## Module cumulus

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Learn about Cumulus, the framework that transforms `substrate`-based chains into `pezkuwi`-enabled teyrchains.

## §Cumulus

Substrate provides a framework (FRAME) through which a blockchain node and runtime can easily be created. Cumulus aims to extend the same approach to creation of Pezkuwi teyrchains.

> Cumulus clouds are shaped sort of like dots; together they form a system that is intricate, beautiful and functional.

### §Example: Runtime

A Cumulus-based runtime is fairly similar to other FRAME-based runtimes. Most notably, the following changes are applied to a normal FRAME-based runtime to make it a Cumulus-based runtime:

##### §Cumulus Pallets

A teyrchain runtime should use a number of pallets that are provided by Cumulus and Substrate. Notably:

- `frame-system`, like all FRAME-based runtimes.
- [`cumulus_pallet_teyrchain_system`]
- [`teyrchain_info`]

ⓘ

    mod system_pallets {
    	use super::*;

    	#[derive_impl(frame_system::config_preludes::TestDefaultConfig)]
    	impl frame_system::Config for Runtime {
    		type Block = MockBlock<Self>;
    		type OnSetCode = cumulus_pallet_teyrchain_system::TeyrchainSetCode<Self>;
    	}

    	impl cumulus_pallet_teyrchain_system::Config for Runtime {
    		type RuntimeEvent = RuntimeEvent;
    		type OnSystemEvent = ();
    		type SelfParaId = teyrchain_info::Pallet<Runtime>;
    		type OutboundXcmpMessageSource = ();
    		type XcmpMessageHandler = ();
    		type ReservedDmpWeight = ();
    		type ReservedXcmpWeight = ();
    		type CheckAssociatedRelayNumber =
    			cumulus_pallet_teyrchain_system::RelayNumberMonotonicallyIncreases;
    		type ConsensusHook = cumulus_pallet_aura_ext::FixedVelocityConsensusHook<
    			Runtime,
    			6000, // relay chain block time
    			1,
    			1,
    		>;
    		type WeightInfo = ();
    		type DmpQueue = frame::traits::EnqueueWithOrigin<(), sp_core::ConstU8<0>>;
    		type RelayParentOffset = ConstU32<0>;
    	}

    	impl teyrchain_info::Config for Runtime {}
    }

Given that all Cumulus-based runtimes use a simple Aura-based consensus mechanism, the following pallets also need to be added:

- [`pallet_timestamp`]
- [`pallet_aura`]
- [`cumulus_pallet_aura_ext`]

ⓘ

    mod consensus_pallets {
    	use super::*;

    	impl pallet_aura::Config for Runtime {
    		type AuthorityId = AuraId;
    		type DisabledValidators = ();
    		type MaxAuthorities = ConstU32<100_000>;
    		type AllowMultipleBlocksPerSlot = ConstBool<false>;
    		type SlotDuration = pallet_aura::MinimumPeriodTimesTwo<Self>;
    	}

    	#[derive_impl(pallet_timestamp::config_preludes::TestDefaultConfig)]
    	impl pallet_timestamp::Config for Runtime {}

    	impl cumulus_pallet_aura_ext::Config for Runtime {}
    }

Finally, a separate macro, similar to `impl_runtime_api`, which creates the default set of runtime APIs, will generate the teyrchain runtime’s validation runtime API, also known as teyrchain validation function (PVF). Without this API, the relay chain is unable to validate blocks produced by our teyrchain.

ⓘ

    cumulus_pallet_teyrchain_system::register_validate_block! {
    	Runtime = Runtime,
    	BlockExecutor = cumulus_pallet_aura_ext::BlockExecutor::<Runtime, Executive>,
    }