MMC (MultiMediaCard) and SD (Secure Digital) are common storage devices that are widely used in embedded systems and mobile devices. In the Linux operating system, the MMC and SD subsystems are responsible for managing and driving these storage devices. This article will introduce the MMC and SD subsystems in the Linux device model in detail and provide corresponding source code examples.
Overview of the MMC and SD subsystems
The MMC and SD subsystems provide functions for accessing and managing MMC and SD storage devices. They implement read and write operations on storage devices by interacting with the device driver and block layer. The MMC and SD subsystems are responsible for handling the physical interface communication with the storage device and providing high-level abstract interfaces for use by applications.
MMC subsystem
The MMC subsystem is used to manage and drive MMC storage devices. It provides the implementation of the MMC protocol, including card initialization, command transmission, data transmission and other functions. The MMC subsystem exposes the properties and status of the MMC device through the sysfs interface, allowing user space programs to configure and monitor it.
The following is a simple example that demonstrates how to use the MMC subsystem in Linux to read the contents of an MMC storage device:
#include <linux/mmc/core.h>
#include <linux/mmc/host.h>