Atmel SAM9X25, Manual

Page: 475 / 1145

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an interrupt to signal the completion of the DMAC transfer. You can then re-program the channel
for a new DMAC transfer.
Single-buffer DMAC transfer: Consists of a single buffer.
Multi-buffer DMAC transfer: A DMAC transfer may consist of multiple DMAC buffers. Multi-buf-
fer DMAC transfers are supported through buffer chaining (linked list pointers), auto-reloading of
channel registers, and contiguous buffers. The source and destination can independently select
which method to use.
– Linked lists (buffer chaining) – A descriptor pointer (DSCR) points to the location
in system memory where the next linked list item (LLI) exists. The LLI is a set of
registers that describe the next buffer (buffer descriptor) and a descriptor pointer
register. The DMAC fetches the LLI at the beginning of every buffer when buffer
chaining is enabled.
– Replay – The DMAC automatically reloads the channel registers at the end of each
buffers to the value when the channel was first enabled.
– Contiguous buffers – Where the address of the next buffer is selected to be a
continuation from the end of the previous buffer.
Picture-in-Picture Mode: DMAC contains a picture-in-picture mode support. When this mode is
enabled, addresses are automatically incremented by a programmable value when the DMAC
channel transfer count reaches a user defined boundary.
Figure 31-4 on page 475 illustrates a memory mapped image 4:2:2 encoded located at
i m a g e _ b a s e _ a d d r e s s i n m e m o r y . A u s e r d e f i n e d s t a r t a d d r e s s i s d e f i n e d a t
Picture_start_address. The incremented value is set to memory_hole_size = image_width -
picture_width, and the boundary is set to picture_width.
Figure 31-4. Picture-In-Picture Mode Support
Channel locking: Software can program a channel to keep the AHB master interface by locking
the arbitration for the master bus interface for the duration of a DMAC transfer, buffer, or chunk.