Enhancing FPGA Testing Efficiency: A PRBS-Based Approach for DSP Slices and Multipliers

Enhancing FPGA Testing Efficiency: A

The Built-In Self-Test (BIST) techniques are essential in the field of digital circuit design to ensure the reliable and efficient operation of complex components like multipliers.Multipliers play a pivotal role in numerous applications, including signal processing, arithmetic calculations, and data compression.It's crucial to verify their correctness and robustness under various conditions.One effective approach for testing multipliers is to employ a Pseudo-Random Binary Sequence (PRBS) generator and checker-based BIST methodology.Multipliers are fundamental components used for performing arithmetic operations in digital systems.They calculate products of binary numbers, which are essential in various computational tasks.Ensuring the correctness of multipliers is vital to maintain the integrity of digital systems.BIST is a methodology that enables digital circuits to test and verify their functionality autonomously without external test equipment.BIST techniques are designed to enhance the reliability and ease of testing complex digital circuits.PRBS is a deterministic sequence of binary values that exhibits properties similar to random sequences.PRBS generators produce sequences of 1s and 0s that appear random but are generated based on a specific algorithm.These sequences are commonly used in testing and data communication to ensure robustness and thorough coverage.A PRBS generator is used to produce a pseudorandom binary sequence.This sequence is fed as one of the inputs to the multiplier under the test.The other input(s) may consist of fixed values or additional PRBS sequences to cover various input patterns.Multiplier under Test is the digital multiplier that requires testing.It could be a standalone multiplier or part of a more extensive digital system.The PRBS checker receives the output from the multiplier under test.It compares this output with the expected PRBS sequence that should result from the given inputs.If the output matches the expected sequence, it indicates correct operation.Any discrepancies suggest a fault or error in the multiplier.PRBS sequences offer comprehensive coverage of input patterns, making it effective in detecting various faults.PRBS sequences exhibit random characteristics, enabling the detection of faults that might be missed by deterministic test vectors.The BIST technique can be automated, reducing the need for external test equipment and simplifying the testing process.Developing robust PRBS generators and checkers is crucial to the success of this BIST approach.Ensuring proper synchronization between the PRBS generator and checker can be challenging.The PRBS generator and checker-based BIST approach provides an efficient and reliable method for testing multipliers in digital circuits.It leverages the power of PRBS sequences to thoroughly test the multiplier's functionality and detect potential faults, ultimately contributing to the overall reliability and performance of digital systems [1]- [15].

░2. BLOCK DIAGRAM REPRESENTATION
Figure.1 consists of PRBS generator, DUT, and PRBS checker which are the major components of BIST.A PRBS (Pseudo-Random Binary Sequence) generator is a crucial component in Built-In Self-Test (BIST) systems used for testing digital circuits.PRBS sequences are deterministic binary sequences that appear random, making them valuable for testing a circuit's functionality and fault detection.In BIST, a PRBS generator generates these sequences to stimulate the circuit under test.The DUT is the target of the testing process, and the BIST system is designed to verify the functionality.The PRBS checker is responsible for assessing the quality and correctness of the received data stream.It compares the incoming data against a reference PRBS sequence to detect errors, assess signal integrity, and determine the link's performance.systems is a technique used to reduce the volume of test data that needs to be generated, stored, and transmitted during the testing of digital circuits.Compressing test data can help improve testing efficiency, reduce memory requirements, and enable faster testing, especially in high-complexity circuits.The "compare" and "analyze" are two distinct steps in the testing process that help identify and diagnose faults or defects within the tested electronic component or system.In the context of Built-In Self-Test (BIST) and digital circuits, a "ROM block" typically refers to a Read-Only Memory block.A ROM is a digital circuit component that stores data in a non-volatile manner, meaning the data remains intact even when the power is turned off.ROMs are used for various purposes in digital systems, including data storage, code storage, and as lookup tables for digital functions.The control block" is a critical component responsible for managing and coordinating various aspects of the BIST process.The control block plays a pivotal role in the initiation, execution, and control of tests on the circuit under evaluation.The integration of GTH transceivers, a product of Xilinx embedded within the Ultrascale FPGA and Zynq Ultrascale+ MPSoC families, heralds a new era in high-speed serial communication capabilities.Designed to cater to the demands of modern applications such as high-speed data transfer and interfacing with protocols like PCIe and Ethernet, these transceivers offer a versatile set of functionalities.Among them, the inclusion of runtime PRBS data control proves to be a pivotal feature.This dynamic control mechanism allows for continuous monitoring during operation, facilitating error detection and correction to ensure the robustness of data transfer.In Near-end Loopback (NEL) mode, the transceiver's ability to send PRBS patterns to its own receiver enables localized testing and self-diagnosis, while Far-end Loopback (FEL) mode extends testing capabilities to the entire communication link, including external components.The runtime PRBS data control emerges as a crucial tool for performance verification, remote testing, and dynamic debugging, empowering engineers to optimize the functionality of GTH transceivers in diverse scenarios.
In practical terms, runtime PRBS data control for GTH transceivers transforms the testing landscape for high-speed communication systems.In Near-end Loopback (NEL) mode, the transceiver's self-contained testing capabilities streamline the process of identifying and diagnosing issues within its own components.This localized testing proves invaluable for swift debugging without external dependencies.Conversely, in Farend Loopback (FEL) mode, the capability to send PRBS patterns to a remote transceiver facilitates comprehensive endto-end testing, offering insights into the performance of the entire communication link, including external elements like cables.The dynamic nature of the PRBS data control empowers engineers to adapt testing scenarios in real-time, providing a flexible approach to debugging and troubleshooting.
Consequently, the runtime PRBS data control emerges as a linchpin for ensuring the reliability, performance, and adaptability of GTH transceivers in the ever-evolving landscape of high-speed communication applications.

