The minimum number of bits required for the adders in a CIC filter depends
on the decimation rate. Higher decimation factors require more bits. This
means for a multirate filter the size of the logic structures is determined
by the highest supported rate.
The current implementation of the filter always uses all bits of the
structure to compute the results, that means even when running with the
lowest decimation factor all the bits that are required for the highest
decimation factor are used. This will work fine as additional bits do not
affect the output of the filter.
This patch implements dynamic partial gating of the filter structure based
on the selected decimation factor. Bits that are not required for a certain
rates are gated and the carry bits are masked from propagating through the
adder chain. This results in significant power savings at smaller
decimation factors.
This means that the filter itself is now using more power the higher the
decimation rate. But this is offset by the reduced data output rate running
subsequent processing stages at a lower rate and reducing power consumption
there. This results in a more or less flat power profile regardless of
decimation factor.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
The minimum decimation of the CIC block is 5. This means new data arrives
at the comb stages at most every 5 clock cycles. Rather than letting the
logic sit idle during those 4 extra cycles use it to sequentially process
the comb stages of the filter. This reduces the logic utilization of the
filter by quite a bit.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Re-implement the CIC using the basic building blocks from the util_cic
library.
This new implementation is structurally equivalent to the previous version,
but will be used as a platform for implementing changes that will improve
area and power consumtion of the filter
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Lars-Peter Clausen
Adrian Costina