UHS-I support on Sabrelite board.

[zaheerm]

Hi,

We are using a Sabrelite board (i.MX6Q) with 3.0.35 kernel. The host supports UHS-I SDR 50 and 104 modes. However when we plug in a UHS-I SD card to usdhc3, we see that it gets detected as a "High speed device" rather than a 'ultra high speed device'. Browsing through the sources, we found that to for the SD card to work in UHS mode, the host needs to switch to 1.8v from 3.3v.

Looks like Sabrelite does not support this voltage level and hence restricts this switch over. The result being that though there is a UHS SD card its get detected as a high-speed device, also limiting the data throughput rates.

Is this understanding correct? Has anyone come across a similar scenario?

Any pointers to enable the UHS-I support will be helpful.

Regards,

Zaheer.

[EricNelson · Accepted solution]

Hi Zaheer,

Your understanding is exactly right.

At the moment, none of our boards supports voltage switching of the SD card I/O, and that's a pre-requisite for UHS speeds.

[zaheerm]

Hi Eric,

Thanks for the conformation.

The second confusion is that, we measured the Clock speed on uSDHC3 and found it to be 50 MHz.We ran the throughput tests using tools like 'Bonnie', and found block write speeds of 65MBps and block read speeds of 70 MBps. The SD specification says that in High-speed mode the max bus speed can be 25 MB/s.

Am i missing something here?

Regards,

Zaheer.

[EricNelson]

Hi Zaheer,

I think you're missing that the 50MHz bus is 4 bits wide, so the nominal bit rate is 200Mbits/s.

In practice we see ~20MBytes/s throughput performing block reads (less for files because of filesystem overhead).

[zaheerm]

HI,

I would like to know if any one has tested UHS SDR 104 mode on any of iMX6 platform.

Regards,

zaheer