USDs is a stablecoin which generates auto-yield natively. Currently, USDs is live on Arbitrum, the largest Layer-2 Ecosystem of Ethereum. It has achieved $20M TVL in the first 2 months since launch. Eventually, Sperax will build a system of interoperability so that USDs will be natively deployed to all major blockchain platforms.

The highlights of this protocol:

1. Auto-yield - Users holding USDs in their wallets automatically earn organic yield. No staking is required by the end user. Users do not need to spend gas calling the smart contract to claim their yield.

2. Layer 2 native — Cheaper transaction fees on Arbitrum make this protocol retail investor-friendly

3. Fully Backed Model - USDs is 100% backed by a diversified basket of whitelisted crypto assets (stablecoins)

The growth of the decentralized finance (DeFi) space has spearheaded the adoption of stablecoins. However, existing stablecoins like fiat-backed stablecoins (USDT, USDC) are centralized, CDP based stablecoins (DAI) have a difficult time scaling and algo-stablecoins (like Basis, Terra) only maintain stability during bull markets. USDs has combined the best of existing stablecoin designs by featuring a 100% backed model like the CDP stablecoins, but adds the scalability benefits of fiat backed stablecoins. An on-chain, redemption based design makes USDs highly scalable, trustless and decentralized.

USDs automates the process of earning yield on stablecoins. Yield is generated organically by sending collateral to audited decentralized finance protocols. 50% of yield generated on collateral is used to pay USDs holders Auto-Yield. USDs Auto-yield rate is adjustable and depends on the actual yield generated by the collaterals. Any yield generated beyond the max Auto-yield rate will be stored in Auto-yield reserves. This novel passive income strategy does not require any action from the user. Users can just hold USDs and see wallet balance grow, auto-compounding the yield in the process.

SPA is the governance and value accrual token of the Sperax ecosystem. SPA holders can stake SPA tokens to receive veSPA. veSPA holders are decision makers of the protocol. They will earn staking rewards and manage the protocol revenue via voting power in Sperax governance. Off-chain governance is live and community (veSPA holders) can control parameters of USDs protocol, yield strategies, eligible collateral, new product features, etc. On-chain governance will be launched soon making veSPA holders true owners of the Sperax ecosystem.

Minting USDs

To mint new USDs, minters only need eligible collateral. Currently, the protocol is accepting USDC.e, USDC, USDC.e, Frax, DAI, USDT and LUSD as collateral and more tokens might be added to this list in the future. However, USDs tokens are fungible and redeemable in the same way, independent of their underlying minting collateral. It acts as an IOU on the pooled collateral.

The protocol will mint 1 USDs by collecting 1 USD worth of collateral.

Collateral tokens required = No. of USDs tokens minted/Min (Price of collateral in USD, 1 USD)

When a collateral token is worth less than 1 dollar, it will be treated with its actual market price. However, when it is worth more than 1 dollar, it will be treated as 1 dollar. Hence, USDs will always be fully collateralized or over-collateralized.

Mint fees are subject to Sperax DAO approval.

Redeeming USDs

Redeeming 1 USDs at the protocol level gives the user back any one unit of collateral (maximum 1 unit of collateral) after deducting the redemption fee. Redeemers can choose from the list of eligible collaterals that they want to receive. A portion of USDs redeemed is collected as a redemption fee by the protocol.

The protocol will redeem 1 USDs following this simple equation:

Fee = x% of USDs amount redeemed. 'x' depends on the selected collateral.

Collateral tokens redeemed = (1-x)% * (No. of USDs redeemed)

When a collateral token is worth more than 1 dollar, it will be treated with its actual market price. However, when it is worth less than 1 dollar, it will be treated as 1 dollar. Hence, USDs will always be fully collateralized or over-collateralized.

The aggregate collateral ratio (or CR = Total Value Locked/USDs Circulating Supply) should be close to 100% as USDs are backed by stablecoins and collateral is expected to hold their price even in situations of market volatility. However, in an extreme situation if the value of locked collateral changes and the collateral ratio drops by more than 10%, the protocol will be paused manually. Redemptions will begin based on governance or if the collateral ratio increases. To cover any gaps in collateralization SPA reserves from Treasury may be used by the protocol.

