The most important part of the men's golf season is traditionally held in the spring when post-season competition can lead to a national championship.  Before the team entered the spring, Head Golf Coach Gary Tanner recognized four players for their past performance at a recent home volleyball match.

1 Dominican Peso = 0.1285 Chinese Yuan Renminbi

1 Dominican Peso = 15.0036 Chilean Peso

1 Papua New Guinean Kina = 2.0622 Chinese Yuan Renminbi

1 Papua New Guinean Kina = 240.7325 Chilean Peso

1 Brunei Dollar = 5.0056 Chinese Yuan Renminbi

1 Brunei Dollar = 584.3256 Chilean Peso

Test chips are becoming more widespread and more complex at advanced process nodes as design teams utilize early silicon to diagnose problems prior to production. But this approach also is spurring questions about whether this approach is viable at 7nm and 5nm, due to the rising cost of prototyping advanced technology, such as mask tooling and wafer costs.

Semiconductor designers have long been making test chips to validate test structures, memory bit cells, larger memory blocks, and precision analog circuits like current mirrors, PLLs, temperature sensors, and high-speed I/Os. This has been done at 90nm, 65nm, 40nm, 32nm, 28nm, etc., so having test chips at 16nm, 7nm, or finer geometries should not be a surprise. Still, as costs rise, there is debate about whether those chips are over-used given advancements in tooling, or whether they should be utilized even more, with more advanced diagnostics built into them.

Modern EDA tools are very good. You can simulate and validate almost anything with certain degree of accuracy and correctness. The key to having good and accurate tools and accurate results (for simulation) is the quality of the foundry data provided. The key to having good designs (layouts) is that the DRC deck must be of high quality and accurate and must catch all the things you are not supposed to do in the layout. Most of the challenges in advanced node is in the FEOL where semiconductor physics and lithography play outsize roles. Issues that were not an issue at more mature nodes can manifest themselves as big problems at 7nm or 5nm. Process variation across the wafer and variation across a large die also present problems that were of no consequence in more mature nodes.

The real questions to be asked are as follows:

What is the role of test chips in SoC designs?

1. Do all hard IP require test chips for validation?
2. Are test chips more important at advanced nodes compared to more mature nodes?
3. Is the importance of test chip validation relative to the type of IP protocols?
4. What are the risks if I do not validate in silicon?

In complex SoC designs, there are many high-performance protocols such as LPDDR4/4x PHY, PCIe4 PHY, USB3.0 PHY, 56G/112G SerDes, etc. Each one of these IP are very complex in and by itself. If there is any chance of failure that is not detected prior to SoC (tapeout) integration, the cost of retrofit is huge. This is why the common practice is to validate each one of these complex IP in silicon before committing to use such IP in chip integration. The test chips are used to validate that the IP are properly designed and meet the functional specifications of the protocols. They are also used to validate if sufficient margins are designed into the IP to mitigate variances due to process tolerances. All high-performance hard IP go through this test chip/silicon validation process. Oftentimes, marginality is detected at this stage. In advanced nodes, it is also important to have the test chips built under different process corners. This is intended to simulate process variations in production wafers so as to maximize yields. Advanced protocols such as 112G, GDDR6, HBM2, and PCIe4 are incredibly complex and sensitive to process variations. It is almost impossible to design these circuits and try to guarantee their performance without going through the test chip route.

Besides validating performance of the IP protocols, test silicon is also used to validate robustness of ESD structures, sensitivity to latch up, and performance degradation over wide temperature ranges. All these items are more critical in advanced nodes than more mature modes. Test chips are vehicles to guarantee design integrity in bite-size chunks. It is better to deal with any potential issues in smaller blocks than to try to fix them in the final integrated SoC.

Test chips will continue to play a vital role in helping IP and SoC teams lower the risk of their designs, and assuring optimal quality and performance in the foreseeable future. They are not going away!

To read more, please visit https://semiengineering.com/test-chips-play-larger-role-at-advanced-nodes/

Hello, i have a logic output from a D-flipflop which generates a reset signal with variable pulse width. I want to stretch this LOW pulse width with an extra 100ns added to the original pulse width digitally, is there any way to do that?

