Secure Digital High Capacity (SDHC)
The SDHC api offers a generic interface for interacting with an SD host controller device. It is used by the SD subsystem, and is not intended to be directly used by the application
Basic Operation
SD Host Controller
An SD host controller is a device capable of sending SD commands to an attached SD card. These commands can be sent using the native SD protocol, or over SPI. Some SD host controllers are also capable of communicating with MMC devices. The SDHC api is designed to provide a generic way to send commands to and interact with attached SD devices.
Requests
The core of the SDHC api is the sdhc_request() api. Requests contain a
sdhc_command command structure, and an optional
sdhc_data data structure. The caller may check the return code,
or the response field of the SD command structure to determine if the
SDHC request succeeded. The data structure allows the caller to specify a
number of blocks to transfer, and a buffer location to read or write them from.
Whether the provided buffer is used for sending or reading data depends on the
command opcode provided.
Host Controller I/O
The sdhc_set_io() api allows the user to change I/O settings of the SD
host controller, such as clock frequency, I/O voltage, and card power. Not all
controllers will support applying all I/O settings. For example, SPI mode
controllers typically cannot toggle power to the SD card.
Related configuration options: