External Address Calculation For Reads - Analog Devices SHARC ADSP-214 Series Hardware Reference Manual

External Port DMA
single reads from each TAP are shown for simplicity and block reads are
default, depending on the count specified in the
1. Writes to external memory. The number of writes is determined by
the
ICEP
register is used as the internal modifier. The
IMEP
serves as the external index and is incremented by the
after each write. These writes are circular buffered if circular buff-
ering is enabled.
2. In chained DMA, when the writes are complete, (
register, which serves as the write pointer of the delay line, is
EIEP
written back to the internal memory location from where it was
fetched.
3. Reads from external memories. For reads, the tap list (TL) modifi-
ers are used and the number of reads is determined by the
register. The write pointer in the
address for these reads (reads start from where writes end). The
register, along with tap list modifiers, are used in a pre-modify
EIEP
addressing mode to create the external address for the writes.
Therefore, for each read, the DMA controller fetches the external
modifier from the tap list and the reads are circular buffered (if
enabled).

External Address Calculation for Reads

Note that TL[N] is the first tap list entry in internal memory pointed to
by the tap list pointer register (
integers. Therefore, for each read-block, the DMA state machine fetches
the offset external modifier from the tap list. The reads are circular buff-
ered if circular buffering is enabled.

The external address generation follows pre-modify addressing for
reads in delay line DMA and therefore the
not modified. Also the
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register. The data is fetched from the
TPEP
EMEP
ADSP-214xx SHARC Processor Hardware Reference
RCEP
IIEP
register serves as the index
EIEP
). Tap list entries are 27-bit signed
EIEP
register does not have any effect during
register.
register and the
register
EIEP
register
EMEP
= zero) the
ICEP
RCEP
register values are