# Using the MMC0 bus instead of MMC1 on roadrunner

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

## 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


<img src="./sdpins.png" width="290px">

## 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 @article='at91bootstrap')
	
	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


@include='adv_roadrunner'