Snapper 9260 includes two MCI peripherals, allowing for connectivity to MMC, SD and SDIO devices. In this application note we discuss connecting an SD header to the MCI slot B, and then using this to access an SD storage card.
Note: This application note deals only with the core SD signals, and does not cover the write-protect, Vcc-enable, or card detect signals that are also commonly used.
SD Standard
SD storage cards can operate in two modes, SD or SPI. SPI mode is typically used for microcontrollers with fewer resources, as it is an easier bus to implement. It is however limited in speed, and unsuitable for SDIO devices. Snapper 9260 can operate SD cards in either mode, and as such full SD mode is generally preferred. This document discusses full SD mode.
SD cards have the following standard pin-out
| Pin | SD Mode | SPI Mode | ||||
|---|---|---|---|---|---|---|
| Name | Type | Description | Name | Type | Description | |
| 1 | CD/DAT3 | I/O/PP | Card detection / Data Line 3 | CS | I | Chip select |
| 2 | CMD | PP | Command/Response line | DI | I | Data input |
| 3 | GND | S | Ground | GND | S | Ground |
| 4 | Vcc | S | Power Supply | Vcc | S | Power Supply |
| 5 | CLK | I | Clock | SCLK | I | Clock |
| 6 | GND | S | Ground | GND | S | Ground |
| 7 | DAT0 | I/O/PP | Data Line 0 | DO | O/PP | Data output |
| 8 | DAT1 | I/O/PP | Data Line 1 | - | - | - |
| 9 | DAT2 | I/O/PP | Data Line 2 | - | - | - |
QSK Connection
To attach an SD socket to the Snapper 9260 QuickStart Kit, use the following connections
| SD Pin | Name | QSK Pin | GPIO | Snapper 9260 Pin |
|---|---|---|---|---|
| 1 | CD/DAT3 | 53 | PA3 | 69 |
| 2 | CMD | 45 | PA1 | 61 |
| 3 | GND | 57 | - | - |
| 4 | Vcc | 58 | - | - |
| 5 | CLK | 43 | PA8 | 59 |
| 6 | GND | 59 | - | - |
| 7 | DAT0 | 47 | PA0 | 63 |
| 8 | DAT1 | 49 | PA5 | 65 |
| 9 | DAT2 | 51 | PA4 | 67 |
Linux Software
Once the hardware has been correctly attached, the Linux kernel must be rebuilt to include support for SD cards.
- Make the following changes to arch/arm/mach-at91rm9200/board-snapper9260.c
- Add an mmc_data structure definition:
/*
* MCI (SD/MMC)
*/
static struct at91_mmc_data __initdata mmc_data = {
.slot_b = 1,
.wire4 = 1,
};
-
- Initialise the MMC subsystem (inside sn9260_board_init)
at91_add_device_mmc(&mmc_data);
- Rebuild kernel with the following config options enabled
CONFIG_MMC=y CONFIG_MMC_BLOCK=y CONFIG_MMC_AT91=y
- Update the kernel on the Snapper 9260, either in the on-board NAND flash, or by booting the unit over the network.
- When the SD device is detected, output similar to the following will be displayed on the serial console:
mmcblk0: mmc0:0001 SD 1964544KiB mmcblk0: p1
- Once detected, the SD card can be mounted and used as a standard Linux block device
root@snapper:~$ mount /dev/mmcblk0p1 /mnt/ root@snapper:~$ cp my_file /mnt root@snapper:~$ ls /mnt my_file root@snapper:~$ umount /mnt/
Snapper 9260 includes two MCI peripherals, allowing for connectivity to MMC, SD and SDIO devices. In this application note we discuss connecting an SD header to the MCI slot B, and then using this to access an SD storage card.
Note: This application note deals only with the core SD signals, and does not cover the write-protect, Vcc-enable, or card detect signals that are also commonly used.
