AXEL ULite SOM/DESK-MX6UL-L/Pheripherals/SD

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Version Issue Date Notes
1.0.0 Apr 2021 First DESK 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-lynx-som0013.dtsi:

&usdhc1 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_usdhc1>;
        cd-gpios = <&gpio1 19 GPIO_ACTIVE_LOW>;
        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     /* SD2 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.:

[    3.656628] sdhci-esdhc-imx 2190000.usdhc: Got CD GPIO
[    3.723545] mmc0: SDHCI controller on 2190000.usdhc [2190000.usdhc] using ADMA
[    3.781083] mmc0: host does not support reading read-only switch, assuming write-enable
[    3.795391] mmc0: new high speed SDHC card at address 59b4
[    3.802522] mmcblk0: mmc0:59b4 USDU1 14.9 GiB
[    3.819777]  mmcblk0: p1 p2
[    3.883026] mmc1: SDHCI controller on 2194000.usdhc [2194000.usdhc] using ADMA
[    5.270986] EXT4-fs (mmcblk0p2): mounting ext3 file system using the ext4 subsystem
[    5.335083] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. Opts: (null)...
[    4.857362] EXT4-fs (mmcblk0p2): mounting ext3 file system using the ext4 subsystem
[    4.877965] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. 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
[  699.148927] FAT-fs (mmcblk0p1): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.

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