With the increasing complexity of VLSI, the time and economic cost of testing after circuit manufacturing are also increasing. In the past, people focused most of their energy on the design itself without considering the subsequent tests, because the tests were relatively simpler at that time. In recent years, testing itself has gradually become a huge topic. For example, it is easy to control some internal signals from the outside of the circuit so that they present specific logic values, while some internal signals are difficult to change their values directly from the outside because they depend on a large number of other internal signals.

Integrated circuit design

In addition, the change of internal signal can not be observed at the main output terminal many times (sometimes the signal output of the main output terminal seems to be correct, but the internal state is wrong. Only observing the output of the main output terminal is not enough to judge whether the circuit works normally). The above two kinds of problems, namely controllability and observability, are the two components of testability. It is gradually found that adding some special structures (such as scan chain and built-in self-test) to the circuit design can greatly facilitate the subsequent circuit test. Such designs are called testability design. They make the circuit more complex, but they can reduce the cost of the whole project with simpler testing. With the increasing integration of VLSI and the increasing pressure of market competition, reusable design methodology is gradually introduced into IC design. The main significance of reusable design methodology is that suppliers providing IP core (intellectual property core) can provide some pre completed designs to designers in the form of commodities, which can use IP core as a complete module in their own design projects. Thus, when implementing similar functions, companies do not need to repeatedly design similar modules. Although this will increase the commercial cost, it will also significantly reduce the complexity of the design, so as to shorten the cycle required by the company to design large circuits, so as to improve the market competitiveness. The products provided by IP core suppliers may be verified hardware description language codes. In order to protect the supplier's intellectual property rights, these codes are often encrypted. IP core itself is also designed as an integrated circuit, but in order to be applied in different design projects, it will focus on strengthening its portability, so its design code specification is more strict. Some chip companies specialize in the development and sales of IP cores. Arm is a typical example. These companies make profits through the authorization of intellectual property rights.