Redemption fees are subject to Sperax DAO approval.

Caps

While minting USDs, if the price of the collateral token is more than 1 USD, then USDs will treat the price of the collateral as 1 USD and will only mint 1 USDs per collateral token deposited. But if the price of the collateral is less than 1 USD then more units of the collateral will be required to mint a unit of USDs. In that case minters would need to provide 1 USD worth of collateral to mint 1 USDs. If the price of the collateral has dropped below 0.97 cents then users would not be able to use that collateral to mint USDs. While redeeming users would always receive one unit of any collateral token of their choice for one unit of USDs.

Fees

Fees will be calculated and configurable based on the current state of the protocol’s collateral composition. Anyone would be able to call a function that updates the fee parameters. When a collateral would exceed the desired collateral composition the fee for that collateral would increase and its redemption fee would decrease. Similarly when the amount of collateral in the protocol is less than the desired amount, the mint fee for that collateral will decrease and the redemption fee would increase. Initially all collaterals except for USDC will be set to have a desired collateral composition of 20% and the base fee will be set to 0.05%. Any collateral having a composition of greater than the desired collateral composition cap will have a mint fee of greater than the base fee. The exact applicable fee on a collateral will vary and can be queried via a view function in the contract.

x: Current collateral value in number of tokens

Ca: (Desired collateral composition in % x Total Collateral in the Vault)

Total collateral in vault = Total USDs supply

Base mint and redeem fee (f base): Base fee for mint and redemption which will be discounted/increased dynamically based on the collaterals composition.

Redeeming from Strategies

Now users can redeem their choice of collateral from any yield strategy, instead of relying on a preset default mechanism. Strategies are a set of smart contracts that control the depositing and withdrawal of collaterals from various other DeFi protocols like Aave, Compound, Curve etc.. The slippage that occurs is still transferred back to the redeemers but since redeemers have a choice, they could calculate and manage their own slippage. Withdrawing from single sided strategies like Aave and compound could have significantly less slippage as compared to withdrawing from complex liquidity pool strategies like Curve.

Auto-yield is distributed after a user redeems and before a user mints. So minters and redeemers should check if there’s an eligible auto-yield.

USDs stands out from other stablecoins thanks to its inflation fighting Auto-Yield feature. USDs is novel in the stablecoin ecosystem, because it requires no action by the user. Users do not need to stake USDs nor spend gas to claim their yield. One simply holds USDs, and their wallet balance will grow.

The collateral received for minting USDs is deployed in other audited, defi projects to generate organic yield. USDs collateral earns yield in the form of reward tokens and swapping fees from the pools. This yield is shared between USDs holders and SPA stakers (The split is 50% for Auto-Yield and 50% for SPA buyback and burns. This share can be changed through governance).

Gas free yield: 50% of yield generated on USDs collateral is used to mint USDs. This USDs is distributed to anyone who holds USDs in their wallet.

The actual yield generated depends on the yield rate of the strategies where collateral is deployed. However, the protocol will try to maintain a target yield of 11% APY (maximum) so that USDs holders get stable returns irrespective of market conditions. Any yield generated over 11% is stored in the protocol to help fund the APY for lean periods when actual yield generated is less than 11%.

Yield Strategies

Different yield generation strategies are proposed by the community/team and evaluated by the community based on their yield generation potential, risk profile etc. Community then votes to choose pools/farms where collateral will be deployed. Following strategies are being used for yield generation. We will keep updating this list to include newer strategies approved by the community.

Strategy list as per SIP-55:

• USDC:

  • Compound (USDC)

  • Aave (USDC)

  Maximum cap of 75% of total USDC collateral for each strategy.

• USDC.e:

  • Compound (USDC.e)

  • Stargate (Stargate-LP USDC.e)

  • Aave (USDC.e)

  • Curve (FRAX-USDC.E)

  Maximum cap of 50% of total USDC.e collateral for each strategy.

