http://libre-riscv.org/shakti/m_class/sdmmc/
talking to rudolf of asics.ws about updating the specs on sd/mmc to eMMC performance level. may need a PCB to be designed and made up in order to test it. could potentially be done as a break-out board?
tracked down JESD84-B51 eMMC 5.1 standard (register on jedec.org) also need to get hold of sdcard.org SDIO full standard for rudolf.
$25k to rudi, 6 months for completion (estimated).
https://github.com/mczerski/SD-card-controller