Keep M in N

Decimate a stream, keeping the first M items out of every N starting after offset items.

Also see Keep 1 in N.

Parameters

(R): Run-time adjustable

Type

Supported types are: complex, float, int, short, and byte

M (R)

Number of items to take in block of items

N (R)

Block size in items

Initial Offset

Initial item offset into the stream

Example Flowgraph

Here is an example flowgraph using the Keep M in N Block. It has a vector source with values [1,2,3,4,5,6,7,8,9,10] repeating.

This flowgraph will not run for very long, because at some (soon) point, the "Qt GUI Time Sink" will run out of input, as the visualization sink consumes the same amount of itmes from each of its inputs. Now, to produce, say, 10000 items, the "Keep M in N" block will have to consume 10000×N/M items. With M < N (inherently!), that means that the "Keep M in N" block consumes only M items from the "Vectors Source" when the "Qt GUI Time Sink" consumes N. That means that the output buffer of the "Vector Source" gets consumed (emptied) only by M samples per N outputs of the "Keep M in N", but "Qt GUI Time Sink" needs all N (of N). So, that Source's output buffer gets "stuck at full", while the "Keep M in N"'s output buffer gets stuck at "empty", and the flow graph stalls.

The block parameters are set to:

This results in the following output:

Source Files

C++ files

keep_m_in_n_impl.cc]

Header files

keep_m_in_n_impl.h

Public header files

keep_m_in_n.h

Block definition

blocks_keep_m_in_n.block.yml