• DAI:

  • Aave (DAI)

  • Radiant V2 (DAI)

  Maximum cap of 75% of total DAI collateral for each strategy.

• USDT:

  • Aave (USDT)

  • Stargate (Stargate-LP USDT)

  Maximum cap of 75% of total USDT collateral for each strategy.

• FRAX:

  • Frax (Curve-LP FRAX/VST)

  • Curve (FRAX-USDC.E)

  Maximum cap of 75% of total FRAX collateral for each strategy.

• LUSD:

  • Camelot (LUSD-USDC V2 Pool)

  • Aave (LUSD).

  Maximum cap of 75% of total LUSD collateral for each strategy.

Old strategies that are not in use / deprecated:

Curve | Curve-LP USDC/USDT [Not in use]

Saddle | Saddle-LP FRAX/USDC [Saddle sunset] Frax | Curve-LP FRAX/VST [Vesta sunset]

Eligibility

USDs held in EOA wallets, i.e. non-contract addresses, will receive auto-yield on a regular basis. For now, USDs that are deployed by users to yield-earning strategies within the Sperax suite of yield farms will not receive auto-yield.

By default, smart contracts holding USDs are not included in the yield distribution process and do not earn any yield. A smart contract’s USDs balance remains the same after an auto-yield distribution event. However, based on community’s feedback and once approved by veSPA holders via Snapshot voting, the Sperax team can whitelist specific smart contracts to be part of auto-yield, and provide technical support to determine whether a protocol is compatible with the auto-yield feature of USDs.

Auto-yield distribution mechanism

USDs follows the ERC20 token standard. A wallet holding USDs should expect its USDs balance to increase automatically over time. This increase is triggered by a distribution event that happens on average every 7 days. The earned USDs are not explicitly transferred into the user’s wallet, instead a global parameter is changed to update the holder's balance.

Unlike most ERC20, where the token contract directly stores the amount of tokens each wallet holds, USDs’ token contract has a shared state variable creditPerToken, and the contract stores each wallet’s credit. A wallet’s balance = credit / creditPerToken.

When yield is generated:

1. The yield is swapped for USDs in the open market

2. The USDs from step (1) is burned

3. The value of creditPerToken is *decreased globally and therefore every wallet’s balance increases (since every wallet’s credit is unchanged during this process)

*: creditPerToken is decreased according to the amount of USDs burnt in step (2) such that total supply of USDs remains unchanged after steps (2) and (3)

The circulating supply of USDs remains unchanged through this process as the USDs that are bought from the market are burnt and then the USDs balance of the holders increase proportionally. As a result, a user can expect its USDs balance to increase automatically over time without any additional USDs explicitly being transferred to the user’s wallet.

Yield distribution frequency

Yield is distributed approximately every 7 days. The exact distribution time is determined in a quasi-random way. We have decided on this randomised distribution time to prevent users from timing their USDs minting and redeeming with yield distribution events. Huge spike in minting or redeeming around the time of yield distribution can put strain on the peg and this randomisation works as a defence mechanism for maintaining peg.

Externally owned accounts (EOAs) holding USDs were always eligible for the Auto-yield feature, but smart contract / smart wallets were not.

Sperax has introduced a new function: now smart accounts (or smart wallets) can call to opt in for auto rebase in USDs contract and to get Auto-yield.

An owners of a smart contract / smart wallet can opt in for rebase in USDs contract. The users will not need to claim (or send out any transactions to claim) the interest earned.

This is how to opt in your smart contract / smart wallet for rebase in USDs:

1. Go to Arbiscan and search for USDs. Verify the correct USDs contract address: 0xD74f5255D557944cf7Dd0E45FF521520002D5748

2. Go to the Token contract. ensure it is Sperax USD (USDs) deployed by Sperax Deployer 0x42d2f9f84EeB86574aA4E9FCccfD74066d809600

3. Click on the contract and make sure your account is connected (Metamask, Gnosis Safe, or any other smart account).

4. Go to “Write as Proxy”.

5. Connect your wallet (choose WalletConnect, Coinbase Wallet, or any other wallet).

6. Once connected, you will see two functions with the same name: rebaseOptIn You don’t have to call the first function because it’s an owner-only function (can be called only by the USDs owner). Instead, click the second function rebaseOptIn. This allows you to opt in for rebase for your own account (your smart contract account).

