External Port Dma - Analog Devices ADSP-2106x SHARC User Manual

6 DMA
restart at the new count.
6.4

EXTERNAL PORT DMA

Channels 6, 7, 8, and 9 are the external port DMA channels, which are
available on the ADSP-21060 and ADSP-21062. On the ADSP-21061,
only channels 6-7 are available. These DMA channels allow efficient
data transfers between the ADSP-2106x's internal memory and external
memory or devices.
6.4.1 External Port FIFO Buffers (EPBx)
DMA Channels 6, 7, 8, and 9 are associated with the external port FIFO
data buffers, EPB0, EPB1, EPB2, and EPB3. Each buffer acts as a six-
location FIFO. It has two ports, a read port and a write port. Each port
can be connected to either the EPD (External Port Data) bus or to a local
bus which in turn can connect to the IOD (I/O Data) bus,
bus, or DM Data bus. (See Figure 6.2.) This structure allows data to be
written to the FIFO on one port while it is being read from the other
port—allowing DMA transfers at the full processor clock frequency.
The external port FIFO buffers can also be used for non-DMA, single-
word data transfers, as described in the Host Interface chapter of this
manual.
Caution: The ADSP-2106x core should not attempt to read or write an
EPBx buffer when a DMA operation using that buffer is in progress;
this will corrupt the DMA data.
Each external port buffer can be flushed (i.e. cleared) by writing a 1 to the
FLSH bit in the corresponding DMACx control register. This should only be
done when DMA is disabled for the channel. The FLSH bit is not latched
internally and will always be read as a 0. Status can change in the following
cycle. An external port buffer should not be enabled and flushed in the
same cycle.
6.4.1.1 External Port DMA Data Packing
Each external port buffer contains data packing logic to allow 16-bit or
32-bit external bus words to be packed into 32-bit or 48-bit internal
words. The packing logic is also fully reversible, depending on the
setting of the TRAN bit in the DMACx control register, so that 32-bit or
48-bit internal data can be unpacked into 16-bit or 32-bit external word
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