Spark PSM

Overview

The Spark PSM extends the Sky PSM liquidity on Ethereum mainnet to other chains, starting with Base. It allows swaps between USDS, sUSDS, and USDC with no slippage or fees beyond gas, making it the top liquidity source for these pairs in DeFi. This enables holders of USDC on supported networks to easily acquire sUSDS to earn yield, at no cost beyond gas.

Contract Details

Contract Name: PSM3.sol
Contract Source: Spark PSM code repository

Deployments

Network	Spark PSM Address
Base	0x1601843c5E9bC251A3272907010AFa41Fa18347E

State Variables and Immutables

usdc: IERC20 interface of USDC.
usds: IERC20 interface of USDS.
susds: IERC20 interface of sUSDS. Note that this is an ERC20 and not a ERC4626 because it's not on mainnet.
pocket: Address that holds custody of USDC. The pocket can deploy USDC to yield-bearing strategies. Defaulted to the address of the PSM itself.
rateProvider: Contract that returns a conversion rate between and sUSDS and USD in 1e27 precision. See Cross-chain Savings Rate Oracle for more information.
totalShares: Total shares in the PSM. Shares represent the ownership of the underlying assets in the PSM.
shares: Mapping of user addresses to their shares.

Functions

Admin Functions

setPocket: Sets the pocket address. Only the owner can call this function. This is a very important and sensitive action because it transfers the entire balance of USDC to the new pocket address. OZ Ownable is used for this function, and owner will always be set to the governance proxy.

Swap Functions

swapExactIn: Allows swapping of assets based on current conversion rates, specifying an amountIn of the asset to swap. Ensures the derived output amount is above the minAmountOut specified by the user before executing the transfer and emitting the swap event. Includes a referral code.
swapExactOut: Allows swapping of assets based on current conversion rates, specifying an amountOut of the asset to receive from the swap. Ensures the derived input amount is below the maxAmountIn specified by the user before executing the transfer and emitting the swap event. Includes a referral code.

Liquidity Provision Functions

deposit: Deposits assets into the PSM, minting new shares. Includes a referral code.
withdraw: Withdraws assets from the PSM by burning shares. Ensures the user has sufficient shares for the withdrawal and adjusts the total shares accordingly. Includes a referral code.

Preview Functions

previewDeposit: Estimates the number of shares minted for a given deposit amount.
previewWithdraw: Estimates the number of shares burned and the amount of assets withdrawn for a specified amount.
previewSwapExactIn: Estimates the amount of assetOut received for a given amount of assetIn in a swap.
previewSwapExactOut: Estimates the amount of assetIn required to receive a given amount of assetOut in a swap.

Conversion Functions

convertToAssets: Converts shares to the equivalent amount of a specified asset.
convertToAssetValue: Converts shares to their equivalent value in USD terms with 18 decimal precision.
convertToShares: Converts asset values to shares based on the current exchange rate.

Asset Value Functions

totalAssets: Returns the total value of all assets held by the PSM denominated in USD with 18 decimal precision.

Events

Swap: Emitted on asset swaps.
Deposit: Emitted on asset deposits.
Withdraw: Emitted on asset withdrawals.

Key Mechanisms & Concepts

Fetch Liquidity

You can fetch the liquidity of the PSM3 by checking the USDS and sUSDS ERC20 token balances deposited in the PSM3 contract. USDC liquidity is being kept in the pocket address, but currently this address is set to the PSM3 contract itself, however it could be different in the future.

Pricing

USDS and USDC are always converted at a fixed 1:1 ratio.

sUSDS is a yield accumulating token, meaning its price will increase vs USDS/USDC over time. A rate provider oracle is used to provide the sUSDS price.