SD CARD PERFORMANCE/SPEED SLOW IMX6Q

valentinafernan — Thu, 23 Jul 2015 04:50:37 GMT

Hi,

We have a custom board based on IMX6 Sabre Auto. The board supports voltage switching from 3.3 V to 1.8 V using the VSELECT signal in the SD card interfaces. However, when inserting a Lexar 633x 128 GB microSD card and using the hdparm utility the output shows the following ( speed is too slow considering that SDR104 max bus speed is 104 MB/s) :

/dev/mmcblk2:

Timing cached reads: 656 MB in 2.00 seconds = 327.47 MB/sec

Timing buffered disk reads: 118 MB in 3.01 seconds = 39.18 MB/sec

We can confirm that the voltage is switching to 1.8V (measuring voltage) and that linux is identifying the microSD card as UHS SDR104 with the following test:

root@localhost:~# cat /sys/kernel/debug/mmc2/ios

clock: 198000000 Hz

actual clock: 198000000 Hz

vdd: 21 (3.3 ~ 3.4 V)

bus mode: 2 (push-pull)

chip select: 0 (don't care)

power mode: 2 (on)

bus width: 2 (4 bits)

timing spec: 6 (sd uhs SDR104)

signal voltage: 0 (1.80 V)

Why is the SD access speed so slow? We are using kernel 3.14.28

Thanks

Re: SD CARD PERFORMANCE/SPEED SLOW IMX6Q

Bio_TICFSL — Tue, 28 Jul 2015 13:38:49 GMT

Hi Valentina,

According to the MX6 RM http://cache.freescale.com/files/32bit/doc/data_sheet/IMX6DQCEC.pdf

section 4.11.4.3 shows AC Timmings for sDR50/SDR104

In 4bit mode, our SDXC speed can be up to 104mbps, It means 13MB/s. Also Lexar 128G is Class10 card supports above 10MB/S, So this type of card should normally work at this speed on I.MX6 platform.

Hope this helps

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SD CARD PERFORMANCE/SPEED SLOW IMX6Q

Re: SD CARD PERFORMANCE/SPEED SLOW IMX6Q