FPGA and PLC

“But who’s going to pay my salary?”

In retrospect it would have been better to go ahead and change the precedence of & to

higher than ==, but it seemed safer just to split & and && without moving & past an existing operator. (After all, we had several hundred kilobytes of source code, and maybe 3

installations....)

the order in which these groupings will be evaluated is always undefined. In the expression:

x = f() + g() * h();

The values returned by g() and h() will be grouped together for multiplication, but g and h

might be called in any order. Similarly, f might be called before or after the multiplication,

or even between g and h. All we can know for sure is that the multiplication will occur

before the addition (because the result of the multiplication is one of the operands in the

addition). It would still be poor style to write a program that relied on that knowledge. Most

programming languages don't specify the order of operand evaluation. It is left undefined so

that compiler-writers can take advantage of any quirks in the architecture, or special

Avoid unnecessary complexity by minimizing your use of unsigned types. Specifically,

don't use an unsigned type to represent a quantity just because it will never be negative

(e.g., "age" or "national_debt").

Use a signed type like int and you won't have to worry about boundary cases in the

detailed rules for promoting mixed types.

Only use unsigned types for bitfields or binary masks. Use casts in expressions, to make all

Most Xilinx IP come with constraint fi les (.xdc). They can contain physical constraints such as setting IO standards or locations and timing constraints, such as false paths. These two types can be mixed in the same fi le. The constraints are written as if the IP were the top of the design. The constraints are automatically scoped to IP instance(s). It is strongly recommended that you do not modify the constraints delivered by an IP. There are two sources of constraints used by IP. If you’re a user of IP from the available catalog, you need not worry about this distinction. However, this distinc- tion would be of importance, if you are creating an IP of your own:

• XDC fi les created during generation of the IP and contained in the IP directory

or the Core Container

• Managed IP Project (recommended)

• Directly from within a Vivado RTL project

• Using Tcl script

Managed IP Project

It is recommended when working with IP that you use a Managed IP project. This is a special Vivado project specifi cally for creating IP customizations. The same IP

Catalog found in a Vivado RTL Project is provided to search for and customize IP. Each IP created is kept in its own folder with the user-provided name used during the customization. If you elect to use the Core Container feature (explained in Sect. 3.4.3 ), a single compressed binary fi le with the name given during customization with the extension of .xcix will be present. The IP folder or Core Container fi le

IPI also provides a feature wherein you can package the entire block design after it has been validated and functionality has been proven. This allows you to reuse the IP block design in other projects as well. Figure 7.3 depicts the selection window for

With the complexity of the systems increasing exponentially, it becomes extremely important to be able to reuse designs with minor modifi cations to their systems without

Any methodology for creating an optimal RTL implementation ideally requires understanding what the requirements of the RTL implementation are. However, the following methodology assumes you wish to create the highest-performing design.

If this is not the case, skip steps 4 and 5:

1. Simulate the C design and ensure the results are checked in the testbench.

2. Synthesize the C code to create a baseline design. This will be the default syn-

thesis performed by HLS and provide you with a starting point for optimization.

3. Apply the optimizations for interface synthesis. This ensures the interfaces are of

the required type to integrate the design with the rest of the system.

4. Apply pipeline directives.

5. Address any structural issues which create bottlenecks and prevent pipelining

achieving the desired II , such as partitioning arrays and unrolling loops.

6. Use the optimization directives which control the allocation of resources to

improve the area if this is required.