Rivos Interview Questions and Answers

Q1. FSM and Rtl of sequence detector
Ans. 
Sequence detector is a digital circuit that detects a specific sequence of bits in a stream of input data.
• FSM (Finite State Machine) is commonly used to design sequence detectors.

• RTL (Register Transfer Level) describes the behavior of digital circuits using registers and logic gates.

• Example: A sequence detector that detects '1010' in a stream of binary data.

• Example: FSM states for this detector could be S0, S1, S2, S3 ...read more
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Q2. Sv oops, virtual function, polymorphism
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Q3. Testbench structure, functions of agent, sequencer, sequence, driver etc
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Q4. Factory and factory override
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Q1. What is the difference between stack and queue?
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Stacks and queues are data structures that manage collections of elements, differing in their order of access.
• Stack: Follows Last In First Out (LIFO) principle; the last element added is the first to be removed. Example: Undo functionality in text editors.

• Queue: Follows First In First Out (FIFO) principle; the first element added is the first to be removed. Example: Print job scheduling.

• Operations: Stacks use push (add...read more
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Q2. Draw the basic Inverter gate for CMOS?
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A CMOS inverter is a basic digital logic gate that inverts the input signal using complementary MOSFETs for efficient operation.
• Structure: A CMOS inverter consists of a PMOS transistor connected to the power supply and an NMOS transistor connected to ground.

• Operation: When the input is high, the NMOS turns on and PMOS turns off, pulling the output low; when the input is low, the opposite occurs.

• Power Efficiency: CMOS t...read more
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Q3. What is pipelining?
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Pipelining is a technique used in computer architecture to improve instruction throughput by overlapping execution stages.
• Instruction Overlap: Pipelining divides instruction execution into stages, allowing multiple instructions to be processed simultaneously.

• Stages of Execution: Common stages include Fetch, Decode, Execute, Memory Access, and Write Back, each handled in parallel for different instructions.

• Increased Thr...read more
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Q4. AHB and APB protocols and why we need a bridge?
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AHB and APB are AMBA protocols; a bridge connects them for compatibility and efficient communication in SoC designs.
• AHB (Advanced High-performance Bus): A high-speed bus protocol designed for high-bandwidth applications, supporting burst transfers.

• APB (Advanced Peripheral Bus): A simpler, low-power bus protocol used for connecting low-bandwidth peripherals, optimizing power consumption.

• Bridge Functionality: A bridge is...read more
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C++ on leetcode programming

Q1. Cpu branch predictor
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Q2. Cpu cache protocol
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Q1. How would you verify a last level cache?
Ans. 
Verify last level cache by running stress tests, analyzing cache hit/miss rates, and comparing performance metrics.
• Run stress tests to simulate high load scenarios and observe cache behavior

• Analyze cache hit/miss rates to ensure data is being efficiently stored and retrieved

• Compare performance metrics before and after cache verification to measure improvements

• Use tools like CacheGrind or Valgrind for detailed cache ana...read more
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Q2. Describe an important debug that you've done.
Ans. 
Identifying and fixing a race condition in a multi-threaded system
• Observed intermittent failures in test results

• Used debugging tools like gdb and log analysis to trace the issue

• Identified the root cause as a race condition between two threads

• Implemented a mutex lock to resolve the issue

• Verified the fix by running stress tests
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