Disk Access

Overview

The disk access API provides access to storage devices.

SD Card support

Zephyr has support for some SD card controllers and support for interfacing SD cards via SPI. These drivers use disk driver interface and a file system can access the SD cards via disk access API. Both standard and high-capacity SD cards are supported.

Note

The system does not support inserting or removing cards while the system is running. The cards must be present at boot and must not be removed. This may be fixed in future releases.

FAT filesystems are not power safe so the filesystem may become corrupted if power is lost or if the card is removed.

SD Memory Card subsystem

Zephyr supports SD memory cards via the disk driver API, or via the SDMMC subsystem. This subsystem can be used transparently via the disk driver API, but also supports direct block level access to cards. The SDMMC subsystem interacts with the sd host controller api to communicate with attached SD cards.

SD Card support via SPI

Example devicetree fragment below shows how to add SD card node to spi1 interface. Example uses pin PA27 for chip select, and runs the SPI bus at 24 MHz once the SD card has been initialized:

&spi1 {
        status = "okay";
        cs-gpios = <&porta 27 GPIO_ACTIVE_LOW>;

        sdhc0: sdhc@0 {
                compatible = "zephyr,sdhc-spi-slot";
                reg = <0>;
                status = "okay";
                mmc {
                    compatible = "zephyr,sdmmc-disk";
                    status = "okay";
                };
                spi-max-frequency = <24000000>;
        };
};

The SD card will be automatically detected and initialized by the filesystem driver when the board boots.

To read and write files and directories, see the File Systems in include/zephyr/fs/fs.h such as fs_open(), fs_read(), and fs_write().

Emulated block device on flash partition support

Zephyr flashdisk driver makes it possible to use flash memory partition as a block device. The flashdisk instances are defined in devicetree:

/ {
    msc_disk0 {
        compatible = "zephyr,flash-disk";
        partition = <&storage_partition>;
        disk-name = "NAND";
        cache-size = <4096>;
    };
};

The cache size specified in zephyr,flash-disk node should be equal to backing partition minimum erasable block size.

Disk Access API Configuration Options

Related configuration options:

CONFIG_DISK_ACCESS

API Reference

group disk_access_interface

Disk Access APIs.

Functions

int disk_access_init(const char *pdrv)

perform any initialization

This call is made by the consumer before doing any IO calls so that the disk or the backing device can do any initialization.

Parameters

pdrv – [in] Disk name

Returns

0 on success, negative errno code on fail

int disk_access_status(const char *pdrv)

Get the status of disk.

This call is used to get the status of the disk

Parameters

pdrv – [in] Disk name

Returns

DISK_STATUS_OK or other DISK_STATUS_*s

int disk_access_read(const char *pdrv, uint8_t *data_buf, uint32_t start_sector, uint32_t num_sector)

read data from disk

Function to read data from disk to a memory buffer.

Parameters

pdrv – [in] Disk name
data_buf – [in] Pointer to the memory buffer to put data.
start_sector – [in] Start disk sector to read from
num_sector – [in] Number of disk sectors to read

Returns

0 on success, negative errno code on fail

int disk_access_write(const char *pdrv, const uint8_t *data_buf, uint32_t start_sector, uint32_t num_sector)

write data to disk

Function write data from memory buffer to disk.

Parameters

pdrv – [in] Disk name
data_buf – [in] Pointer to the memory buffer
start_sector – [in] Start disk sector to write to
num_sector – [in] Number of disk sectors to write

Returns

0 on success, negative errno code on fail

int disk_access_ioctl(const char *pdrv, uint8_t cmd, void *buff)

Get/Configure disk parameters.

Function to get disk parameters and make any special device requests.

Parameters

pdrv – [in] Disk name
cmd – [in] DISK_IOCTL_* code describing the request
buff – [in] Command data buffer

Returns

0 on success, negative errno code on fail

Disk Driver Configuration Options

Related driver configuration options:

CONFIG_DISK_DRIVERS

Disk Driver Interface

group disk_driver_interface

Disk Driver Interface.

Defines

DISK_IOCTL_GET_SECTOR_COUNT

Possible Cmd Codes for disk_ioctl()

Get the number of sectors in the disk

DISK_IOCTL_GET_SECTOR_SIZE: Get the size of a disk SECTOR in bytes

DISK_IOCTL_RESERVED: reserved. It used to be DISK_IOCTL_GET_DISK_SIZE

DISK_IOCTL_GET_ERASE_BLOCK_SZ: How many sectors constitute a FLASH Erase block

DISK_IOCTL_CTRL_SYNC: Commit any cached read/writes to disk

DISK_STATUS_OK

Possible return bitmasks for disk_status()

Disk status okay

DISK_STATUS_UNINIT: Disk status uninitialized

DISK_STATUS_NOMEDIA: Disk status no media

DISK_STATUS_WR_PROTECT: Disk status write protected

Functions

int disk_access_register(struct disk_info *disk)

Register disk.

Parameters

disk – [in] Pointer to the disk info structure

Returns

0 on success, negative errno code on fail

int disk_access_unregister(struct disk_info *disk)

Unregister disk.

Parameters

disk – [in] Pointer to the disk info structure

Returns

0 on success, negative errno code on fail

struct disk_info

#include <disk.h>

Disk info.

Public Members

sys_dnode_t node: Internally used list node

char *name: Disk name

const struct disk_operations *ops: Disk operations

const struct device *dev: Device associated to this disk

struct disk_operations: #include <disk.h>

Disk operations.