The TF-PSA-Crypto repository contains two maintained branches:
The development of the TF-PSA-Crypto repository code occurs on the development branch. No cryptography code development occurs on this branch though. The development branch just contains a framework, a CMake build system and scripts to integrate the Mbed TLS implementation of the PSA cryptography API into this repository. The main branch commits are the results of such integrations (see docs/architecture/tf-psa-crypto-repository.md for more information).
The TF-PSA-Crypto repository provides an implementation of the PSA cryptography API through its main branch. The main branch is updated regularly against the head of the Mbed TLS development branch.