7. Confirm the transaction, and your smart account will be opted in for auto rebase.

That’s it. Your smart account / smart wallet is eligible for auto-yield!

1. Cap/Floor collateral value to $1 while minting/redeeming 1 USDs

Minting 1 USDs - If a collateral token is worth less than $1, it will be treated with its actual market price. However, if it is worth more than 1 dollar, it will be treated as $1.

Redeeming 1 USDs - If a collateral token is worth more than $1, it will be treated with its actual market price. However, if it is worth less than 1 dollar, it will be treated as 1 units of collateral at its market price.

Hence, USDs will always be fully collateralized or over-collateralized. For more information on how mint and redeem functions work check outMinting and Redeeming

2. Redemption Fee

The protocol collects a redemption fee whenever USDs is redeemed. This fee is passed on to the SPA stakers. Redemption fee is levied so that protocol does not work like a free token swap instrument. The fee is static for each collateral token but can be upgraded through governance by the community. It is a percentage of the transaction value.

1. Mint Fee = 0

2. Redemption Fee = x% of the amount of USDs redeemed.

x depends on the selected collateral. Check the current redemption fee for the USDs in app.sperax.io

3. Pause minting USDs with de-pegged collateral

If the collateral being used to mint USDs has de-pegged by 2% or more to the downside then protocol will stop minting USDs using that collateral.

4. Auto-yield for USDs holders

As more people use USDs, the yield rate will serve as a second-layer protection from a high selling pressure, further empowering a mass adoption in various use cases including payment, derivatives, and portfolio construction. For more information on how auto-yield works check out Auto Yield

5. Mint SPA when sufficient collateral is not available

When sufficient collateral is not available, USDs redeemers would get $1 worth of collateral in the form of SPA tokens. This would be the collateral of last resort.

Key parameters upgradeable via governance

• Collateral types to mint/ redeem USDs.

• Desired collateral composition, oracle used for price feed of the collateral, base Mint Fee, base Redemption Fee and price floor for each collateral type. Updating the price floor for collateral used to mint USDs. Setting the price floors for each collateral will allow the protocol to remain solvent when collaterals depeg. The protocol will not mint USDs with the collateral when the price of the collateral falls below the price floor.

• Yield generation strategies for each collateral type. For example, adding new delta-neutral yield farming strategies based on other decentralized exchanges.

• Harvesting incentive.

• The USDs dripping rate from the dripper contract.

• Minimum and maximum APR for distribution of Auto-Yield.

Key functions available to the public

• Harvesting or claiming all kinds of yield tokens from the yield generation strategies. The harvester will be incentivized with a portion of the yield-farmed tokens.

• Purchase harvested yield tokens for market price. We will use the respective oracles for the yield tokens to determine the market price. This experience will be similar to the currently implemented buyback contract.

• Distributing the auto-yield to all addresses eligible to collect it. Rebase will also be triggered when someone Mints or Redeems.

This technical document is about the upgrade to USDs-v2. It details the changes made to enhance the protocol's decentralization, transparency, security, and scalability. The document covers new features and functionalities.

USDs

• ERC20 contract

• USDs is a stable coin which generates auto-yield natively.

• USDs is a rebasing token with two modes of accounting for users:

  • Rebasing wallets

    • Users holding tokens in their EOA are by default in this category and are eligible for auto-yield via a rebasing mechanism.

    • Any contract opted-in for rebase also comes in this category.

    • Balance for this category is tracked via a credit system, as described below :

    $$creditsPerToken = C_t \\ creditBalance = C_b \\ userBalance = C_b/C_t$$

    • creditsPerToken is tracked at a global level and is updated when doing a rebase.

    • creditBalance is tracked at an account level and is updated via token transfer, mint, redemption of USDs

  • Non-Rebasing wallets

    • For Non-Rebasing wallets this token acts as a normal ERC20 token and tracks the balance of the wallet as usual.

