> ## Documentation Index
> Fetch the complete documentation index at: https://docs.base.org/llms.txt
> Use this file to discover all available pages before exploring further.

# System Config

> SystemConfig changes in the Holocene upgrade, adding dynamic EIP-1559 parameter configuration via ConfigUpdate events.

## Overview

The `SystemConfig` is updated to allow for dynamic EIP-1559 parameters.

### `ConfigUpdate`

When the configuration is updated, a [`ConfigUpdate`](../../protocol/consensus/derivation#system-config-updates) event
MUST be emitted with the following parameters:

| `version`    | `updateType` | `data`                                                     | Usage                                            |
| ------------ | ------------ | ---------------------------------------------------------- | ------------------------------------------------ |
| `uint256(0)` | `uint8(4)`   | `abi.encode((uint256(_denominator) << 32) \| _elasticity)` | Modifies the EIP-1559 denominator and elasticity |

Note that the above encoding is the format emitted by the SystemConfig event, which differs from the format in extraData
from the block header.

### Initialization

The following actions should happen during the initialization of the `SystemConfig`:

* `emit ConfigUpdate.BATCHER`
* `emit ConfigUpdate.FEE_SCALARS`
* `emit ConfigUpdate.GAS_LIMIT`
* `emit ConfigUpdate.UNSAFE_BLOCK_SIGNER`

Intentionally absent from this is `emit ConfigUpdate.EIP_1559_PARAMS`.
As long as these values are unset, the default values will be used.
Requiring 1559 parameters to be set during initialization would add a strict requirement
that the L2 hardforks before the L1 contracts are upgraded, and this is complicated to manage in a
world of many chains.

### Modifying EIP-1559 Parameters

A new `SystemConfig` `UpdateType` is introduced that enables the modification of
[EIP-1559](https://eips.ethereum.org/EIPS/eip-1559) parameters. This allows for the chain
operator to modify the `BASE_FEE_MAX_CHANGE_DENOMINATOR` and the `ELASTICITY_MULTIPLIER`.

### Interface

#### EIP-1559 Params

##### `setEIP1559Params`

This function MUST only be callable by the chain governor.

```solidity theme={null}
function setEIP1559Params(uint32 _denominator, uint32 _elasticity)
```

The `_denominator` and `_elasticity` MUST be set to values greater to than 0.
It is possible for the chain operator to set EIP-1559 parameters that result in poor user experience.

##### `eip1559Elasticity`

This function returns the currently configured EIP-1559 elasticity.

```solidity theme={null}
function eip1559Elasticity()(uint32)
```

##### `eip1559Denominator`

This function returns the currently configured EIP-1559 denominator.

```solidity theme={null}
function eip1559Denominator()(uint32)
```