Using the MMC0 bus instead of MMC1 on roadrunner

This article illustrates how to boot and run Linux from a microSD card wired on MMC0 bus instead on MMC1

Wirings

There are the wirings between the Roadrunner module and a microSD/miniSD or SD card

CPU lines	SD signals	SD pin	uSD pin
PA0	CLK	5	5
PA1	CMD	2	3
PA2	DATA 0	7	7
PA3	DATA 1	8	8
PA4	DATA 2	9	1
PA5	DATA 3	1	2
	VCC	4	4
	GND	3,6	6
PA13 (*)	CD

(*) The PA13 line must be wired on CD (Carrier detect) line if your microSD socket has this pin or fixed on GND if not.

A 68 kOhm pull-up resistor must be wired on each of these lines:

DATA 0
DATA 1
DATA 2
DATA 3
CMD

Device tree binding

This is the device tree definition to use:

ahb {

    ...

    sdmmc0: sdio-host@a0000000 {
        bus-width = <4>;
        pinctrl-names = "default";
        no-1-8-v;
        non-removable;  
        pinctrl-0 = <&pinctrl_sdmmc0_default>;
        status = "okay";
    };

    sdmmc1: sdio-host@b0000000 {
        bus-width = <4>;
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_sdmmc1_default>;
    };

    ...


    apb {

        ...

        pinctrl_sdmmc0_default: sdmmc0_default {
            cmd_data {
                pinmux = <PIN_PA1__SDMMC0_CMD>,
                     <PIN_PA2__SDMMC0_DAT0>,
                     <PIN_PA3__SDMMC0_DAT1>,
                     <PIN_PA4__SDMMC0_DAT2>,
                     <PIN_PA5__SDMMC0_DAT3>;
                bias-disable;
            };

            ck_cd_rstn_vddsel {
                pinmux = <PIN_PA0__SDMMC0_CK>,
                     <PIN_PA13__SDMMC0_CD>;
                bias-disable;
            };
        };

        ...


    };

    ...


};

at91bootstrap config

To be compatible with boot from MMC0, at91bootstrap must be compiled with these flags configured inside the make menuconfig command (read Compiling AT91bootstrap 3.9.1)

Memory selection  --->
  Flash Memory Technology (SD card)  --->
    ( ) Dataflash
    (X) SD card

and

Memory selection  --->
    SD Card Configuration  --->
        SD Host Controller Select (On SDHC0)  --->
            (X) On SDHC0
            ( ) On SDHC1

Using the MMC0 bus instead of MMC1 on roadrunner

Wirings

Device tree binding

at91bootstrap config

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