AR# 3846


COREGEN: Tips on simulating the SDA FIR filter


General Description:
There are a number of things to note when simulating the
SDA FIR Filter core produced by the CORE Generator.


The SDA FIR Filter is available in v1.4.1 and later versions of the CORE

1. The latest version of this core (v1.14 or later) can be
found on the Xilinx CORELINX web site,

To simulate the filter:

2. You should assert global reset for at least one clock
cycle to initialize the entire design. This is a gneral rule
for any design that contains flip-flops and/or latches.

3. When RFD goes high, you can then assert the first data.
The input data and the ND input must both be stable for some
period of time before the data is clocked in on the next
rising clock edge. Asserting both ND and data shortly after
the falling edge of the clock should ensure that this
requirement is met. ND ("New Data") can be asserted (driven
high) on the same falling clock edge as the data, and should
be asserted for one clock cycle.

4. The state of ND should always be defined, and ND should
NEVER be asserted when RFD is low. If this ever occurs, the
filter's operation will become undefined for a number of clock
cycles. During this period, the behavioral model and the
actual filter behavior will not match.

5. The output on the RSLT port will be valid when RDY goes
high. You must ignore the output at RSLT at all other times.

6. Due to an issue (CR 103333) with the way full precision
output width is calculated, the TRIM EMPTY ROMS options
will usually give you a result which is inconsistent with
what you may expect.

To avoid this problem, you should allow always direct COREGEN
to generate the core with the full precision output bus width.
The full precision output width value is noted under the
Output Width field in the FIR filter GUI for the specific
data and coefficient widths that you specify. However,
the field is not pre-set as the default value, so you must
manually enter that value in the field. Then simply leave unconnected
those output bits that you do not need.

In other words, do not select anything smaller than the full
precision value displayed in the GUI for the FIR filter output
AR# 3846
Date 05/14/2014
Status Archive
Type General Article
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