How is an HD Wallet Key Generated?

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Please help me understand how you generate a Private key + Chaincode from entropy.

As I understand it, you generate entropy which should be random and can vary from 128 – 256 bits of data. You could use a coin or dice for this purpose.

Then you generate the checksum; in the case of 12 words it will be 4 bits, therefore 132 bits in total. Next, you take 132 bits and run it through PBKDF2 with HMAC-SHA512 2048 times with a string "mnemonic" + optional passphrase.

You receive 512 bits of data, called the Seed. Afterwards, you put the 512 bit seed through HMAC-SHA512 with "Bitcoin seed" and you receive 512 bits of data which is split into the private key and the chain code.

The part I don’t understand is that some sources say you put the Seed which can be 128, 256 or 512 bits in length through the HMAC-SHA512 to get the private key and the chaincode. How is it possible if the Seed should be 512 bits in length?

In the picture below, it is named Root Seed.

My understanding is that it works like this. The first picture is from Mastering Bitcoin, the other from learnmeabitcoin.com