Many A2 MicroSD UHS-I cards support the UHS DDR200. Example of such a card are the Samsung Pro Plus and Pro Ultimate cards. This allows for up to nearly 200MB/s throughput on DDR200 from nearly 100MB/s throughput on SDR104.
On the original implementation of DDR200 from Sandisk, a DLL mechanism, like the one in eMMC HS400 is mandatory. So the card can start data signals whenever it wants, and the host should synchronize to the first DAT signal edge change. Every single other vendor that implemented DDR200, always starts data transfers aligned to clock. That basically makes DDR200 in such SD cards a SDR104 but sampled on both edges. So effectively, it’s an in-spec signal with DDR50, only that is clocked at 200MHz, instead of 50MHz. So the extra needed thing is using a tuning window, which is absent from the original implementation, since DDL syncing does not use that.
Given that SDR100 already functions and DDR200 uses the same clockspeed (200-208 Mhz) this should be possible on most readers.
I would like for this feature (DDR200) to be added to the framework MicroSD card reader as the switchroot group did for the tegra sdhci
The samsung microSD to USB readers commonly sold bundled with these cards also support samsung’s DDR200 implementation.