I have been working on a an ASA 17.2 project for the last 6 months.

When I go to Project --> Settings, the settings window does not open. 

The tool indicates that a window is open, as I cannot click on anything else in the project. But it does not show the Settings window.

This has been happening only for the last 2 months. Before that it was working fine.

If I send the project to my colleague, the settings window shows up for him.

Hi Team,

Problem Statement:In hierarchical layout, I want to get BBOX of particular layer without actually flattening the layout.

Description:The layer can be at any hierarchical depth i.e both from PCELL or shapes but at top level if they are overlapping then I want the merged BBOX.

Now, I am able to get BBOX of all the shapes present at different hierarchy.But i finding issue in merging BBOX.

Please can help me on the same issue as I require efficient way to merge the BBOX because list containing the BBOX is huge.

Thanks in advance.

Regrads,

Prasanna

As the stakes for winning server segment market share grow ever higher an increasing number of companies are seeking to grasp the latest Holy Grail of multi-chip coherence. The approach promises to better enable applications such as machine learning...(read more)

https://community.cadence.com/cadence_blogs_8/b/breakfast-bytes/posts/cowos-info

I came across cadence old article that discussing about TSMC advance packaging technology such as InFO & CoWoS. However, I couldn’t find information such as what I/O interface standard is required to realize this multi-chip SiP. For example, Intel using their proprietary AIB interface for EMIB solution.

Besides, any idea if inFO also able to supports multi-chip integration for older node process to new node process such as 40-nm to 16-nm?

Hello, I have a problem with a certain type of transistor,my hyrarchy has a lot components an sub components and visually inspecting them is very hard.

is there a way like in other cadence layout viewer tools , to enter the name of the component or a NET somewhere and it will focus on it visualy or give the hyrarchy path to it?

Thanks.

Hello, i have built a matching network of 13dB gain and  NF as shown bellow step by step.(including all the plots and matlab )

its just not working at all,i am doing it exacly by the thoery

taking a point inside the circle-> converting its gamma to Z_source->converting gamma_s into gamma_L with the formulla bellow as shown in the matlab->converting the gamma_L into Z_L-> building the matching network for conjugate of Z_L and Z_c.Its just not working.

where did i got  wrong?

Thanks.

gamma_s=75.8966*exp(deg2rad(280.88)*i);
z_s=gamma2z(gamma_s,50);
s11=0.99875-0.03202*i
s12=721.33*10^(-6)+8.622*10^(-3)*i
s21=-188.37*10^(-3)+30.611*10^(-3)*i
s22=875.51*10^(-3)-100.72*10^(-3)*i
gamma_L=conj((s22+(s12*s21*gamma_s)/(1-s11*gamma_s)))
z_L=gamma2z(gamma_L,50)

Key Findings: Advantest, in mixed-signal SoC design, sees 50X speedup, 25 day test reduced to 12 hours, dramatic test coverage increase.

Trolling through the CDNLive archives, I discovered another gem. At the May 2013 CDNLive in Munich, Thomas Henkel and Henriette Ossoinig of Advantest presented a paper titled “Timing-accurate emulation of a mixed-signal SoC using Palladium XP”. Advantest makes advanced electronics test equipment. Among the semiconductor designs they create for these products is a test processor chip with over 100 million logic transistors, but also with lots of analog functions.They set out to find a way to speed up their full-chip simulations to a point where they could run the system software. To do that, they needed about a 50X speed-up. Well, they did it!

Figure 1: Advantest SoC Test Products

To skip the commentary, read Advantest's paper here. 

Problem Statement

Software is becoming a bigger part of just about every hardware product in every market today, and that includes the semiconductor test market. To achieve high product quality in the shortest amount of time, the hardware and software components need to be verified together as early in the design cycle as possible. However, the throughput of a typical software RTL simulation is not sufficient to run significant amounts of software on a design with hundreds of millions of transistors.  

