Disk Access

Overview

The disk access API provides access to storage devices.

Initializing Disks

Since many disk devices (such as SD cards) are hotpluggable, the disk access API provides IOCTLs to initialize and de-initialize the disk. They are as follows:

DISK_IOCTL_CTRL_INIT: Initialize the disk. Must be called before additional I/O operations can be run on the disk device. Equivalent to calling the legacy function disk_access_init().
DISK_IOCTL_CTRL_DEINIT: De-initialize the disk. Once this IOCTL is issued, the DISK_IOCTL_CTRL_INIT must be issued before the disk can be used for addition I/O operations.

Init/deinit IOCTL calls are balanced, so a disk will not de-initialize until an equal number of deinit IOCTLs have been issued as init IOCTLs.

It is also possible to force a disk de-initialization by passing a pointer to a boolean set to true as a parameter to the DISK_IOCTL_CTRL_DEINIT IOCTL. This is an unsafe operation which each disk driver may handle differently, but it will always return a value indicating success.

Note that de-initializing a disk is a low level operation- typically the de-initialization and initialization calls should be left to the filesystem implementation, and the user application should not need to manually de-initialize the disk and can instead call fs_unmount()

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

FAT filesystems are not power safe so the filesystem may become corrupted if power is lost or if the card is removed without unmounting the filesystem

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().

eMMC Device Support

Zephyr also has support for eMMC devices using the Disk Access API. MMC in zephyr is implemented using the SD subsystem because the MMC bus shares a lot of similarity with the SD bus. MMC controllers also use the SDHC device driver API.

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.

NVMe disk support

NVMe disks are also supported

NVMe

Disk Access API Configuration Options

Related configuration options:

CONFIG_DISK_ACCESS

API Reference

Related code samples

File system manipulation: Use file system API with various filesystems and storage devices.

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. Although still supported for legacy compatibility, users should instead call disk_access_ioctl with the IOCTL DISK_IOCTL_CTRL_INIT.

Disk initialization is reference counted, so only the first successful call to initialize a uninitialized (or previously de-initialized) disk will actually initialize the disk

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.

Note: if he disk is of NVMe type, user will need to ensure data_buf pointer is 4-bytes aligned.

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.

Note: if he disk is of NVMe type, user will need to ensure data_buf pointer is 4-bytes aligned.

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.

Since: 1.6
Version: 1.0.0

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_IOCTL_CTRL_INIT

Initialize the disk.

This IOCTL must be issued before the disk can be used for I/O. It is reference counted, so only the first successful invocation of this macro on an uninitialized disk will initialize the IO device

DISK_IOCTL_CTRL_DEINIT

Deinitialize the disk.

This IOCTL can be used to de-initialize the disk, enabling it to be removed from the system if the disk is hot-pluggable. Disk usage is reference counted, so for a given disk the DISK_IOCTL_CTRL_DEINIT IOCTL must be issued as many times as the DISK_IOCTL_CTRL_INIT IOCTL was issued in order to de-initialize it.

This macro optionally accepts a pointer to a boolean as the buf parameter, which if true indicates the disk should be forcibly stopped, ignoring all reference counts. The disk driver must report success if a forced stop is requested, but this operation is inherently unsafe.

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.

const char *name: Disk name.

const struct disk_operations *ops: Disk operations.

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

uint16_t refcnt: Internally used disk reference count.

struct disk_operations: #include <disk.h>

Disk operations.