Sd I/O Suspend And Resume; Sd I/O Readwait - Motorola DragonBall MC9328MX1 Reference Manual

The interrupt period is applicable for both memory and I/O operations. The
definition of the interrupt period for operations with single blocks is
different from the definition for multiple block data transfers.

20.7.7.2 SD I/O Suspend and Resume

Within a multi-function SD I/O or a card with both I/O and memory functions, there are multiple devices
(I/O and memory) that share access to the MMC/SD bus. To share access to the MMC/SD module among
multiple devices, SD I/O and combo cards optionally implement the concept of suspend/resume. When a
card supports suspend/resume, the MMC/SD module can temporarily halt a data transfer operation to one
function or memory (suspend) to free the bus for a higher priority transfer to a different function or
memory. After this higher-priority transfer is complete, the original transfer is resumed (re-started) where
it left off. Support of suspend/resume is optional on a per-card basis.
To perform the suspend/resume operation on the MMC/SD bus, the MMC/SD module performs the
following steps:
1. Determines the function currently using the SD_DAT [3:0] line(s).
2. Requests the lower priority or slower transaction to suspend.
3. Waits for the transaction suspension to complete.
4. Begins the higher priority transaction.
5. Waits for the completion of the higher priority transaction.
6. Restores the suspended transaction.

20.7.7.3 SD I/O ReadWait

The optional ReadWait (RW) operation is defined only for the SD 1-bit and 4-bit modes. The ReadWait
operation allows the MMC/SD module to signal a card that it is reading multiple registers
( , CMD53) to temporarily stall the data transfer while allowing the MMC/SD module to
IO_RW_EXTENDED
send commands to any function within the SD I/O device. To determine when a card supports the
ReadWait protocol, the MMC/SD module must test capability bits in the card internal registers. The timing
for ReadWait is based on the interrupt period. Code Example 20-13 on page 20-54 provides the
programming code for the SD I/O RW operation.
MOTOROLA Multimedia Card/Secure Digital Host Controller Module (MMC/SD)
Functional Example for the MMC/SD Module
NOTE:
20-53