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i.MX6UL USDHC2: Unexpected behaviour of CMD line

Question asked by Philipp Bachmann on May 23, 2018
Latest reply on May 24, 2018 by Philipp Bachmann



We want to connect the Murata LBEE5KL1DX-TEMP-DS-SD EVK with a non-NXP evaluation kit based on the i.MX6UL, the phyBoard-Segin by Phytec (i.MX 6UL NXP ARM Cortex-A7 Single Board Computer | PHYTEC ). I've downloaded their yocto environment for the BSP-Yocto-Vendor-phyBOARD-Segin-PD17.1.2 based on NXP Tag rel_imx_4.1.15_2.1.0_ga (


I adjusted my device tree according to the imx6ul EVK device tree "imx6ul-evk-btwifi.dtsi" to connect module on SD2 interface. My device tree is added at the end. During boot up the board seems to apply my changes:


[    1.749979] /soc/aips-bus@02100000/usdhc@02194000: voltage-ranges unspecified
[    1.760376] sdhci-esdhc-imx 2194000.usdhc: could not get ultra high speed state, work on normal mode
[    1.769805] sdhci-esdhc-imx 2194000.usdhc: assigned as wifi host
[    1.780510] sdhci-esdhc-imx 2194000.usdhc: No vmmc regulator found
[    1.788909] sdhci-esdhc-imx 2194000.usdhc: No vqmmc regulator found
[    1.833352] mmc0: host does not support reading read-only switch, assuming write-enable
[    1.842911] mmc1: SDHCI controller on 2194000.usdhc [2194000.usdhc] using ADMA
[    1.854506] mmc0: new high speed SDHC card at address 59b4



However, the module is not recognized. I measured the signals with and without the wifi module connected: VCC and WL_REG_ON are both ok. The CLK line is also fine, but the CMD line shows a weird behaviour. I've attached an image showing signals during boot (sorry for the low quality). Yellow is CLK, blue is CMD and purple is DATA0. During transmission the CMD line seems fine but before and after that it stays at around 0.6V. In my opinion the line should go back high to 3.3V.


When decrypting the pad characteristics of the CMD pin in the device tree, the value 0x17059 shows that 47k pull-up and CMOS output is enabled. But even when I attach an external 47k pull-up to VCC the CMD line does not go back high.


Can anybody help me with this problem?


Thanks and regards




My device tree:



/ {
    regulators {
        reg_wlan_en: regulator@100 {
            compatible = "regulator-fixed";
            regulator-name = "wlan_en";
            regulator-min-microvolt = <3300000>;
            regulator-max-microvolt = <3300000>;
            gpio = <&gpio5 9 GPIO_ACTIVE_HIGH>;
            startup-delay-us = <100>; /* card specific delay */
            status = "okay";


    bcmdhd_wlan_0: bcmdhd_wlan@0 {
        compatible = "android,bcmdhd_wlan";
        wlreg_on-supply = <&reg_wlan_en>;
        gpios = <&gpio1 3 0>; //wifi_wake_host


&iomuxc {
    imx6ul-phytec-peb-wlbt-01 {
        pinctrl_usdhc2_wlan: usdhc2grp_wlan {
            fsl,pins = <
                MX6UL_PAD_LCD_DATA18__USDHC2_CMD       0x17059
                MX6UL_PAD_LCD_DATA19__USDHC2_CLK         0x10059
                MX6UL_PAD_LCD_DATA20__USDHC2_DATA0    0x17059
                MX6UL_PAD_LCD_DATA21__USDHC2_DATA1    0x17059
                MX6UL_PAD_LCD_DATA22__USDHC2_DATA2    0x17059
                MX6UL_PAD_LCD_DATA23__USDHC2_DATA3    0x17059


        pinctrl_wlan: wlangrp {
            fsl,pins = <
                /* WLAN ENABLE */
                MX6UL_PAD_SNVS_TAMPER9__GPIO5_IO09    0x80000000
                /* WLAN IRQ */
                MX6UL_PAD_GPIO1_IO03__GPIO1_IO03    0x80000000


/* SDHC2 on phyBOARD-Segin i.MX6UL */
&usdhc2 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_usdhc2_wlan>;
    wifi-host; /* add hook for SD card detect mechanism for BCMDHD driver */

    status = "okay";