DESK-MX6UL-L/Pheripherals/SD

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History
Version Issue Date Notes

1.0.0

Apr 2021 First DESK release
2.0.0 Feb 2022 DESK 3.0.0 release


Peripheral SD[edit | edit source]

Device tree configuration[edit | edit source]

Here below an example of device tree configuration used on standard DAVE's kit for the AXEL ULite SOM:

From imx6ul-axelulite.dtsi:

&usdhc1 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_usdhc1>;
        cd-gpios = <&gpio1 19 GPIO_ACTIVE_LOW>;
        bus-width = <4>;
        no-1-8-v;
        keep-power-in-suspend;
        enable-sdio-wakeup;
        status = "okay";
};
...
...
&iomuxc {
...
...
        pinctrl_usdhc1: usdhc1grp {
            fsl,pins = <
                MX6UL_PAD_SD1_CMD__USDHC1_CMD       0x17059
                MX6UL_PAD_SD1_CLK__USDHC1_CLK       0x10071
                MX6UL_PAD_SD1_DATA0__USDHC1_DATA0   0x17059
                MX6UL_PAD_SD1_DATA1__USDHC1_DATA1   0x17059
                MX6UL_PAD_SD1_DATA2__USDHC1_DATA2   0x17059
                MX6UL_PAD_SD1_DATA3__USDHC1_DATA3   0x17059
                MX6UL_PAD_UART1_RTS_B__GPIO1_IO19   0x17059     /* SD1 CD */
            >;
        };
...
...
};

The USDHC interface is re-configured on carrier device tree because of the Card Detect pin (which is related to the real board hardware implementation).

Accessing the peripheral[edit | edit source]

Once initialized, the SD device is mapped to the standard /dev/mmcblk0pX block device, depending on how many partition are created on the SD card.

Linux messages at boot time[edit | edit source]

If the microSd card is inserted at boot time, the kernel - once the USDHC interface has been initialized - prints the device information and the partition detected like p1, p2, etc.:

...
...
[    3.236168] mmc0: SDHCI controller on 2190000.mmc [2190000.mmc] using ADMA
[    3.308821] mmc0: host does not support reading read-only switch, assuming write-enable
[    3.328089] mmc0: new high speed SDHC card at address aaaa
[    3.346316] mmcblk0: mmc0:aaaa SL32G 29.7 GiB 
[    3.362682]  mmcblk0: p1 p2
[    4.482459] EXT4-fs (mmcblk0p2): recovery complete
[    4.498197] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. Opts: (null)
[    8.414331] EXT4-fs (mmcblk0p2): re-mounted. Opts: (null)
...
...

Additional information[edit | edit source]

If the root file system configuration does not automatically mount the partition, it is possible to mount the device using the following command:

root@desk-mx6ul-axelulite:~# mkdir -p /mnt/boot
root@desk-mx6ul-axelulite:~# mount /dev/mmcblk0p1 /mnt/boot/
root@desk-mx6ul-axelulite:~# ls /mnt/boot/
boot.scr  imx6ul-axelulite-cb003a.dtb  imx6ul-axelulite-cb006c.dtb  splash_image.bmp  uImage

and then the mounted partition is available on the /mnt/boot root file system directory.