler must be added as a receiver in the FeeSplitter by the DAO. Once this condition is met, the FeeSplitter will send funds to the RewardsHandler according to what the weight function in the RewardsHandler returns (this value is dynamic).

The take_snapshot function allows anyone to take snapshots of the ratio of crvUSD in the Vault compared to the circulating supply of crvUSD. This ratio is used to determine the percentage of the fees that can be requested by the FeeSplitter.

For instance if the time-weighed average of the ratio is 0.1 (10% of the circulating supply is deposited into the Vault), the FeeSplitter will request 10% of the fees generated by the crvUSD controllers.

Rewards Allocation

Rewards allocated to scrvUSD come from crvUSD interest fees or any external donations sent to the RewardsHandler contract.

The ultimate amount of rewards is dynamic and is determined by the ratio of the staked supply to the total supply of crvUSD. Although it is dynamic, the weight has an upper and lower bound.

Rewards are distributed to scrvUSD holders thought the RewardsHandler contract using a simple process_rewards function. This function permnissionlessly lets anyone distribute rewards to the crvUSD Vault.

Although the weight is dynamic, it has a upper and lower bound:

  1. The lower bound is defined in the RewardsHandler contract as minimum_weight. This is the minimum percentage of rewards that scrvUSD will receive.
  2. The upper bound is defined in the FeeSplitter and represents the maximum percentage of rewards that scrvUSD will receive from the FeeSplitter. The FeeSplitter allows for dynamic weights, which is the case for scrvUSD. This upper value can be checked in the FeeSplitter contract by calling FeeSplitter.receivers(i), where i is the index of the receiver. This method returns the address and the maximum weight of the receiver.