Figure. 4. GTH transceivers
Figure 5 represents a series-parallel PRBS-7 (Pseudo-Random Binary Sequence) generator is a combination of two types of shift registers: a series shift registers and a parallel shift register.Fig. 6 represents the proposed PRBS checker consisting of a PRBS generator, DUT, clock data recovery, error detection unit, comparator, BER, synchronization detection block, reference PRB sequence, and control logic unit.
Error detection unit includes the PRBS generator, which generates the next seed and compares with the in-coming seed.Depending on the comparison result it counts the error in data.It also counts the errors in Bits.A hybrid multiplier is used in the design to do multiplication for high speed received data.The proposed hybrid multiplier introduces a novel design concept by combining two distinct types of multipliers-Wallace and Vedic multipliers.This innovative approach aims to address the evolving requirements of modern computing systems, emphasizing the need for low-power consumption, reduced area, and minimal delay in multiplier operations [17].To further enhance the efficiency of the hybrid multiplier, a carry look ahead adder is employed.This addition aims to reduce carry propagation delay, a critical factor in multiplier performance.This PRBS provides flexibility to select different pattern length using a multiplexer in runtime.Along with the PRBS the multiplexer is also connected to user data, whereas the inbuilt PRBS option doesn't support this feature.

RESULTS AND DISCUSSIONS
Table 1 represents the resource utilization, revealing intriguing insights.The Proposed Design utilized more lookup tables (LUTs) and flip-flops, indicating potentially more complex logic.However, the Reference Design made more extensive use of Block RAMs, while both designs equally utilized Gigabit Transceivers (GT).The Proposed Design boasted slightly lower latency and integrated customized PRBS, indicating a versatile approach.The figures referenced in the information likely provide visual representations of the experimental setup and results, adding valuable context to this comparison.The provided information presents a comprehensive comparison between a "Reference Design" and a "Proposed Design" for an IP-based transmission loopback system employing PRBS (Pseudorandom Binary Sequence) generator and checker.In Table I, various key parameters were evaluated.Notably, the Proposed Design, which utilizes more advanced 16nm technology, displayed promising improvements.It operated at a slightly lower supply voltage, indicating enhanced power efficiency.Despite a significantly lower clock frequency of 156.25 MHz, the Proposed Design achieved a higher data rate (12.3125Gbps) and exhibited lower worst-case jitter (0.576 ps).Additionally, it consumed less power under nominal conditions.Conversely, the Reference Design excelled in supporting a higher maximum data rate of 13 Gbps in its PRBS checker.

