PDSP16515GCPR datasheet(7/27 Pages) MITEL

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PDSP16515A

The internal workspace is double buffered when 256 point

transforms are to be performed. A separate output buffer is

also provided. These resources, together with separate input

and output buses, allow new data to be loaded and old results

to be dumped, whilst the present transform is being computed.

Additional, external, input buffering is not needed to prevent

loss of incoming data whilst a transform is being performed.

When block overlapping is required, internally stored data will

be re-used, and a proportionally smaller number of new

samples need be loaded.

Note that the internal window

operator still functions correctly since it is actually applied

during the first pass, and not whilst data is being loaded. The

internal RAM organisation is shown in Fig. 4. It should be

noted that the amount of overlap between I/O transfers and

transforms is completely under the control of the system, since

an input enable signal (INEN) and an output enable (DEN) can

be used to initiate transfers.

In the 1024 point mode there is insufficient workspace for input

and output buffering in addition to working memory. The

device is then configured in a mode with separate load,

transform and dump operations. The internal arrangement is

shown in Fig. 5. The support of an external input buffer is

needed if incoming samples are not to be lost whilst a

Table 1. Advanced Timing Information with Continuous Inputs.

TSD

THD

TSA

THA

N/2

TSI

THI

VALID

TFH

TFL

TFH

50% Overlap

TFL

TSA

TED

DIS

DATA IN

INEN

LFLG

INEN

Edge activated

system

Min Time =THA

transform is in progress. This is loaded at the sample clock

rate and transferred to the FFT processor as quickly as

possible. In this mode the PDSP16515A always expects to

receive 1024 words, regardless of the amount of block

overlapping. Data stored internally cannot be re-used when

block overlapping is required, and data from the external

buffer must be re-read as necessary.

If no incoming data is to remain un-processed, the user must

ensure that the time taken to acquire sufficient data to instigate

a new transform is greater than or equal to the transformation

time itself. The latter can be calculated from Table 4, once the

system clock rate has been defined. When 1024 point

transforms are performed, both the time to read data from the

input buffer, and also the time to dump data, must be included

in the calculation to determine the minimum time in which data

can be loaded into the external buffer.

The peak transfer rate is limited by the characteristics of the I/

O circuits, but can be greater than the sampling rate which is

determined by the transform time. When load and dump

operations are not concurrent with transform operations ( as

in the 1024 point modes ), then the maximum I/O rate is equal

to the system clock rate, Ø. When other transform sizes are

specified, the sampling rate, S, is reduced by a factor F. This

Characteristic

Symbol

Min

Max

Units

Data In set up Time

Data In Hold Time

0ns

INEN active going set up

8ns

INEN active Hold Time

0ns

INEN in-active Hold Time to ensure no load

2ns

INEN in-active going set up for no load operation

8ns

Delay to LFLG going active ( 30 pf load )

Delay to LFLG going in-active ( 30 pf load )

Min time to INEN low in edge mode

PDSP16515GCPR Datasheet(PDF) 7 Page - Mitel Networks Corporation

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