Linux (Open Source) SD/MMC/sdio support current situation Overview

From: http://www.jollen.org/blog/2007/01/open_source_sd_mmc_sdio.html

SD (Secure Digital) and MMC (multimedia card)

SD is a standard for flash memory card, which is a common SD memory card, while MMC is an early memory card, SD
Replaced by standard. According to the SD/MMC specification of zookeeper, [http://zh.wikipedia.org/wiki/secure_digital=.

Sdio (Secure Digital I/O)

Sdio is a technology that is more important to us at present. sdio is a well-known concept, that is, sd I/O
Interface (Interface), but this solution may be a bit of image. More specifically, SD is the title of the memory card, but now we can also
In this way, we can plug in some zookeeper interfaces for use. This is sdio.

Therefore, sdio itself is a simple technique. It uses sd I/O to access external audio, and the I/O data location on the SD is connected to these dynamic resources, and the SD
The Conference members also launched a complete sdio stack notebook program, making the development and application of sdio audio program (we think sdio card) Quite simple.

Nowadays, many mobile phones or handheld devices support the sdio function (the SD standard was originally set for mobile devices), and many sdio
All the hosts are also developed to make it easier for external hosts on the mobile phone and make the development more efficient (internal memory creation is not required ). Common sdio audio cards are:

• Wi-fi card (unlimited network card)
• CMOS sensor card (photo module)
• GPS card
• GSM/GPRS modem card
• Bluetooth card
• Radio/TV card (fun)

The Application of sdio will be one of the most important interfaces of embedded systems in the future, and will also replace the current gpio-type SPI interface.

Zookeeper mode of SD/sdio

The following three modes are available:

• SPI mode (required)
• 1-Bit mode
• 4-Bit mode

Sdio also supports the above three zookeeper modes. According to the SD standard, all SD and sdio must support the SPI mode, so the SPI Mode
Is "required 」. In addition, early MMC cards (using SPI trunk cable) can also be connected to SD slots and use SPI mode or 1-bit
Mode.

Sd mmc Mode

SD can also capture the MMC memory, although the MMC Mark says that the MMC memory does not necessarily support SPI mode (but must support 1-bit ).
Mode), but the MMC cards available in the market all support SPI mode. Therefore, we can set SD to the callback mode of SPI mode to retrieve MMC.
Memory card.

Sd mmc mode is a memory mode used to fetch the MMC card. However, sd mmc mode uses SPI.
Mode, but its physical characteristics are still poor:

• The maximum memory usage rate of mmc spi mode is 20 Mbit/s;
• The maximum latency of sd spi mode is 25 Mbit/s.

To avoid confusion, we also use the classification method of SPI/MMC mode and SPI/SD mode to clarify the differences.

Linux SD/MMC drivers

Linux 2.6.17 officially joins the SD/MMC mobile program. The "official version" release can only be used on the ARM platform.
Controller support. Currently, Linux SD/MMC/sdio supports the following kernel APIs (Open Source compatible ):
SD/MMC/sdio ):

1. Support for MMC. The practice of open source is the notebook of the SD-MMC.

2. core API supports SD/SPI ModeOnlyBecause there is a routing method to support SPI mode, of course, 1-Bit mode
Also, you can refer to the suggestion method. 1-Bit mode is recharged to 4-Bit mode, but some people do it on the network, but there will be copyright issues.

3. Currently, sdio only supports the atheros Wi-fi card (which can be found on SourceForge and has been released
Code ).

4. Complete SD stack payment is required. Please note that SD Card Association Product License Agreement
And "no" allows the Open Source Operation to be implemented. So there is no need to ask why there is no open source SD actuator; Linux
No sin!

Please note that the above is the official support provided by the "official" and does not include various patches shared by players.