Multimedia Card Interface (MMC/SD) Driver

Name

Multimedia Card Interface (MMC/SD) Driver -- Using MMC/SD cards with block drivers and filesystems

Overview

The MultiMedia Card Interface (MMC/SD) driver in the OMAP processor HAL allows use of MultiMedia Cards (MMC cards) and Secure Digital (SD) flash storage cards within eCos, exported as block devices. This makes them suitable for use as the underlying devices for filesystems such as FAT.

Configuration

This driver provides the necessary support for the generic MMC bus layer within the CYGPKG_DEVS_DISK_MMC package to export a disk block device. The disk block device is only available if the generic disk I/O layer found in the package CYGPKG_IO_DISK is included in the configuration.

The block device may then be used as the device layer for a filesystem such as FAT. Example devices are "/dev/mmcsd0/1" to refer to the first partition on the card, or "/dev/mmcsd0/0" to address the whole device including potentially the partition table at the start.

The driver may be forcibly disabled within this processor HAL package with the configuration option CYGPKG_HAL_ARM_ARM9_OMAP_L1XX_MMC.

If the driver is enabled, the following options are available to control it:

CYGPKG_HAL_ARM_ARM9_OMAP_L1XX_MMC_DEVICE

The OMAP_L1XX has two MMC/SD devices. At present the generic MMC/SD code can only handle one device. This option selects which device that is.

CYGIMP_HAL_ARM_ARM9_OMAP_L1XX_MMC_INTMODE

This indicates that the driver should operate in interrupt-driven mode if possible. This is enabled by default if the eCos kernel is enabled. Note though that if the driver finds that global interrupts are off when running, then it will fall back to polled mode even if this option is enabled. This allows for use of the MMC/SD driver in an initialisation context.

CYGNUM_HAL_ARM_ARM9_OMAP_L1XX_MMC_INT_PRI

This is the MMC/SD bus interrupt priority. It may range from 1 to 29.

Usage Notes

The driver will detect the appropriate card sizes. Hotswapping of cards is supported by the driver, and in the case of eCosPro, the FAT filesystem. Although any cards removed before explicit unmounting or a sync() call to flush filesystem buffers will likely result in a corrupted filesystem on the removed card.

The MMC/SD bus layer will parse partition tables, although it can be configured to allow handling of cards with no partition table.

This driver implements multi-sector I/O operations. If you are using the FAT filesystem, see the generic MMC/SD driver documentation which describes how to exploit this feature when using FAT.

2017-02-09
Documentation license for this page: eCosPro License