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Using the Carry-Save Adder, Computing a Running Average  I will show in the next few posts some design examples where using a 3-input carry-save adder instead of the normal 2-input ripple-carry adder makes a significant difference. The first example is a running average, where we have a stream of input samples and we want to compute a continuous running average every clock, as the average of the last N samples. In mathematical terms:   y(n)=1/N*Sum(x(n-k)), k=0..N-1   As a firs ...
This is  a little test board I'm putting together to experiment with the MAX32660 processor and the Lattice UP5K Ultra Plus FPGA.   The UP5K is a tiny FPGA, available in a hand solderable 48 pin, 0.5mm pitch QFN with 5k LUTs, 15k bytes of embedded block RAM and 128k bytes of SPRAM (slowish ram in 32k byte blocks). It has 8 multipliers (16 x 16) and draws a static current of 75uA. They cost pocket money, about £5 a few at a time.   It's a volatile FPGA so it needs something ...
The Carry-Save Adder, two for the price of one  This post is about buying two adders but paying only for one of them.   When developing software the CPU and memory your code is running on is already paid for and there is little incentive to optimize your code to make it either smaller or faster. But as a hardware designer you literally pay for every LUT and FF in the FPGA you are using. If you could make your design smaller and faster you could do more with the same FPGA or you could ...
This is an update of my on going N64 HDMI conversion project. The N64=>HDMI Conversion Project As of right now I have identified that the RCP (or the GPU) have common outputs between board revisions for the video and audio. There is a seven bit word, Dsync, and clock that contribute to the digital video signal. These are connected to a DAC that outputs an RGB signal. The plan is to rob these signals on there way to the DAC in order to reduce complexity and latency of the FPGA design. I have ...
Counters, Adders and Accumulators  One of the most common operation encountered in digital hardware design, especially for digital signal processing applications, is addition. This actually covers a large group of fundamental building blocks, like up/down binary counters, adders/subtractors, comparators, accumulators and so on. The signal types operated on can be IEEE.numeric_std SIGNED/UNSIGNED for integer operands, the user defined SFIXED introduced earlier, or the default VHDL-2008 type ...
This is a continuation of this post: Custom Vivado Parts/Board Creation and this post:Nintendo 64 Schematic   I plan on adding to this blog and over time creating a documented progression of the project.   For those who did not take the time to go through that post (though you definitely should find the time), here are the cliff notes. I am a computer engineering student. My end project is to convert raw N64 GPU data (and audio) to HDMI. It will require I design my own board a ...
The Universal MUX Building Block Part 3, the one with the Dutch Cocoa Box and the Ouroboros  We have seen in the previous post that Vivado Synthesis is able to optimally infer a mux form behavioral code for multiplexers with up to 16 inputs, but beyond that not so much. The synthesis results are not bad but for high performance designs where every LUT and especially every logic level counts not bad is not good enough.   So in this post I will present a solution to this problem, that ...
The Universal MUX Building Block Part 2  So the question is now what is the most efficient implementation for arbitrary size multiplexers one should expect? If the result the synthesis tools infers from behavioral code is equal or very close to this there is no need for a specialized MUX Building Block. If the difference is significant then there will be a definite need for such a block, especially for designs with large muxes and/or many of them.   To simplify the analysis we will f ...

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