PDSP16510A Datasheet, PDF (20/23 Pages) Mitel Networks Corporation – Stand Alone FFT Processor

PDSP16510A
(4) OUTPUT SCENARIOS
Considering the above sequence, therefore, some single
device situations can now be explained :
(4.1) DOS is continuously present, but DEN is inactive
(Transform size less than 1024)
In this case, when the transform is complete, as the
device is programmed as a single device and DEN is
inactive, DAV will be made active. Even though DOS
is running, the status of DAV at this point does not rely
on it.
The user can now monitor the status of DAV, and after
at least 6 SCLK cycles can initiate some further action,
eg by external control force DEN active at some later
time when the rest of the system is ready to accept the
transformed data. Independently of this external
control, the next DOS pulse will start to operate the
sequence of events as described above (ie point No.
3.3). When DEN is eventually made active, the
remainder of the above sequence (points Nos 3.4 to
3.7) is executed, with 4 DEN-Enabled DOS pulses
needed before data is observed on the output pins.
If however the user immediately forces DEN active
upon monitoring DAV go active and waiting for the
required 6 SCLK cycles, then 5 DOS pulses would
have to be issued. The first of these 5 would start the
sequence of events as described above (3.3), and the
fact that it is enabled by DEN would be irrelevant. The
required DEN enabled pulses in this situation would be
the 2nd, 3rd, 4th and 5th pulses supplied.
(4.2) DOS is not running, and DEN is inactive. (Transform
sizes less than 1024)
In this situation, again as the device is programmed to
be a single device and DEN is inactive at the point
where the transform is complete, DAV will be made
active regardless of the state of DOS. The user can
now monitor this event on DAV and after waiting a
further 6 SCLK cycles, use it to switch on DOS and to
make DEN active.
DOS can now be switched on for at least one pulse (but
may be more), and the sequence of events as
described earlier (from point No 3.3) will start. DEN can
then be made active, whereby a further 4 DEN-
Enabled DOS pulses will be required before data is
seen on the output pins. This is the situation shown in
table 3.
Alternatively, DEN and DOS could be made to operate
on the same cycle. In this case data will appear on the
output pins on the 5th DOS pulse (the first would not
actually require the presence of DEN, but the 2nd, 3rd,
4th and 5th would)
(4.3) 1024 point transforms, single device mode.
In the case of 1024 point transforms, the internal RAM
is no longer operated in the manner described in
section 2. The RAM is instead totally dedicated to one
operation at a time. Thus data for a transform will be
loaded, and all 12 out of 12 SCLK cycles will be
available for the transfer of input data to the RAMs.
During the transfrom no transfers from the input to the
RAM or from the RAM to the output are possible. This
is why DIS and DOS can be equal to SCLK for 1024
point transforms.
If 1024 point transforms are being performed and the
device is programmed as a single device, then
"asynchronous" operation of DAV is possible as
described earlier for transform sizes less than 1024
points. If DEN is inactive at the time the transform has
finished calculating, then DAV will be made to go active
regardless of the state of DOS. Although 6 SCLK
cycles do not have to be waited for as in section 3.2, a
transition has to be made from the transform
controlling the internal RAM to the output circuits
cnotrolling it. This operation plus the time taken to
advance data from the RAMs to the output buffer takes
exactly 4 SCLK cycles.
Hence the sequence of events is exactly as described
in section 3, except that section 3.3 should read 4
SCLK cycles rather than 6. The analysis of sections 4.1
and 4.2 are also true if the 6 SCLK cycle time is
substituted with 4 SCLK cycles.
(5) DUMMY DOS STROBES AFTER DEF
In addition to the dummy DOS strobes needed prior to
dumping data, it is necessary to provide at least 4 DOS strobes
after DEF has gone inactive, but before DAV goes active.
These initialise the internal address counters and do not rely
on DEN also being active. They are needed every time DEF
has been used to change the operating mode.
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