• Rebasing Mechanism

  • Users mint USDs using approved list of collaterals

  • These collaterals accumulated in the USDs vault are then deployed to various yield on-chain earning opportunities.

  • Yield is harvested periodically and is used to buyback USDs from the market of which 50% is used as revenue for veSPA holders and rest of it goes for USDs auto yield.

  • While doing a rebase the x amount of USDs is partially burnt (without changing the overall total supply) and the creditsPerToken value is adjusted such that the burnt amount is proportionally distributed across all rebasing wallets.

Contract Documentation

Inherits: ERC20PermitUpgradeable, OwnableUpgradeable, ReentrancyGuardUpgradeable, IUSDs

Author: Sperax Foundation

ERC20 compatible contract for USDs supporting the rebase feature. This ERC20 token represents USDs on the Arbitrum (L2) network. Note that the invariant holds that the sum of balanceOf(x) for all x is not greater than totalSupply(). This is a consequence of the rebasing design. Integrations with USDs should be aware of this feature.

Inspired by OUSD: https://github.com/OriginProtocol/origindollar/blob/master/contracts/contracts/token/OUSD.sol

State Variables

MAX_SUPPLY

uint256 private constant MAX_SUPPLY = ~uint128(0);

_totalSupply

uint256 internal _totalSupply;

_deprecated_vars

uint256[4] private _deprecated_vars;

_allowances

mapping(address => mapping(address => uint256)) private _allowances;

vault

address public vault;

_creditBalances

mapping(address => uint256) private _creditBalances;

_deprecated_rebasingCredits

uint256 private _deprecated_rebasingCredits;

rebasingCreditsPerToken

uint256 public rebasingCreditsPerToken;

nonRebasingSupply

uint256 public nonRebasingSupply;

nonRebasingCreditsPerToken

mapping(address => uint256) public nonRebasingCreditsPerToken;

rebaseState

mapping(address => RebaseOptions) public rebaseState;

_deprecated_gatewayAddr

address[2] private _deprecated_gatewayAddr;

_deprecated_isUpgraded

mapping(address => bool) private _deprecated_isUpgraded;

paused

bool public paused;

Functions

onlyVault

Verifies that the caller is the Savings Manager contract.

modifier onlyVault();

constructor

constructor();

initialize

Initializes the contract with the provided name, symbol, and vault address.

function initialize(string memory _nameArg, string memory _symbolArg, address _vaultAddress) external initializer;

Parameters

mint

Mints new USDs tokens, increasing totalSupply.

function mint(address _account, uint256 _amount) external override onlyVault nonReentrant;

Parameters

burn

Burns tokens, decreasing totalSupply.

function burn(uint256 _amount) external override nonReentrant;

Parameters

rebaseOptIn

Voluntary opt-in for rebase.

Useful for smart-contract wallets.

function rebaseOptIn() external;

rebaseOptOut

Voluntary opt-out from rebase.

function rebaseOptOut() external;

rebaseOptIn

Adds _account to the rebasing account list.

function rebaseOptIn(address _account) external onlyOwner;

Parameters

rebaseOptOut

Adds _account to the non-rebasing account list.

function rebaseOptOut(address _account) external onlyOwner;

Parameters

rebase

The rebase function. Modifies the supply without minting new tokens. This uses a change in the exchange rate between "credits" and USDs tokens to change balances.

function rebase(uint256 _rebaseAmt) external override onlyVault nonReentrant;

Parameters

updateVault

Change the vault address.

function updateVault(address _newVault) external onlyOwner;

Parameters

pauseSwitch

Called by the owner to pause or unpause the contract.

function pauseSwitch(bool _pause) external onlyOwner;

Parameters

transfer

Transfer tokens to a specified address.

function transfer(address _to, uint256 _value) public override returns (bool);

Parameters

Returns

transferFrom

Transfer tokens from one address to another.

function transferFrom(address _from, address _to, uint256 _value) public override returns (bool);

Parameters

Returns

approve

Approve the passed address to spend the specified amount of tokens on behalf of msg.sender. This method is included for ERC20 compatibility.

