Ping-Pong Buffer

The fundamental structure consists of two identical memory banks that alternate roles. While Bank A is actively being written with incoming data from an ADC or sensor, Bank B is simultaneously being read and processed by a DSP or neural network accelerator. This spatial separation of read and write operations eliminates the need for complex arbitration logic and prevents read-write hazards. The two banks are typically implemented using Block RAM (BRAM) in FPGAs or dual-port SRAM in ASICs, allowing true simultaneous access without clock cycle stealing.

The transition between banks is accomplished by swapping a pointer or base address register rather than physically moving data. This pointer flip operation completes in a single clock cycle, creating an instantaneous handoff with zero latency overhead. The mechanism typically uses a multiplexer controlled by a frame synchronization signal:

• A buffer_sel signal toggles on each complete frame
• The write DMA engine targets one address range while the read engine targets the other
• No data is ever copied between banks, preserving memory bandwidth and power

Ping-pong buffering provides a fixed, predictable processing latency equal to exactly one buffer depth. This deterministic latency is critical for phase-coherent, multi-channel applications such as beamforming and direction finding. The total system delay from ADC sample to processed output is:

• Latency = N/Buffer_Depth + Processing_Time
• The buffer depth is chosen based on the FFT size or neural network frame length
• Jitter is eliminated because the processing engine always operates on a complete, contiguous frame
• This contrasts with circular buffers, which introduce variable latency depending on fill level

The architecture inherently decouples the producer and consumer clock domains, enabling backpressure-free operation. The input side can write at its native sample rate while the output side reads at the processing clock rate, with the buffer absorbing any instantaneous rate mismatch. Key benefits include:

• No stall cycles inserted into the ADC sample pipeline
• The processing engine never waits for data; it always has a complete frame ready
• Clock domain crossing is handled at the buffer boundary using dual-clock FIFOs or synchronized control signals
• This decoupling is essential for wideband systems where the ADC runs at multiple GSPS while the DSP operates at a lower FPGA fabric clock

The buffer swap is synchronized to a frame trigger that defines the boundary of a coherent processing interval. This trigger may be derived from:

• A GPS-disciplined 1 PPS signal for distributed spectrum sensing
• An internal timer for fixed-duration FFT frames
• An external event such as a pulse detection in radar applications
• The swap occurs only on frame boundaries, ensuring that each processing frame contains a contiguous, non-overlapping segment of the input signal. This prevents spectral leakage artifacts that would occur if FFT windows spanned across buffer boundaries.

In modern FPGA designs, ping-pong buffers are commonly implemented using AXI4-Stream interfaces with DMA engines. A typical Xilinx or Intel FPGA implementation uses:

• A VDMA (Video DMA) or custom scatter-gather DMA configured for double buffering
• The tlast signal on the AXI4-Stream interface marks the end of a frame and triggers the buffer swap
• High-Level Synthesis (HLS) tools can automatically infer ping-pong behavior from PIPELINE and DATAFLOW pragmas
• The buffer memory is partitioned using array_partition directives to map each bank to separate BRAM primitives, enabling true dual-port access