░4. CONCLUSION
The research findings, coupled with the supplementary results, underscore the substantial advancements offered by the proposed hybrid multiplier in the FPGA landscape.This innovative approach, enriched with integrated BIST and PRBS capabilities, emerges as a formidable solution.The data reveals a noteworthy reduction in DSP slice utilization from 16% to a mere 5%, a substantial achievement.This liberated computational resource, within the FPGA, can be redirected to address other complex tasks, significantly enhancing the device's overall efficiency.The runtime control feature for PRBS data types at the block level design not only ensures adaptability but also aligns with the dynamic needs of modern digital systems development.Additionally, future work could delve into optimizing the hybrid multiplier's performance in scenarios involving real-time constraints or exploring its potential applicability in different FPGA architectures.Further refinement of the runtime control feature for PRBS data types and its adaptability to diverse digital system requirements could enhance the versatility of the proposed solution.

Figure. 1 .Figure 2
Figure. 1. Major components of BIST Figure 2 comprises of the "judge" component as a critical part of the BIST process as it determines the effectiveness of the self-test and provides information about the condition of the tested component or system.It plays a key role in identifying and diagnosing faults, which is essential for maintaining the reliability and functionality of electronic systems.Figure 2 also comprises a test vector generator as a critical component used in digital circuit design and semiconductor manufacturing.Its primary function is to generate a set of test patterns or vectors that are applied to the circuit under test to check for faults, verify functionality, and ensure the circuit's correctness.Another major component is the "Design under Test" (DUT) refers to the specific digital circuit or component that is being Figure 2 comprises of the "judge" component as a critical part of the BIST process as it determines the effectiveness of the self-test and provides information about the condition of the tested component or system.It plays a key role in identifying and diagnosing faults, which is essential for maintaining the reliability and functionality of electronic systems.Figure 2 also comprises a test vector generator as a critical component used in digital circuit design and semiconductor manufacturing.Its primary function is to generate a set of test patterns or vectors that are applied to the circuit under test to check for faults, verify functionality, and ensure the circuit's correctness.Another major component is the "Design under Test" (DUT) refers to the specific digital circuit or component that is being

Figure. 2 .
Figure. 2. Conventional Structure of BIST Figure 3 comprises of a PRBS (Pseudorandom Binary Sequence) generator-checker pair is commonly used in SERDES (Serializer/Deserializer) transceivers for testing and validating the functionality and performance of high-speed serial data communication links.

Figure 4
Figure 4 comprises of GTH transceivers, developed by Xilinx, are part of their Ultrascale FPGA and Zynq Ultrascale+ MPSoC families.These transceivers are designed to provide high-speed serial communication capabilities for applications such as highspeed data transfer and interface protocols like PCIe and Ethernet.GTH transceivers offer various modes of operation, including Near-end Loopback (NEL) and Far-end Loopback (FEL) modes, which are used for testing and debugging purposes.

Figure. 6 .
Figure. 6. Proposed PRBS checker Multiplier used in FPGA with proposed Hybrid multiplier.•The multiplier also has BIST and PRBS inbuilt.•The results show advantage in terms of DSP slice utilization from 16% to 5%, providing the DSP blocks available for other application/operation.

Figs. 7 Figure. 7 (Figure. 8
Figs.7(a)  and (b) represent the bits applied in order of 1011, errors to the order of 10-10 for proposed PRBS with hybrid multiplier and pf the order 10-2 for standard multiplier with inbuilt PRBS.The variation clearly shows the advantage of proposed PRBS-Multiplier in terms of Bit Error Rate.░Table 1: Comparison of resource utilization

Figure. 8 .
Figure. 8. Hybrid multiplier the PRBS is added as IP in block level design, which gives run time feature to control the PRBS type data to be applied.

Figure. 9 .
Figure. 9. Major components of PRBS-BIST Figure.10 represents the "ILA View of all RX-TX signals, showing data type and latency" refers to utilizing an Integrated Logic Analyzer (ILA) to monitor data transmission and reception signals.The ILA captures these signals, while also identifying their data type, such as binary or ASCII, and measuring latency, which is the time it takes for data to travel from the transmitter to the receiver.This analysis is crucial for assessing timing performance, ensuring data is transmitted and received within expected timeframes, and gaining insights into Figure.11 represents the hardware manager displays BER injection and loopback mode options."Inject" allows controlled bit error introduction, while "0-external loopback mode" signifies data sent externally for testing.Figure.8 represents the hybrid multiplier design with PRBS as block-level IP, offering runtime PRBS data control for testing flexibility.

Figure. 10 :
Figure.10: ILA View of all RX-TX signals, showing data type and latency

Figure. 11 :
Figure.11: Hardware manager showing BER (Inject option) and loopback mode(0-external loopback mode) for Hard PRBS available in Xilinx IP