Motorola DSP56009 User Manual page 131

The EMI architecture is capable of managing several concurrent data-delay
processes. Each data-delay buffer is defined by its own base address. Multiple
data-delay buffers can be implemented by saving and restoring the contents of the
EBARx as required. The maximum delay required in a data sequence implicitly
determines the data-delay buffer length. Two restrictions must be considered:
• The programmer must define non-overlapping initial memory regions for the
data-delay buffers within the available memory address range.
• The data-delay buffers must be updated at the same speed; that is, new data
samples are stored at the same rate in all buffers. This ensures that no
data-delay buffer will overwrite the data of another buffer.
Normally, the DSP programmer determines the base address values arbitrarily such
that non-overlapped buffers are guaranteed. This is done in the initialization stage
only. Afterwards, the programmer need not be concerned with the base address
value.
To summarize, the data-delay buffer is normally handled, in the steady state (after
initialization and buffer-filling stage), as follows:
• Upon receiving a new data sample, the data sample is temporarily saved in an
internal memory location. It might be used in many audio algorithms as the
most recent data sample.
• Any number of random-delayed samples are read from the specific buffer in
the external memory by requesting read operations with different offset
values while EBARx is loaded with the base address for the specific data
buffer. This is operation is accomplished by writing the desired offset values
to the EOR, triggering the read operation. The contents of EBARx should be
kept constant during the read operations; that is, keep EINR = 0 in the ECSR.
• The most recent data sample (temporarily held in an internal memory
location) is stored to the specified data buffer in the external memory by
writing the data word to the Data Write Register when EINW (in the ECSR) is
set. In this way the new sample is stored in the external memory data buffer
while EBARx is incremented, preparing the base address for the next sample.
• The contents of EBARx should now be saved to an internal memory location
to be used in future accesses to this data-delay buffer.
MOTOROLA DSP56009 User's Manual
External Memory Interface
Data-delay Structure
4-47