10

ATSAM9708

1772D–DRMSD–01/04

The PDSP#1 responds on addresses 0 to 3 (A2A1A0 = 0XX), while PDSP#2 responds

on addresses 4 to 7 (A2A1A0 = 1XX).

Each PDSP parallel interface supports a byte-wide I/O interface and a 16-bit port dedi-

cated to burst transfers.

The byte-wide I/O interface is normally used to implement a MPU-401 UART-mode

compatible interface. It is specified by address A1A0 = 0X, address 00 being the data

register, address 01 being the status/control registers. Besides the standard two status

bits of the MPU-401, two additional bits are provided to expand the MPU-401 protocol.

Address A1A0 = 10 specifies a 16-bit I/O port. It is mainly used for burst audio transfers

to/from the PC using very efficient PC instructions like REP OUTSW or REP INSW

which operate at maximum ISA bus bandwidth. This port may also be used for fast pro-

gram or sound bank uploads.

DSP Cache RAM

The memory management unit (MMU) allows external ROM and/or RAM memory

resources to be shared between the two DSPs and the two P16 control processors. This

allows a single device (i.e., DRAM) to serve as sample memory storage/delay lines for

the DSPs and as program storage/data memory for the P16 control processors.

The DSP cache RAM allows a dramatic reduction in the traffic with the external

ROM/RAM, allowing use of standard 90 ns ROM parts with sampling frequencies up to

48 kHz. Average access request rate to external memory is only one for every two

frames for each slot, which gives 64 accesses per synthesis frame. The MMU can pro-

vide up to 169 memory accesses per frame, which leaves over 100 accesses free per

frame to be used by the P16 processors. This means that under full 128-voice polyph-

ony traffic conditions, each P16 instruction average execution time is around 400 ns at

48 kHz sampling frequency.

128-voice polyphony can be assured only when all samples are played at nominal fre-

quency or down-transposed. Simultaneously playing a large number of up-transposed

samples can adversely affect polyphony. For more details of possible polyphony for a

given application, please refer to the application note “ATSAM9708 Memory Manage-

ment Unit”.