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().
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
Disk Access API Configuration Options
Related configuration options:
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.
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
-
int disk_access_init(const char *pdrv)
Disk Driver Configuration Options
Related driver configuration options:
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_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
-
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.
-
sys_dnode_t node
-
struct disk_operations
- #include <disk.h>
Disk operations.