decimate3 HDL Worker

HDL implementation of a frame-level integer decimator for the complex_short_timed_sample protocol, targeting 3:1 reduction of 12 SPS channelizer output to 4 SPS demodulator input.

Detail

The worker operates on complete 16-sample messages (frames) rather than on individual IQ words. With the default factor = 3, every third input message is forwarded verbatim and the intervening two are dropped.

Phase counter: frame_phase is an 8-bit counter, range 0..(factor-1). It increments by one on each input SOM beat and wraps to zero after reaching factor - 1. The fac integer variable is read from props_in.factor each clock edge and clamped to a minimum of 1 to guard against a zero write.

Forward decision:

• fwd_comb is the combinatorial keep signal for the current input word:

  fwd_comb = '1' when (som='1' and frame_phase=0)
                   or  (som='0' and fwd_reg='1')
             else '0'
  

• fwd_reg is the registered keep decision latched at each SOM. It is set to '1' when frame_phase = 0 (this message is to be kept) and to '0' otherwise. It remains stable through all 16 words of the message.

• Combining the SOM-case combinatorially with the non-SOM case via fwd_comb ensures the SOM word itself is forwarded without a one-cycle gap, giving clean SOM/EOM passthrough on kept messages.

Forwarding: when fwd_comb = '1', all output signals are driven directly from the corresponding input signals (data, opcode, byte-enable, SOM, EOM). When fwd_comb = '0', give and valid are held low so the output port sees no transaction. The worker always takes input (input_out.take <= input_in.ready).

EOF propagation: the eof_seen flag is set on the first cycle that input_in.eof is asserted and is held until reset. It is forwarded on output_out.eof combinatorially, so the EOF appears on the output in the same cycle it arrives on the input.

Latency: zero additional pipeline cycles for forwarded messages. Dropped messages contribute no latency. The fwd_reg register is set on the SOM cycle but is not needed until the second word of a kept message, so no additional delay is visible to the downstream consumer.

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.