http://www.pjrc.com/teensy/td_libs_SPI.html

This is an experimental fork with optimizations for teensy 4.x boards that adds a DMA-based transfer for FreeRTOS:

template <SPITransferType T> bool transfer_os(const T* txBuffer, T* rxBuffer, size_t count)

See github.com/PaulStoffregen/SPI for the original version.