increaseAllowance and decreaseAllowance should be used instead. Changing an allowance with this method brings the risk that someone may transfer both the old and the new allowance - if they are both greater than zero - if a transfer transaction is mined before the later approve() call is mined.

function approve(address _spender, uint256 _value) public override returns (bool);

Parameters

Returns

increaseAllowance

Increase the amount of tokens that an owner has allowed a _spender to spend. This method should be used instead of approve() to avoid the double approval vulnerability described above.

function increaseAllowance(address _spender, uint256 _addedValue) public override returns (bool);

Parameters

Returns

decreaseAllowance

Decrease the amount of tokens that an owner has allowed a _spender to spend.

function decreaseAllowance(address _spender, uint256 _subtractedValue) public override returns (bool);

Parameters

Returns

totalSupply

Check the current total supply of USDs.

function totalSupply() public view override(ERC20Upgradeable, IUSDs) returns (uint256);

Returns

balanceOf

Gets the USDs balance of the specified address.

function balanceOf(address _account) public view override returns (uint256);

Parameters

Returns

creditsBalanceOf

Gets the credits balance of the specified address.

function creditsBalanceOf(address _account) public view returns (uint256, uint256);

Parameters

Returns

allowance

Function to check the amount of tokens that an owner has allowed a spender.

function allowance(address _owner, address _spender) public view override returns (uint256);

Parameters

Returns

_mint

Creates _amount tokens and assigns them to _account, increasing the total supply.

Emits a {Transfer} event with from set to the zero address.

Requirements - to cannot be the zero address.

function _mint(address _account, uint256 _amount) internal override;

Parameters

_burn

Destroys _amount tokens from _account, reducing the total supply.

Emits a {Transfer} event with to set to the zero address.

• Requirements:

• _account cannot be the zero address.

• _account must have at least _amount tokens.*

function _burn(address _account, uint256 _amount) internal override;

Parameters

_executeTransfer

For non-rebasing accounts credit amount = _amount

Update the count of non-rebasing credits in response to a transfer

function _executeTransfer(address _from, address _to, uint256 _value) private;

Parameters

_rebaseOptIn

Add a contract address to the non-rebasing exception list. I.e., the address's balance will be part of rebases so the account will be exposed to upside and downside.

function _rebaseOptIn(address _account) private;

Parameters

_rebaseOptOut

Remove a contract address from the non-rebasing exception list.

function _rebaseOptOut(address _account) private;

_isNonRebasingAccount

Is an account using rebasing accounting or non-rebasing accounting? Also, ensure contracts are non-rebasing if they have not opted in.

function _isNonRebasingAccount(address _account) private returns (bool);

Parameters

_ensureNonRebasingMigration

Ensures internal account for rebasing and non-rebasing credits and supply is updated following the deployment of frozen yield change.

function _ensureNonRebasingMigration(address _account) private;

Parameters

_balanceOf

Calculates the balance of the account.

Function assumes the _account is already upgraded.

function _balanceOf(address _account) private view returns (uint256);

Parameters

_creditsPerToken

Get the credits per token for an account. Returns a fixed amount if the account is non-rebasing.

function _creditsPerToken(address _account) private view returns (uint256);

Parameters

_isNotPaused

Validates if the contract is not paused.

function _isNotPaused() private view;

Events

TotalSupplyUpdated

event TotalSupplyUpdated(uint256 totalSupply, uint256 rebasingCredits, uint256 rebasingCreditsPerToken);

Paused

event Paused(bool isPaused);

VaultUpdated

event VaultUpdated(address newVault);

RebaseOptIn

event RebaseOptIn(address indexed account);

RebaseOptOut

event RebaseOptOut(address indexed account);

Errors

CallerNotVault

error CallerNotVault(address caller);

ContractPaused

error ContractPaused();

IsAlreadyRebasingAccount

error IsAlreadyRebasingAccount(address account);

IsAlreadyNonRebasingAccount

error IsAlreadyNonRebasingAccount(address account);

CannotIncreaseZeroSupply

error CannotIncreaseZeroSupply();

