# Classic Farms

`MasterChefERC20` is a per-block MasterChef for **fungible LP tokens** — today
that means [stable-pool LP](/stable-pools), and any future classic AMM LP.

| | |
| --- | --- |
| Contract | `MasterChefERC20` — `0x70b9144e1378d872063d2BBfCA61f378A9b2d163` |
| Stake | ERC-20 LP tokens (`StableSwapLP`) |
| Rewards | BSCT, minted per block |

## Reward model

Every block, the farm mints `bscttPerBlock` BSCT and splits it across pools by
allocation points:

```
poolRewardPerBlock = bscttPerBlock × pool.allocPoint / totalAllocPoint
accBscttPerShare  += poolRewardPerBlock × 1e12 / lpSupply
pending            = user.amount × accBscttPerShare / 1e12 − user.rewardDebt
```

Your share of a pool's emissions equals your share of its staked LP supply.

## Using a farm

:::steps
### Approve

Approve the LP token to the MasterChef once:

```ts
await lpToken.write.approve([MASTERCHEF_ERC20, maxUint256])
```

### Deposit

```solidity
function deposit(uint256 pid, uint256 amount) external nonReentrant;
```

Depositing also harvests any pending BSCT automatically.

### Harvest

Deposit **zero** to claim rewards without changing your stake:

```ts
await masterChef.write.deposit([pid, 0n]) // harvest-only pattern
```

### Withdraw

```solidity
function withdraw(uint256 pid, uint256 amount) external nonReentrant;
```

Withdrawal also harvests pending rewards.
:::

:::warning[Emergency exit]
`emergencyWithdraw(pid)` returns your LP immediately but **forfeits all
pending BSCT**. Only for emergencies.
:::

## Contract interface

### Structs

```solidity
struct PoolInfo {
    IERC20  lpToken;          // staked LP token
    uint256 allocPoint;       // weight vs other pools
    uint256 lastRewardBlock;
    uint256 accBscttPerShare; // scaled by 1e12
}

struct UserInfo {
    uint256 amount;      // LP staked
    uint256 rewardDebt;  // harvest checkpoint
}
```

### User & view functions

```solidity
function deposit(uint256 pid, uint256 amount) external nonReentrant;
function withdraw(uint256 pid, uint256 amount) external nonReentrant;
function emergencyWithdraw(uint256 pid) external nonReentrant;

function pendingBsctt(uint256 pid, address user) external view returns (uint256);
function poolLength() external view returns (uint256);
function poolInfo(uint256 pid) external view returns (PoolInfo memory);
function userInfo(uint256 pid, address user) external view returns (UserInfo memory);
```

### Admin functions

```solidity
/// Add a new LP pool. Always pass withUpdate=true in production.
function add(uint256 allocPoint, IERC20 lpToken, bool withUpdate) external onlyOwner;

/// Re-weight a pool
function set(uint256 pid, uint256 allocPoint, bool withUpdate) external onlyOwner;

/// Change the global emission rate
function updateEmissionRate(uint256 bscttPerBlock) external onlyOwner;
```

## APR calculation

```
farmAPR = bscttPerBlock × blocksPerYear × (allocPoint / totalAllocPoint) × bscttPrice
        ──────────────────────────────────────────────────────────────────────────────
        stakedLpSupply × lpTokenPrice
```

For stable LP, `lpTokenPrice ≈ virtualPrice × pegPrice` — see
[Providing Liquidity](/stable-pools/providing-liquidity#how-value-accrues-virtual-price).

## Live classic farms — ARC Testnet

| pid | LP | Alloc points |
| --- | --- | --- |
| 0 | USDC/EURC stable LP — `0x225057406e3C7D3f3196EC13fC82ed04E2D647Dd` | 100 |