Price Feed Sources

Just as adapters interact with external "integratees," so do price feeds interact with sources that provide them with the data they need to provide rates.

AavePriceFeed

Prices Aave aTokens , which are pegged 1:1 with the value of their underlying, e.g., 1 aAAVE is equal to 1 AAVE . aTokens accrue interest via a formulaic rebasing mechanism.

Docs: https://docs.aave.com/developers/the-core-protocol/atokens​

Mainnet contracts:

ProtocolDataProvider : 0x057835Ad21a177dbdd3090bB1CAE03EaCF78Fc6d

Considerations: Always directly returns the input amount as the output amount (i.e., 1:1 pegging)

AlphaHomoraV1PriceFeed

Provides a price for ibETH .

Docs: https://github.com/AlphaFinanceLab/alphahomora/blob/master/contracts/5/Bank.sol​

Mainnet contracts:

Bank (ibETH): 0x67B66C99D3Eb37Fa76Aa3Ed1ff33E8e39F0b9c7A

Considerations: Uses cached rate

ChainlinkPriceFeed

Each rate pair (we use those quoted in either USD or ETH) is provided by a Chainlink "aggregator," and we interact with the proxy contracts for those aggregators.

Docs: https://docs.chain.link/docs/using-chainlink-reference-contracts​

Mainnet contracts: each aggregator

Considerations:

We do not check timestamps on every price lookup, rather we provide a function to allow quickly removing an aggregator that is considered to be stale. If an aggregator is removed, the corresponding primitive will cease to produce a price from the feed and will revert, causing any function that relies on that price to fail until it is re-instituted. This is the desired behavior.

ChaiPriceFeed

This price feed mimics how Chai determines its rate in its codebase, by interacting with Maker DAO's DSR Pot contract.

Docs: https://github.com/dapphub/chai​

Mainnet contracts:

Pot - 0x197E90f9FAD81970bA7976f33CbD77088E5D7cf7

Considerations:

We do not call Pot.drip() before calculating price as in Chai, in order to save gas (drip() updates storage). The CHAI-DAI rate changes negligibly for even long periods of time.

CompoundPriceFeed

Queries each Compound Token (cToken) directly for its rate.

Docs: https://compound.finance/docs​

Mainnet contracts: each cToken

Considerations:

We query the cached rate instead of the live rate for gas savings. Like CHAI, cTokens rates change negligibly for long periods of time.

SynthetixPriceFeed

Queries the Synthetix Exchanger contract to get the rate for a Synth in terms of sUSD .

Docs: https://docs.synthetix.io/​

Mainnet contracts:

• AddressResolver - 0x61166014E3f04E40C953fe4EAb9D9E40863C83AE

Considerations: Live prices

UniswapV2PoolPriceFeed

Uses a special pool manipulation-resistant formula that takes into consideration the current underlying asset balances and pool token balance in the given Uniswap pool (UniswapV2Pair) along with a trusted rate between the two underlying tokens.

Docs: https://uniswap.org/docs/v2/​

Mainnet contracts:

• UniswapV2Factory: 0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f

• instances of UniswapV2Pair

See also the sample implementation we based this on: https://github.com/Uniswap/uniswap-v2-periphery/blob/267ba44471f3357071a2fe2573fe4da42d5ad969/contracts/libraries/UniswapV2LiquidityMathLibrary.sol​

Considerations: Live prices

WDGLDPriceFeed

This price feed uses a known formula for pricing DGLD based on the current rate of XAU. It uses Chainlink aggregators directly.

Docs: https://dgld.ch/​

Mainnet Contracts:

• XAU/USD Aggregator: 0x214eD9Da11D2fbe465a6fc601a91E62EbEc1a0D6

• ETH/USD Aggregator 0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419

Considerations: Live prices