Executing software on RTL models of the hardware means long runs  (“deep cycles”) that are a great fit for an emulator, but the mixed-signal content posed a new type of challenge for the Advantest team.  Emulators are designed to run digital logic. Analog is really outside of the expected use model. The Advantest team examined the pros and cons of various co-simulation and acceleration flows intended for mixed signal and did not feel that they could possibly get the performance they needed to have practical runtimes with software testbenches. They became determined to find a way to apply their Palladium XP platform to the problem.

Armed with the knowledge of the essential relationship between the analog operations and the logic and software operations, the team was able to craft models of the analog blocks using reduction techniques that accurately depicted the essence of the analog function required for hardware-software verification without the expense of a continuous time simulation engine.

The requirements boiled down to the following:

• Generation of digital signals with highly accurate and flexible timing

• Complete chip needs to run on Palladium XP platform

• Create high-resolution timing (100fs) with reasonable emulation performance, i.e. at least 50X faster than simulation on the fastest workstations

Solution Idea

The solution approach chosen was to simplify the functional model of the analog elements of the design down to generation of digital signal edges with high timing accuracy. The solution employed a fixed-frequency central clock that was used as a reference.Timing-critical analog signals used to produce accurately placed digital outputs were encoded into multi-bit representations that modeled the transition and timing behavior. A cell library was created that took the encoded signals and converted them to desired “regular signals”. 

Automation was added to the process by changing the netlisting to widen the analog signals according to user-specified schematic annotations. All of this was done in a fashion that is compatible with debugging in Cadence’s Simvision tool.  Details on all of these facets to follow.

The Timing Description Unit (TDU) Format

The innovative thinking that enabled the use of Palladium XP was the idea of combining a reference clock and quantized signal encoding to create offsets from the reference. The implementation of these ideas was done in a general manner so that different bit widths could easily be used to control the quantization accuracy.

Figure 2: Quantization method using signal encoding

Timed Cell Modeling

You might be thinking – timing and emulation, together..!?  Yes, and here’s a method to do it….

The engineering work in realizing the TDU idea involved the creation of a library of cells that could be used to compose the functions that convert the encoded signal into the “real signals” (timing-accurate digital output signals). Beyond some basic logic cells (e.g., INV, AND, OR, MUX, DFF, TFF, LATCH), some special cells such as window-latch, phase-detect, vernier-delay-line, and clock-generator were created. The converter functions were all composed from these basic cells. This approach ensured an easy path from design into emulation.

The solution was made parameterizable to handle varying needs for accuracy.  Single bit inputs need to be translated into transitions at offset zero or a high or low coding depending on the previous state.  Single bit outputs deliver the final state of the high-resolution output either at time zero, the next falling, or the next rising edge of the grid clock, selectable by parameter. Output transitions can optionally be filtered to conform to a configurable minimum pulse width.

Timed Cell Structure

There are four critical elements to the design of the conversion function blocks (time cells):

                Input conditioning – convert to zero-offset, optional glitch preservation, and multi-cycle path

                Transition sorting – sort transitions according to timing offset and specified precedence

                Function – for each input transition, create appropriate output transition

                Output filtering – Capability to optionally remove multiple transitions, zero-width, pulses, etc.

Timed Cell Caveat

All of the cells are combinational and deliver a result in the same cycle of an input transition. This holds for storage elements as well. For example a DFF will have a feedback to hold its state. Because feedback creates combinational loops, the loops need a designation to be broken (using a brk input conditioning function in this case – more on this later). This creates an additional requirement for flip-flop clock signals to be restricted to two edges per reference clock cycle.

Note that without minimum width filtering, the number of output transitions of logic gates is the sum of all input transitions (potentially lots of switching activity). Also note that the delay cell has the effect of doubling the number of output transitions per input transition.

Figure 3: Edge doubling will increase switching during execution

SimVision Debug Support

The debug process was set up to revolve around VCD file processing and directed and viewed within the SimVision debug tool. In order to understand what is going on from a functional standpoint, the raw simulation output processes the encoded signals so that they appear as high-precision timing signals in the waveform viewer. The flow is shown in the figure below.

