DDR200 on the Framework MicroSD Expansion Card

The_Official_GMan · November 28, 2023, 6:58pm

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

github.com/CTCaer/switch-l4t-kernel-4.9

mmc: sdhci: add UHS DDR200 support

committed 07:19AM - 31 Mar 23 UTC

CTCaer

+82 -15

SD Card UHS DDR200 (DDR208) support. Proper procedure: 1. Check that Vendor Spe…cific Command System is supported. Used as Enable DDR200 Bus. 2. Enable DDR200 bus mode via setting 14 to Group 2 via CMD6. Access Mode group is left to default 0 (SDR12). 3. Setup clock to 200 or 208 MHz. 4. Set host to DDR bus mode that supports such high clocks. Some hosts have special mode, others use DDR50 and others HS400 4-bit. 5. Execute hardware or software Tuning. The true validation that this value in Group 2 activates it, is that DDR50 bus and clocks/timings work fully after that point. All that simply works, because the DDR200 is simply SDR104 in DDR mode, so sampling on rising and falling edge and with variable output data window. It can be supported by any host that is fast enough to support DDR at 200/208MHz and can do hw/sw tuning for finding the proper sampling window in that mode. Signed-off-by: CTCaer <ctcaer@gmail.com>

github.com/CTCaer/switch-l4t-kernel-4.9

mmc: sdhci: tegra: add UHS DDR200 support

committed 07:34AM - 31 Mar 23 UTC

CTCaer

+226 -9

SD Card UHS DDR200 (DDR208) support. On all Tegra platforms, support can be add…ed via DDR50 host mode. Tuning though can't be done automatically on any DDR mode. So it needs to be done manually and selected tap will be applied from the biggest sampling window. Any platform to support it, must be able to withstand DDR at 400 MHz host clock. New Device Tree properties were added to support it: `enable-ddr200` actually enables that mode. `ddr200-clk-limit` fine-tunes the card clock (host is 2x that, 200 -> 400 MHz). `prod_c_ddr200` holds the prod settings. All 3 are mandatory to make it work. On platforms that dvfs is managed by BPMP, its own device tree must be changed in order to set max supported SDMMC host clock. Using a SDMMC controller on DDR200 mode at 400MHz, has latency allowance implications. The MC/EMC must be clocked enough to be able to serve the requests in time (512B in 1.28 ns). 800 MHz EMC clock and 400 MHz MC clock should be enough. Plus the latency allowance registers should be set to eMMC SDMMC values. Signed-off-by: CTCaer <ctcaer@gmail.com>

The samsung microSD to USB readers commonly sold bundled with these cards also support samsung’s DDR200 implementation.

voltagex · April 8, 2024, 2:57am

Hey @The_Official_GMan offtopic I guess, but do you know which SDXC chips (?) support DDR200? How can I find readers which support this?

The_Official_GMan · April 9, 2024, 7:02pm

@voltagex The samsung Pro Plus and Pro Ultimate SD cards are confirmed to support DDR200. The reader that samsung bundles with (some of) those officially also supported samsung’s implementation of DDR200.

The sandisk extreme A2 cards support DDR200 using sandisk’s original DDR200 implementation. A DLL mechanism is required for these cards otherwise they quickly drift and require frequent re-tuning. I can confirm that they work at DDR200 speed (using a driver without that DLL mechanism) which just results in frequent re-tuning and some stability issues. I do not know of any reader that is able to read these cards reliably, they do not work at DDR200 on the samsung reader. The sandisk SDDR-B531-GN6NN reader adversities read rates of up to 170MB/s over UHS-I so it must support DDR200 but I do not have any experience using it.

There are a LOT of other cards that advertise DDR200 support but I do not have experience with them. Any card that advertises either read or write performance exceeding 100MB/s and is a UHS-I card is a card that supports DDR200 via some reader.