DescriptionQ1064
Q1064DesignArchAMDASIC interview problem
Build a Two-Bank Ping-Pong Frame Buffer
TechniquesDesignArchClocking
DifficultyMedium
TopicTiming
LanguageSystemVerilog
Requirements4 checkpoints
01
Problem
Input and output use the same clock. Every frame is exactly four accepted bytes. Two 4-byte banks allow the producer to fill one bank while the consumer drains the other. Completed frames must leave in arrival order. Implement bank ownership, atomic handoff, ready/valid backpressure, and fixed four-beat output framing.
Module declarationSystemVerilog
module pingpong4(input logic clk,rst_n,
input logic in_valid, output logic in_ready, input logic [7:0] in_data,
output logic out_valid, input logic out_ready, output logic [7:0] out_data,
output logic out_first,out_last);
// each input frame is exactly four accepted bytesExample input and output
Use this case to check your interpretationInput
Case 1: Input [1,2,3,4]
Case 2: Input frames [10,11,12,13] and [20,21,22,23]
Case 3: If output stalls on byte 12, `out_data=12`, `out_valid=1`, and both framing flagsOutput
Case 1: Must later output [1,2,3,4] with `out_first` only on 1 and `out_last` only on 4.
Case 2: May fill both banks before output starts, but must drain in that same frame order.
Case 3: Must remain stable; input may continue into the other free bank only.Explanation
The shown result follows by applying this rule: Ownership transitions are atomic and prevent simultaneous producer/consumer access to one bank. The cases also demonstrate this requirement: Deassert `in_ready` only when no bank is available for filling. Producer and consumer may access different banks in the same cycle but must never access the same bank concurrently.
02
Requirements (4)
- Track each bank as FREE, FILL, FULL, or DRAIN plus monotonically ordered frame ownership. Reset makes both banks free and clears all valid/framing outputs.
- Write one byte only on an input handshake. After the fourth byte, atomically mark that bank FULL; never expose a partially filled bank to the consumer.
- Drain the oldest FULL bank. Hold data, first, and last stable while stalled; after the fourth output handshake, atomically free the bank.
- Deassert `in_ready` only when no bank is available for filling. Producer and consumer may access different banks in the same cycle but must never access the same bank concurrently.