Figure 4: Waveform post-processing flow

The result is the flow is a functional debug view that includes association across representations of the design and testbench, including those high-precision timing signals.

Figure 5: Simvision debug window setup

Overview of the Design Under Verification (DUV)

Verification has to prove that analog design works correctly together with the digital part. The critical elements to verify include:

• Programmable delay lines move data edges with sub-ps resolution

• PLL generates clocks with wide range of programmable frequency

• High-speed data stream at output of analog is correct

These goals can be achieved only if parts of the analog design are represented with fine resolution timing.

Figure 6: Mixed-signal design partitioning for verification

How to Get to a Verilog Model of the Analog Design

There was an existing Verilog cell library with basic building blocks that included:

- Gates, flip-flops, muxes, latches

- Behavioral models of programmable delay elements, PLL, loop filter, phase detector

With a traditional simulation approach, a cell-based netlist of the analog schematic is created. This netlist is integrated with the Verilog description of the digital design and can be simulated with a normal workstation. To use Palladium simulation, the (non-synthesizable) portions of the analog design that require fine resolution timing have to be replaced by digital timing representation. This modeling task is completed by using a combination of the existing Verilog cell library and the newly developed timed cells.

Loop Breaking

One of the chief characteristics of the timed cells is that they contain only combinational cells that propagate logic from inputs to outputs. Any feedback from a cell’s transitive fanout back to an input creates a combinational loop that must be broken to reach a steady state. Although the Palladium XP loop breaking algorithm works correctly, the timed cells provided a unique challenge that led to unpredictable results.  Thus, a process was developed to ensure predictable loop breaking behavior. The user input to the process was to provide a property at the loop origin that the netlister recognized and translated to the appropriate loop breaking directives.

Augmented Netlisting

Ease of use and flow automation were two primary considerations in creating a solution that could be deployed more broadly. That made creating a one-step netlisting process a high-value item. The signal point annotation and automatic hierarchy expansion of the “digital timing” parameter helped achieve that goal. The netlister was enriched to identify the key schematic annotations at any point in the hierarchy, including bit and bus signals.

Consistency checking and annotation reporting created a log useful in debugging and evolving the solution.

Wrapper Cell Modeling and Verification

The netlister generates a list of schematic instances at the designated “netlister stop level” for each instance the requires a Verilog model with fine resolution timing. For the design in this paper there were 160 such instances.

The library of timed cells was created; these cells were actually “wrapper” cells comprised of the primitives for timed cell modeling described above. A new verification flow was created that used the behavior of the primitive cells as a reference for the expected behavior of the composed cells. The testing of the composed cells included had the timing width parameter set to 1 to enable direct comparison to the primitive cells. The Cadence Incisive Enterprise Simullator tool was successfully employed to perform assertion-based verification of the composed cells versus the existing primitive cells.

Mapping and Long Paths

Initial experiments showed that inclusion of the fine resolution timed cells into the digital emulation environment would about double the required capacity per run. As previously pointed out, the timed cells having only combinational forward paths creates a loop issue. This fact also had the result of creating some such paths that were more than 5,000 steps of logic. A timed cell optimization process helped to solve this problem. The basic idea was to break the path up by adding flip-flops in strategic locations to reduce combinational path length. The reason that this is important is that the maximum achievable emulation speed is related to combinational path length.

Results

Once the flow was in place, and some realistic test cases were run through it, some further performance tuning opportunities were discovered to additionally reduce runtimes (e.g., Palladium XP tbrun mode was used to gain speed). The reference used for overall speed gains on this solution was versus a purely software-based solution on the highest performance workstation available.

The findings of the performance comparison were startlingly good:

• On Palladium XP, the simulation speed is 50X faster than on Advantest’s fastest workstation

• Software simulation running 25 days can now be run in 12 hours -> realistic runtime enables long-running tests that were not feasible before

• Now have 500 tests that execute once in more than 48 hours

• They can be run much more frequently using randomization and this will increase test coverage dramatically

Steve Carlson

This blog discusses key features of concurrently editing a hierarchical cellview.(read more)

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