Service_SDIOSlotReleased (changes)

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SDIODriver

» Service Calls

» Service_SDIOSlotReleased

Service_SDIOSlotReleased

(Service &81045)

Use

This service is used to notify the OS that a slot has been released.

Notes

This service call is issued just before exclusive access to an SDIO slot is released. It is particularly useful in reducing the overhead of frequently issued SD commands, because it enables software to determine whether anyone else might have changed the card state (deselected the card, set a different block size and so on). In the common case where this doesn’t happen, it means a number of SD commands can be omitted, allowing increased throughput.

To guard against reentrancy, the procedure that should be employed is thus:

1. Allocate two flags, flag A to say that nobody else claimed the slot since you last did, and flag B to say that you have currently claimed the slot
2. Call SDIO_Control to claim the slot
3. SDIO_Control returns (if this fails then stop here)
4. Set B
5. Issue SD commands – fewer will be needed if A is set
6. Set A
7. Call SDIO_Control to release the slot
8. Service_SDIOSlotReleased handler is entered with B set on entry; clear B
9. At this point, interrupts may happen and further instances of Service_SDIOSlotReleased may occur with B now clear on entry; clear A if so
10. SDIO_Control (from step 7) returns
11. More instances of Service_SDIOSlotReleased may still occur with B clear on entry; clear A if so

This service call may have an additional benefit to enable a background process to be woken up if it previously found that the slot was not available. However you should note that the slot cannot be acquired from within the service call handler. Instead, you should schedule the background process to execute at a later time, for example using OS_CallAfter, OS_AddCallBack or the RTSupport module.

See also

• OS_AddCallBack
• OS_CallAfter
• RTSupport
• SDIO_Control
• Service_SDIOSlotAcquired