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Assets Mapping

Mapping is an important step in the cross-chain transfer of assets. Mapping is the use of smart contracts on two networks (e.g. TRON and BTTC) to match assets one to the other, facilitating operations such as locking, destroying and transferring.

Introduction​

Assets can be moved between BTTC and public chain such as TRON/ Ethereum/ BSC by using BTTC cross-chain bridge. These assets include standard tokens such as ERC20, ERC721 and other customized tokens.

There are generally two situations for assets mapping. The first is that assets already exist on public chains, and assets need to be mapped to BTTC. Please refer to Assets Mapping from Public Chains to BTTC

The other situation is that assets are minted directly on BTTC and need to be moved to other public chain. Please refer to BTTC Mintable Assets Mapping to Public Chain

Assets Mapping from Public Chains to BTTC​

Applicable to the situation that users have deployed assets contracts on public chains TRON/Ethereum/BSC and need to move them to BTTC.

When the assets on public chain has to be moved to BTTC, once a deposit is initiated from the public chain, the ChildChainManagerProxy contract will call the deposit method in the child contract to internally mint the tokens on the child chain. When the assets on BTTC need to be withdrawn, withdraw method in the child contract will be called to internally burn the tokens on the child chain. These rules ensure the assets between two chains maintain balance.

Requirements to be satisfied​

There are a few steps that have to be strictly followed when users need to move assets from contract deployed on public chain to BTTC.

1. Confirm the deployment of root token contract on public chains​

Verify the root token contract deployed on public chain by using Tronscan/Ethscan/Bscscan blockchain explorer.

2. Deploy child token contract on BTTC​

For an example of child token contract to be deployed on BTTC, please refer to ChildERC20. The child token contract can be customized, but please make sure that deposit and withdraw method should be present in custom child contract, meanwhile deposit can only be called by ChildChainManagerProxy contract, with the address on BTTC mainnet, and the address on Donau testnet.

Notice：

  • No token minting in constructor of child token contract. In most cases, tokens do not need to be additional issued on BTTC, only ChildChainManager contract has authority to internally mint the tokens on BTTC（ _setupRole(DEPOSITOR_ROLE, childChainManager) ）.

  • For the cases that tokens do not need to be additional issued on BTTC, if deployed child token contract has extra minting authority, please call revoke or renounce method to abstain. If the extra autority can not be cancelled, please redeploy the contract. The team from BTTC community will review child token contract, and any extra minting authority will lead to failure, because redundant authorization will bring the risk of additional token issuance.

3. Submit Mapping Request​

In the end, please verify the child token contract on Bttcscan, and submit mapping request here.

BTTC Mintable Assets Mapping to Public Chain​

What are BTTC mintable assets?​

New assets can be created on BTTC, and moved to public chain when required, such type of assets are called BTTC mintable assets. Compared to token minting on public chain, creation of assets on BTTC saves much fee and is faster which is a more recommended approach.

When BTTC mintable assets need to be moved to public chain, the assets has to be burned first and a proof of burn transaction has to be submitted on public chain next. The RootChainManager contract then calls a special predicate contract MintableAssetPredicate internally that directly calls the mint function on public chain and the tokens are minted to the users address.

Requirements to be satisfied​

There are a few steps that have to be strictly followed when users need to create assets on BTTC, and move BTTC mintable assets to public chain.

1. Deploy contract on BTTC​

First the mintable assets contract should be deployed on BTTC. For examples of child mintable token contract, please refer to ChildMintableERC20 and ChildMintableERC721. The contract can be customized, but please make sure that deposit, withdraw and mint method are present in the contract.

Most importantly, the ChildChainManager contract on BTTC should be given the DEPOSITOR_ROLE in the mintable asset contract deployed on BTTC, and the authority to deposit tokens can only be called by ChildChainManagerProxy contract, with the address on BTTC mainnet, and the address on Donau testnet.

2. Deploy contract on TRON/Ethereum/BSC​

Then, the corresponding contract should be deployed on TRON/Ethereum/BSC for withdrawl. For examples of contract, please refer to MintableERC20 and MintableERC721.

Most importantly, the MintableAssetPredicateProxy (e.g.： MintableERC20PredicateProxy . Asset represent the asset type, the same as below) contract deployed on TRON/Ethereum/BSC should be given the minter role and have the authorization to mint tokens on public chain.

This role can be granted by calling grantRole method in the contract on public chain. The first parameter is the value of PREDICATE_ROLE constant which is 0x12ff340d0cd9c652c747ca35727e68c547d0f0bfa7758d2e77f75acef481b4f2, and the second parameter is the corresponding address of MintableERC20PredicateProxy or MintableERC721PredicateProxy shown in the list below.

Public ChainContract NameContract Address
TRON MainnetMintableERC20PredicateProxyTH6JAd7DNka8Q6oKqkQMWJ6TYdLG6fQ6Kv
MintableERC721PredicateProxyTEHTjbuQfiJsTb2UdKHjMgmFGwLDqVDNh5
NILE TestnetMintableERC20PredicateProxyTUFWVA7fDHhvURrdNm9PS9mCPqx6T7mEPm
MintableERC721PredicateProxyTNvb1f4dCTsM6WwYQAPfmkqeLg8XcDCBzG
Ethereum MainnetMintableERC20PredicateProxy0x9277a463a508f45115fdeaf22ffeda1b16352433
MintableERC721PredicateProxy0xb932da3a1b3cba3f744edbc55cc1107575c37b6c
Goerli TestnetMintableERC20PredicateProxy0x5af2bca15245d534ede87a03c007852e055d4b87
MintableERC721PredicateProxy0xd769079211b69d6cf2e972d480a3809cd0103403
BSC MainnetMintableERC20PredicateProxy0xca266910d92a313e5f9eb1affc462bcbb7d9c4a9
MintableERC721PredicateProxy0x5b0effa5ba0286cfc099724f8df6261215c596f5
BSC TestnetMintableERC20PredicateProxy0x5f32098ca8b566f86b09a33e3b13e0da4a58c6c8
MintableERC721PredicateProxy0x9f5684dc39496a9e56114ebf63b7b108df4567b0

3. Submit Mapping Request​

In the end, please verify the child token contract on Bttcscan, and token contract on Tronscan/Ethscan/Bscscan respectivily, and submit mapping request here.