Musings, Courses, & Projects by Rob Marano

Notes for Week 1

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Topics

1. Intro to logic design using Verilog HDL
2. Logic elements
3. Expressions
4. Modules and ports

Topics Deep Dive

Gate-Level Modeling

Introduction:

• Introduction to SystemVerilog and its benefits for hardware description.
• Basic syntax, data types (e.g., wire, reg, logic), and operators.
• Simple gate primitives (e.g., and, or, not, xor).
• Modeling combinational logic circuits using gate primitives.
• Hands-on lab: Implement basic gates and simple combinational circuits (e.g., half-adder, full-adder).

SystemVerilog for testbench development:

• Generating input stimuli using random variables.
• Monitoring and checking output signals.
• Using scoreboards for data comparison.
• Hands-on lab: Develop a basic testbench for a design

What is bit swizzling?

• Bit swizzling is a technique for rearranging the order of bits within a binary data structure, such as a byte, word, or vector.
• It involves extracting specific bits from their original positions and placing them into new positions within another data structure.

Here’s a breakdown of bit swizzling:

Purpose:

• Data Reorganization: Bit swizzling is often used to reorganize data to match specific hardware requirements or to optimize data structures for certain algorithms.
• Endianness Conversion: Converting between big-endian and little-endian representations of data involves swizzling bits.
• Cryptography: Swizzling bits can be used in cryptographic operations to obscure data patterns.
• Image Processing: Manipulating individual bits in image data for tasks like color transformations or image filtering.
• Error Correction: Rearranging bits for error detection and correction codes.

Techniques:

• Shifting: Shifting bits left or right («, ») to move them to new positions.
• Masking: Using bitwise AND (&) to isolate specific bits.
• Concatenation: Combining bits from different sources using concatenation operators ({ }).
• Replication: Repeating specific bits or patterns.

For Example:

Let’s say you have a 4-bit data structure 1011 and you want to swap the two middle bits.

You could achieve this through swizzling:

1. Isolate the middle bits:
   1. Mask the first and last bits with 0011 to get 0011.
2. Swap the middle bits:
   1. Shift the isolated bits left by one (0110) and right by one (0011).
   2. Combine the shifted results using OR (|) to get 0111.
3. Combine with the original outer bits:
   1. Mask the original data with 1001 to get 1001.
      1. Combine this with the swapped middle bits using OR (|) to get the final result 1111.

SystemVerilog Support:

SystemVerilog provides powerful bit swizzling capabilities:

• Concatenation: Use the concatenation operator { and } to combine bits in any desired order.
• Replication: Specify the number of times to repeat a bit or pattern within the concatenation.
• Indexed Part-Select: Extract a specific range of bits using indexed part-select ([start_bit:end_bit]).

Example in SystemVerilog:

logic [7:0] data = 8'b10110100;
logic [7:0] swizzled_data;

swizzled_data = {data[6:7], data[2:3], data[4:5], data[0:1]}; // Swizzle specific bits

Bit swizzling is a fundamental technique in computer architecture and digital design, enabling efficient data manipulation and optimization at the bit level.

More complex gate-level modeling:

• Using assign statements for continuous assignments.
• Hierarchical design and module instantiation.
• Introduction to testbenches and basic verification concepts.
• Hands-on lab: Build a more complex combinational circuit (e.g., multiplexer, decoder) using hierarchy.

Introduction to sequential logic:

• Flip-flops (e.g., DFF, JKFF) and latches.
• Modeling simple sequential circuits (e.g., counters, shift registers).
• Understanding the concept of clocking and timing in simulations.
• Hands-on lab: Implement a simple counter or shift register.

Advanced gate-level modeling:

• User-defined primitives (UDPs) for custom gate definitions.
• Delays in gate-level modeling (#delay).
• Introduction to always blocks for procedural assignments.
• Hands-on lab: Design a sequential circuit with custom gate delays and verify its behavior.

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