Introduction

The Open Price Feed accounts price data for the Compound protocol. The protocol's Comptroller contract uses it as a source of truth for prices. Prices are updated by Chainlink Price Feeds. The codebase is hosted on GitHub, and maintained by the community.

The Compound Protocol uses a View contract ("Price Feed") which verifies that reported prices fall within an acceptable bound of the time-weighted average price of the token/ETH pair on Uniswap v2, a sanity check referred to as the Anchor price.

The Chainlink price feeds submit prices for each cToken through an individual ValidatorProxy contract. Each ValidatorProxy is the only valid reporter for the underlying asset price. The contracts can be found on-chain as follows:

Architecture

The Open Price Feed consists of two main contracts.

This architecture allows multiple views to use the same underlying price data, but to verify the prices in their own way.

Stablecoins like USDC, USDT, and TUSD are fixed at $1. SAI is fixed at 0.005285 ETH.

As a precaution, the Compound community multisig has the ability to engage a failover that will switch a market's primary oracle from the Chainlink Price Feeds to Uniswap v2. The multisig is able to change to a failover for single markets. The Uniswap V2 TWAP price is used as the failover. The community can enable or disable the failover using activateFailover or deactivateFailover.

Price

Get the most recent price for a token in USD with 6 decimals of precision.

UniswapAnchoredView

function price(string memory symbol) external view returns (uint)

Solidity

UniswapAnchoredView view = UniswapAnchoredView(0xABCD...);
uint price = view.price("ETH");

Web3 1.0

const view = UniswapAnchoredView.at("0xABCD...");
//eg: returns 200e6
const price = await view.methods.price("ETH").call();

Underlying Price

Get the most recent price for a token in USD with 18 decimals of precision.

UniswapAnchoredView

function getUnderlyingPrice(address cToken) external view returns (uint)

Solidity

UniswapAnchoredView view = UniswapAnchoredView(0xABCD...);
uint price = view.getUnderlyingPrice(0x1230...);

Web3 1.0

const view = UniswapAnchoredView.at("0xABCD...");
//eg: returns 400e6
const price = await view.methods.getUnderlyingPrice("0x1230...").call();

Config

Each token the Open Price Feed supports needs corresponding configuration metadata. The configuration for each token is set in the constructor and is immutable.

The fields of the config are:

UniswapAnchoredView

 function getTokenConfigBySymbol(string memory symbol) public view returns (TokenConfig memory)
 function getTokenConfigBySymbolHash(bytes32 symbolHash) public view returns (TokenConfig memory)
 function getTokenConfigByCToken(address cToken) public view returns (TokenConfig memory)

Web3 1.0

const view = UniswapAnchoredView.at("0xABCD...");
const config = await view.methods.getTokenConfigBySymbol("ETH").call();

Solidity

UniswapAnchoredView view = UniswapAnchoredView(0xABCD...);
uint price = view.getTokenConfigBySymbol("ETH");

Anchor Period

Get the anchor period, the minimum amount of time in seconds over which to take the time-weighted average price from Uniswap.

UniswapAnchoredView

function anchorPeriod() returns (uint)

Web3 1.0

const view = UniswapAnchoredView.at("0xABCD...");
const anchorPeriod = await view.methods.anchorPeriod().call();

Solidity

UniswapAnchoredView view = UniswapAnchoredView(0xABCD...);
uint anchorPeriod = view.anchorPeriod();

Anchor Bounds

Get the highest and lowest ratio of the reported price to the anchor price that will still trigger the price to be updated. Given in 18 decimals of precision (eg: 90% => 90e16).

UniswapAnchoredView

function upperBoundAnchorRatio() returns (uint)
function lowerBoundAnchorRatio() returns (uint)

Web3 1.0

const view = UniswapAnchoredView.at("0xABCD...");
const upperBoundRatio = await view.methods.upperBoundAnchorRatio().call();

Solidity

UniswapAnchoredView view = UniswapAnchoredView(0xABCD...);
uint upperBoundRatio = view.upperBoundAnchorRatio();