Shift right (shift_right_xs)

Right shift all input sample values.

Design

Separately right shifts the bit values of the real and imaginary values of a complex value. Upper bit positions are padded with the most significant bit to preserve the sign of the number. Equivalent to a division by a power of 2.

The mathematical representation of the implementation is given in (79).

(79)\[y[n] = \lfloor x[n]/2^N \rfloor\]

In (79):

  • \(x[n]\) is the input values.

  • \(y[n]\) is the output values.

  • \(N\) is the number of bits the input is right shifted by.

A block diagram representation of the implementation is given in Figure 67:.

Block diagram outlining shift right implementation.

Figure 67: Shift right implementation.

The real and imaginary inputs are treated as separate value streams (i.e. (79) / Fig. 67 will be implemented twice within the component, once for the real values and a second time for the imaginary values).

Interface

<?xml version="1.0"?>
<componentspec>
  <property name="shift" type="uchar" parameter="true" default="1" writable="false" description="Number of bit positions the input values will be right shifted by."/>
  <port name="input" producer="false" protocol="complex_short_timed_sample-prot"/>
  <port name="output" producer="true" protocol="complex_short_timed_sample-prot"/>
</componentspec>

Ports

Inputs:

  • input: Primary input samples port.

    • Protocol: complex_short_timed_sample-prot

    • Optional: False

Outputs:

  • output: Primary output samples port.

    • Protocol: complex_short_timed_sample-prot

    • Optional: False

Opcode handling

Only values in a sample opcode message are right shifted. All other opcodes messages received are passed through this component without any effect.

Properties

  • shift: Number of bit positions the input values will be right shifted by.

    • Type: uchar

    • Access:

      • Parameter: True

      • Writable: False

      • Initial: False

      • Volatile: False

    • Default value: 1

Parameters

Implementations

Example application

<?xml version="1.0"?>
<application done="file_write">
  <instance component="ocpi.core.file_read" connect="shift_right_xs">
    <property name="filename" value="input.bin"/>
  </instance>
  <instance component="ocpi.comp.sdr.math.shift_right_xs" connect="file_write">
    <property name="shift" value="3"/>
  </instance>
  <instance component="ocpi.core.file_write">
    <property name="filename" value="output.bin"/>
  </instance>
</application>

Dependencies

The dependencies to other elements in OpenCPI are:

  • None.

There is also a dependency on:

  • ieee.std_logic_1164

  • ieee.numeric_std

Limitations

Limitations of shift_right_xs are:

  • None.

Testing

Component testing not completed.