我想用 Chainlink price feed 和 Keepers 去实现一个卖单的自动化，就是当价格低于某一个数值的时候，就触发卖单。这两个函数分开运行分别都可以实现，但是当我把它们放在一起，就无法正常运行了。也就是说当把 Price Feed 放在 CheckUpkeep() 中，performUpKeep()就没法被触发。 checkUpKeep() 函数可以去调用 priceFeed 吗？我应该怎么写这个函数？

代码如下：

function checkUpkeep(bytes memory /* checkData */) public view override returns (//,bytes memory value
        bool upkeepNeeded, 
        bytes memory num
        ){

        uint256 EthPrice = 0;
        // uint256 i = 2;
        EthPrice = getPrice();
        num = abi.encodePacked(EthPrice);
        if (EthPrice > 0){
            upkeepNeeded = true;
        }

        return (upkeepNeeded, num);//, value
    }

    function performUpkeep(bytes calldata num) external override {//, bytes calldata value
        (bool upkeepNeeded, ) = checkUpkeep("");

        if (!upkeepNeeded) {
            revert Order__UpkeepNotNeeded(
                address(this).balance,
                s_Wallets.length
            );
        }
        //Byte conversion to uint
        uint256 number;
        number = abi.decode(num, (uint256));

        // for(uint i=0;i<num.length;i++){
        //     number = number + uint(uint8(num[i]))*(2**(8*(num.length-(i+1))));
        // }
        s_nombre = number;
    }