The heterogenous design of Field Programmable Gate Arrays (FPGAs) often requires the optimization of the devices to work speedily. When that doesn’t happen, the devices begin to lag and eventually perform below expectations.
Carry4 Xilinx has been designed to help resolve some of these challenges. In this article, you will learn more about it.
What is Carry4 Xilinx?
It is a carry chain that helps facilitate the speed of FPGAs. The Carry4 Xilinx is a dedicated feature in the Xilinx 7 series FPGAs optimized to bolster the arithmetic operations of these FPGAs.
By arithmetic operations, we mean both the adders and counters. In terms of the counters, the construction or development is done via the use of T flip-flops. These are dedicated flip-flops that aid in the toggling of the clock functions for maximum performance.
Xilinx’s Carry4 Architecture
The architecture of the Carry4 Xilinx involves the use of a fast carry logic per slice. On its part, the carry chain is optimized with a series of XORs and MUXes, with each being four (4) in number.
Both the MUXes and XORs are connected to the other logics, an example being the Lookup Tables (LUTs). Through the connection, the fast carry chain logic connects the logics to the slice for the formation of complex functions through the dedicated routes.
Benefits of the Carry4 Xilinx
Here are some of the reasons why you want to use the dedicated logics in the Carry4 Xilinx for your next FPGA project.
1. Clocking Regulation
The performance of the dedicated clocks is improved via the toggle feature of the Carry4 Xilinx. By toggling to the Q output, the Carry4 Xilinx helps to regulate the clocking performance when its T flip-flop input is high. On the other hand, it can stop the output from toggling if the T flip-flip’s input is low.
2. Development of Arithmetic Functions
Carry4 Xilinx also plays an important role in the development of useful arithmetic functions, especially for the core blocks like:
- Subtracters
- Adders
- Address decoders
- Counters
- Specific logic gates, including AND and OR.
- Add/subs
- Wide comparators
Optimizing the Carry4 Xilinx for Speed
Making sure that the FPGA runs smoothly is one of the core functions of the Carry4 Xilinx. However, some constraints can come in at one point or the other. A clear example are the lapses encountered when using the local routing pathway as the carry chain for the device. It typically happens when the FPGA software maps the bits next to each other when required to implement a binary counter.
There is a way out, though. By heavily optimizing the FPGA’s logic elements, the devices may be able to run faster. The speed is also bolstered by positioning the logic elements to run along the carry chain path.
Extra Routing Signal
New FPGAs are optimized for speed by enabling side-by-side placement of the logic elements. It is better and speedy than the general-purpose routing structures that are sometimes slow.
This time, the side placement of these logic elements leads to the provision of an extra local routing signal. Although it can be slow at times, the signal aligns with the software to speed up the bit stream mapping.
Final Thoughts
Carry chains or the Carry4 Xilinx help to cut down the logic gates in an FPGA, as they grow in size. By breaking down the size of these gates, the chains are now able to process the signals faster.
