Power On and Off Notifications for Secure Digital Card Drivers
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8/28/2008
Within the Secure Digital (SD) card bus architecture, the host controller driver has the option of removing slot power when the OS is suspended.
The removal of the device instance for a slot cannot occur until the OS returns from the suspend state. When the system returns from the suspend state, the host controller driver immediately sends a device removal notification to the bus driver, and then checks for the presence of a card.
This verification step is required in case the card is still present or is exchanged for a different card while the system is suspended. If a card is present, the bus driver is notified. As soon as the previous client driver has been removed, a new client driver is loaded.
In most cases, handling power on and off notifications can be made transparent to the client driver and the client driver can ignore them. When the OS suspends and resumes, the client driver should expect to be unloaded as if a user had ejected the card.