InvalidRebase

error InvalidRebase();

TransferToZeroAddr

error TransferToZeroAddr();

TransferGreaterThanBal

error TransferGreaterThanBal(uint256 val, uint256 bal);

MintToZeroAddr

error MintToZeroAddr();

MaxSupplyReached

error MaxSupplyReached(uint256 totalSupply);

Enums

RebaseOptions

enum RebaseOptions {
    NotSet,
    OptOut,
    OptIn
}

Inherits: Initializable, OwnableUpgradeable, ReentrancyGuardUpgradeable

Author: Sperax Foundation

This contract allows users to exchange SPA tokens for USDs tokens.

Users can provide SPA tokens and receive USDs tokens in return based on the current exchange rate.

A percentage of the provided SPA tokens are distributed as rewards, and the rest are burned.

State Variables

veSpaRewarder

rewardPercentage

oracle

Functions

constructor

initialize

Contract initializer

Parameters

withdraw

Emergency withdrawal function for unexpected situations

Can only be called by the owner

Parameters

updateRewardPercentage

Changes the reward percentage

Example value for _newRewardPercentage = 5000 for 50%

Parameters

updateVeSpaRewarder

Update veSpaRewarder address

Parameters

updateOracle

Update oracle address

Parameters

buyUSDs

Function to buy USDs for SPA for frontend

Parameters

getSPAReqdForUSDs

Calculates and returns SPA amount required for _usdsAmount

Parameters

Returns

buyUSDs

Buy USDs for SPA if you want a different receiver

Parameters

distributeAndBurnSPA

Sends available SPA in this contract to rewarder based on rewardPercentage and burns the rest

getUsdsOutForSpa

Returns the amount of USDS for SPA amount in

Parameters

Returns

_getUsdsOutForSpa

Returns the amount of USDS for SPA amount in

Parameters

Returns

_getOracleData

Retrieves price data from the oracle contract for SPA and USDS tokens.

Returns

_isValidRewardPercentage

Checks if the provided reward percentage is valid.

The reward percentage must be a non-zero value and should not exceed the maximum percentage value.

Parameters

Events

BoughtBack

Withdrawn

SPARewarded

SPABurned

RewardPercentageUpdated

VeSpaRewarderUpdated

OracleUpdated

Errors

CannotWithdrawSPA

InsufficientUSDsBalance

Inherits: Ownable, IOracle

Author: Sperax Foundation

Communicates with different price feeds to get the price

State Variables

tokenPriceFeed

Store price feed data for tokens.

Functions

updateTokenPriceFeed

Add/Update price feed for _token

Have to be extra cautious while updating the price feed.

Parameters

removeTokenPriceFeed

Remove an existing price feed for _token.

Parameters

getPrice

Gets the price feed for _token.

Function reverts if the price feed does not exists.

Parameters

Returns

priceFeedExists

Validates if price feed exists for a _token

Function reverts if price feed not set.

Parameters

Returns

_getPriceFeed

Gets the price feed for a _token given the feed data.

Parameters

Returns

Events

PriceFeedUpdated

PriceFeedRemoved

Errors

InvalidAddress

UnableToFetchPriceFeed

InvalidPriceFeed

PriceFeedNotFound

Inherits: IFeeCalculator

Author: Sperax Foundation

A contract that calculates fees for minting and redeeming USDs.

State Variables

LOWER_THRESHOLD

UPPER_THRESHOLD

DISCOUNT_FACTOR

PENALTY_MULTIPLIER

CALIBRATION_GAP

COLLATERAL_MANAGER

collateralFee

Functions

constructor

calibrateFee

Calibrates fee for a particular collateral

Parameters

getMintFee

Calculates fee to be collected for minting

Parameters

Returns

getRedeemFee

Calculates fee to be collected for redeeming

Parameters

Returns

calibrateFeeForAll

Calibrates fee for all the collaterals registered

_calibrateFee

Helper function for calibrating fee for a collateral

Parameters

Events

FeeCalibrated

Errors

InvalidCalibration

Structs

FeeData