Data Alignment; Synchronizing Channel Activity - Texas Instruments OMAP5912 Reference Manual

Multimedia processor device overview and architecture

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Data Alignment

During a transfer, all the addresses computed by the DMA must be aligned on

the type of data transferred:

If the data type is s8 (8 bits scalar data), addresses can have any value.

If the data type is s16 (16 bits scalar data), addresses must be aligned on

16-bit word boundary (the least bit of the address is always 0).

If the data type is s32 (32 bits scalar data), addresses must be aligned on

32-bit word boundary (the two least bits of the address are always 00).

Activity in a channel can be synchronized to an event in a DSP peripheral or

to an event signaled by the driving of an external interrupt pin. Use the

synchronization bits of DMA_CCR to specify which synchronization event (if

any) triggers activity.

Each channel also has an FS bit in DMA_CCR that enables choosing between

two synchronization modes:

Element synchronization mode (FS = 0) requires one event per element

transfer. When the selected synchronization event occurs, a read access

request is sent to the source port, and then a write access request is sent

to the destination port. When all the bytes of the current element are

transferred, the channel makes no more requests until the next

occurrence of the synchronization event.

Frame synchronization mode (FS = 1) requires one event to trigger an

entire frame of elements. When the event occurs, the channel sends a

read access request and a write access request for each element in the

frame. When all the elements are transferred, the channel makes no more

requests until the next occurrence of the event. If a synchronization event

is specified, the source port does not receive an access request until the

event occurs. Once the request is received, it is handled according to the

predefined position and the programmed priority of the channel in the

DMA service chain (see Section 4.4, Service Chain). To avoid long delays,

it is best to give all synchronized channels a high priority. If the choice is

made not to synchronize the channel (synchronization = 00000b), the

channel sends an access request to the source port as soon as the

channel is enabled (EN = 1 in DMA_CCR).

Direct Memory Access (DMA) Support

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