The Pico RMII Ethernet library, Neon Chrome Edition (NCE) is an update to the existing library by Sandeep Mistry, showcasing improved performance when Pico is overclocked to 300 MHz, achieving 94.9 Mbit/sec as tested by iperf. The library offers greater flexibility in choosing system clocks and uses DMA-driven ring buffers for both transmit and receive. Notably, the MDIO interface has been changed to interrupt-driven, freeing up processor time for packet processing. However, for optimal performance, the library must be run directly from RP2040 SRAM. Sandeep Mistry is acknowledged for the discovery that using an external clock for the RMII board significantly enhances performance.
https://github.com/rscott2049/pico-rmii-ethernet_nce