dsd_x16 HDL Worker

16-channel time-shared differential detector and adaptive soft quantizer; converts complex symbol pairs into channel-tagged 3-bit soft decisions with an accompanying 16-bit wide soft value for sync correlation.

Detail

The dsd_x16 RTL architecture (rtl of worker) uses a 3-stage feed-forward pipeline across three clocked processes:

Stage 0 — differential products (``p_in``). On a sample beat (in_beat and complex_short_timed_sample_sample_op_e), two 16x16 signed multipliers compute:

• qi_prod = Q(n) * I_prev(ce) (Q of current, I of stored previous)

• iq_prod = I(n) * Q_prev(ce) (I of current, Q of stored previous)

I_prev and Q_prev are immediately updated to the current symbol so they are ready for the next symbol on the same channel. The channel index ce is carried forward through a 3-entry ch_p / vld_p pipeline that advances only on in_beat, providing stall-safe tag propagation.

Stage 1 — imaginary subtraction (``p_in``, same process, second clock). imag_diff <= qi_prod - iq_prod (33-bit signed, 1-bit growth). This is the imaginary part of x(n) * conj(x(n-1)).

Stage 2 — negation, magnitude tracking, and quantization (``p_quant``). Fires when in_beat = '1' and vld_p(2) = '1':

1. soft_n = -(imag_diff[32:17]) — top 16 bits of the 33-bit diff, negated (polarity convention from msk_demod.vhd). Q-format: this is effectively Q0.15 relative to the input Q1.14 symbols from ted_x16.

2. mag = |soft_n| (absolute value, 16-bit unsigned).

3. IIR update: mag_acc(ce) <= mag_acc(ce) - (mag_acc(ce) >> 8) + mag. The mean = mag_acc[23:8] (16-bit) uses the old accumulator so the shift computation and the update are in the same clock cycle without feedback.

4. Shift selection: scan mean from MSB to find its leading-one position k; shft = max(0, k - (OUT_W - 2)) = max(0, k - 1).

5. shifted = shift_right(soft_n, shft) (signed arithmetic shift).

6. Saturate shifted to [-3, +3] (signed 3-bit).

7. Push to output FIFO: 36-bit word ch_p(2)[3:0] & soft_n[15:0] & sat_ext[15:0] where sat_ext is the 3-bit quantized soft sign-extended to 16 bits.

Output word packing (bits of the 32-bit output sample):

Output FIFO and FSM. A 64-entry x 36-bit internal FIFO decouples the quantizer from the WSI output. The output FSM (states OST_IDLE, OST_M0–OST_M3, OST_S, OST_EOF) emits one 5-beat tagged message per symbol: four metadata beats (OST_M0–OST_M3) with the channel id in word 2 bits [3:0], then one sample beat (OST_S) with the packed soft word. Backpressure from the downstream port is honoured on every beat via output_in.ready.

Latency. From an accepted input sample beat to the corresponding FIFO push: 3 clock cycles (stages 0, 1, and 2 each consume one clock). From FIFO push to first output beat: variable (depends on output port availability and FIFO drain state), but bounded because input is stalled when the FIFO occupancy reaches FIFO_DEPTH - 4 = 60.

Reset. rst is asserted on either ctl_in.reset or a pulse on the init property. All per-channel state arrays (i_prev, q_prev, mag_acc, symcnt), the pipeline registers, and the FIFO pointers are cleared synchronously.

Worker Properties

• ocpi_buffer_size_output

  • Type: ushort

  • Access:

    • Parameter: False

    • Writable: False

    • Initial: True

    • Volatile: False

    • Read back: False

  • Default value: 0

• ocpi_blocked_output

  • Type: ulong

  • Access:

    • Parameter: False

    • Writable: False

    • Initial: False

    • Volatile: True

    • Read back: False

  • Default value: None

• ocpi_max_latency_output

  • Type: ushort

  • Access:

    • Parameter: True

    • Writable: False

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: None

• ocpi_latency_output

  • Type: ushort

  • Access:

    • Parameter: False

    • Writable: False

    • Initial: False

    • Volatile: True

    • Read back: False

  • Default value: None

• ocpi_messages_output

  • Type: ulong

  • Access:

    • Parameter: False

    • Writable: False

    • Initial: False

    • Volatile: True

    • Read back: False

  • Default value: None

• ocpi_bytes_output

  • Type: ulong

  • Access:

    • Parameter: False

    • Writable: False

    • Initial: False

    • Volatile: True

    • Read back: False

  • Default value: None

Worker Ports

Inputs:

• input

  • Protocol: complex_short_timed_sample

  • Optional: False

Outputs:

• output

  • Protocol: complex_short_timed_sample

  • Optional: False

Worker Ports

Inputs:

• input:

  • Type: StreamInterface

  • Protocol: complex_short_timed_sample-prot

  • ClockDirection: in

  • Data width: 32

Outputs:

• output:

  • Type: StreamInterface

  • Protocol: complex_short_timed_sample-prot

  • Worker EOF: true

  • Clock: input

  • Data width: 32

Utilisation

Utilization reporting is not currently implemented.