Hello.
I now have 53bit corgen adder in my design. In order to upgrade the speed, I will do something about 53 bit adder. so Is there anyone who know which one between Corgen and DSP48 is faster?
ps If there is none..... I will test them.
Especially at your bit-width, the LUT based adder will be much faster.
---Matthew Hicks
The DSP48 is considerably faster for 53 bits, assuming you are pipelining your add. You will have to cascade two of them to get that width, which means using the lower one as a 35 bit adder to get bit 36 out as a carry out, and adding appropriate delays to the input of the upper and output of the lower sections.
Unless you can afford 3 cycles of latency, a DSP based adder will be the slowest option. I have tested a group of 36-bit two input adders that were implemented in HDL via the + operator, using Xilinx LUT based IP, and using Xilinx DSP48 based IP on a Virtex-4. The HDL operator based adder was the fastest for combinational adds (it was only 1MHz faster than the LUT based IP adder with the same resource usage). The added advantage of the HDL adder is that it is portable across FPGAs and much easier to work with.
---Matthew Hicks
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