01-11-2016, 05:01 PM
(01-11-2016, 02:09 PM)tllim Wrote:(01-11-2016, 08:28 AM)monmoonmooonmoooon Wrote: @@tllim
Can you enlight us please?
What will be the true speeds for SDCards? For example a support a Class 10 UHS-I in full speeds?
I have not fully try out the SD Cards speed. I knows that the A64 can handles SDXC and per datasheet, it accepts UHS command set. There are only few ARM SoC chips in market that support SDXC. From reading the A64 datasheet, my guess is A64 may able up to 50MB/s, but not 104MB/s which required lower 1.8v SD card. However, my assumption can be dead wrong. Once somebody bring up the Linux build, we can try out.
SDXC is a card standard, and has nothing to do with the interface. The ONLY way for ANY kernel, be it Linux or Android, to get beyond 25MB/s is to implement UHS, and this requires several things. A post by the makers of Rasperry Pi in their forums explains this is more detail.
"The Pi uses SD High-speed mode (SDR50) at 25MB/s - the option to use SDR104 or DDR50 exists but is not tested.
There are additional constraints on using these modes: the VDDIO voltage must be switched at runtime between 3.3V and 1.8V and the delay between card and host has to be tuned via a tuning register to match the PCB layout/card delay etc.
Even if you had a voltage switch available for the bank voltage select (Pi is hardwired to 3v3 for SD spec, compute module is wired to 1v8 for eMMC spec) I believe the kernel SDHCI driver currently does not implement this functionality therefore SDR104/DDR50 don't work. That and the hardware's not been tested at that speed - which is pushing it as far as the GPIO pad drivers can go - so the chances of success, even if you could hack the hardware to select the voltage, are slim."
