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Chronicle Protocol provides verifiable, cost-efficient oracle price feeds. Chronicle contracts are read-protected by a whitelist.

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Prerequisites

  • A Solidity contract targeting Polygon zkEVM Cardona testnet or mainnet.
  • On testnet: your contract address must be added to the whitelist using the SelfKisser contract (see step 1 below).
  • On mainnet: open a support ticket on Discord in the #support channel to request whitelist access.
Find deployment addresses on the Chronicle Dashboard.

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Read POL/USD price from Chronicle

The contract below reads the POL/USD price on the zkEVM Cardona testnet and handles whitelist registration automatically in the constructor. 
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.16;

/**
 * @title OracleReader
 * @notice A simple contract to read from Chronicle oracles
 * @dev To see the full repository, visit https://github.com/chronicleprotocol/OracleReader-Example.
 * @dev Addresses in this contract are hardcoded for the zkEVM Cardona Testnet.
 * For other supported networks, check the https://chroniclelabs.org/dashboard/oracles.
 */
contract OracleReader {
    /**
    * @notice The Chronicle oracle to read from.
    * Chronicle_POL_USD_1 - 0x55a07a60cd9ed198B5Ba4360FF9800eBb6667388
    * Network: zkEVM Cardona Testnet
    */

    IChronicle public chronicle = IChronicle(address(0x55a07a60cd9ed198B5Ba4360FF9800eBb6667388));

    /**
    * @notice The SelfKisser granting access to Chronicle oracles.
    * SelfKisser_1:0xCce64A8127c051E784ba7D84af86B2e6F53d1a09
    * Network: zkEVM Cardona Testnet
    */
    ISelfKisser public selfKisser = ISelfKisser(address(0xCce64A8127c051E784ba7D84af86B2e6F53d1a09));

    constructor() {
        // Note to add address(this) to chronicle oracle's whitelist.
        // This allows the contract to read from the chronicle oracle.
        selfKisser.selfKiss(address(chronicle));
    }

    /**
    * @notice Function to read the latest data from the Chronicle oracle.
    * @return val The current value returned by the oracle.
    * @return age The timestamp of the last update from the oracle.
    */
    function read() external view returns (uint256 val, uint256 age) {
        (val, age) = chronicle.readWithAge();
    }
}

// Copied from [chronicle-std](https://github.com/chronicleprotocol/chronicle-std/blob/main/src/IChronicle.sol).
interface IChronicle {
    /**
    * @notice Returns the oracle's current value.
    * @dev Reverts if no value set.
    * @return value The oracle's current value.
    */
    function read() external view returns (uint256 value);

    /**
    * @notice Returns the oracle's current value and its age.
    * @dev Reverts if no value set.
    * @return value The oracle's current value using 18 decimals places.
    * @return age The value's age as a Unix Timestamp .
    * */
    function readWithAge() external view returns (uint256 value, uint256 age);
}

// Copied from [self-kisser](https://github.com/chronicleprotocol/self-kisser/blob/main/src/ISelfKisser.sol).
interface ISelfKisser {
    /// @notice Kisses caller on oracle `oracle`.
    function selfKiss(address oracle) external;
}

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Next steps

For more integration examples, see the Chronicle documentation portal.