Queue

Store inputs in FIFO register

• 

Libraries:
DSP System Toolbox / Signal Management / Buffers

Description

The Queue block stores a sequence of input samples in a first-in first-out (FIFO) register. Depending on the inputs at the ports, the block can push, pop, or empty the queue.

When the block receives a trigger event at the Push port, it pushes the input at the In port to the end of the queue. When the block receives a trigger event at the Pop port, it pops the first element off the queue and holds the Out port at that value. The first input to be pushed onto the queue is always the first to be popped off.

Examples

Queues

Push and pop elements from a queue using a Queue block with a system of selection switches.

• Open Model

Ports

Input

In — Input to FIFO register

scalar | vector | matrix

Specify the input to the FIFO register as a scalar, vector, or a matrix.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean | fixed point

Push — Trigger signal to push queue

scalar

Specify the trigger signal to push the queue as a real scalar.

Input to the Push port must have the same data type as the input to the Pop and Rst ports.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean

Pop — Trigger signal to pop queue

scalar

Specify the trigger signal to pop the queue as a real scalar.

Input to the Pop port must have the same data type as the inputs to the Push and Rst ports.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean

Rst — Trigger signal to empty queue

scalar

Specify the trigger signal to empty the queue as a real scalar.

Input to the Rst port must have the same data type as the inputs to the Push and Pop ports.

Dependencies

To enable this port, select Show reset port (Rst) to clear internal stack buffer.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean

Output

Out — Output of FIFO register

scalar | vector | matrix

Output of the FIFO register, returned as a scalar, vector, or a matrix.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean | fixed point

Empty — Indicates if queue is empty

1 | 0

The block returns 1 at this port to indicate an empty queue and 0 otherwise.

Dependencies

To enable this port, select Show empty register indicator port (Empty).

Data Types: double | Boolean

Full — Indicates if queue is full

1 | 0

The block returns 1 at this port to indicate a full queue and 0 otherwise.

If you select Dynamic reallocation in the Push onto full register parameter, the Full port remains 0.

Dependencies

To enable this port, select Show full register indicator port (Full).

Data Types: double | Boolean

Num — Track number of elements in queue

scalar

Track the number of elements in the queue at any given time.

If the data type at the In port is double, the data type at the Num port is double. Otherwise, the data type at the Num port is uint32.

Dependencies

To enable this port, select Show number of register entries port (Num).

Data Types: double | uint32

Parameters

Register size — Number of entries FIFO register can hold

8 (default) | positive integer

The number of entries that the FIFO register can hold, specified as a positive integer.

Trigger type — Type of trigger event for Push, Pop, and Rst ports

Rising edge (default) | Falling edge | Either edge | Non-zero sample

The type of event that triggers the execution of the block. Select one of these options:

Trigger Type	Description
Rising edge	Triggers execution of the block when the trigger input does one of the following: Rises from a negative value to zero or a positive value. Rises from zero to a positive value but is not a continuing rise.
Falling edge	Triggers execution of the block when the trigger input does one of the following: Falls from a positive value to zero or a negative value. Falls from zero to a negative value but is not a continuing fall.
Either edge	Triggers execution of the block when the trigger input type is Rising edge or Falling edge (as described above).
Non-zero sample	Triggers execution of the block at each sample time that the trigger input is not zero.

The rate of the trigger signal must be the same as the rate of the data signal input.

Push onto full register — Specify block behavior to push request when register is full

Dynamic reallocation (default) | Ignore | Warning | Error

Specify the block behavior when it receives a trigger at the Push port but the register is full. The available options are:

• Dynamic reallocation — Dynamically resize the register to accept as many additional inputs as memory permits.

  To use this option, set the System target file parameter on the Code Generation pane of the Model Configuration Parameters dialog box to grt_malloc.tlc – Generic Real-Time Target with dynamic memory allocation.

  Note

  If your model contains any referenced models that use a Queue block with the Push onto full register parameter set to Dynamic reallocation, you cannot simulate your top-level model in the accelerator mode in Simulink^®.

• Ignore — Ignore the trigger event and continue the simulation.

• Warning — Ignore the trigger event but display a warning message in the MATLAB^® Command Window.

• Error — Display an error dialog box and terminate the simulation.

Note

The Push onto full register is a diagnostic parameter. Like all diagnostic parameters in the Configuration Parameters dialog box, this parameter is set to Ignore in the code generated for this block by the Simulink Coder™ code generation software.

Pop empty register — Specify block behavior to pop request when register is empty

Warning (default) | Ignore | Error

Specify the block behavior when it receives a trigger at the Pop port but the register is empty. The available options are:

• Ignore — Ignore the trigger event and continue the simulation.

• Warning — Ignore the trigger event but display a warning message in the MATLAB Command Window.

• Error — Display an error dialog box and terminate the simulation.

Note

The Pop empty register is a diagnostic parameter. Like all diagnostic parameters in the Configuration Parameters dialog box, this parameter is set to Ignore in the code generated for this block by the Simulink Coder code generation software.

Show empty register indicator port (Empty) — Enable Empty output port

off (default) | on

Select to enable the Empty output port to indicate an empty register.

Show full register indicator port (Full) — Enable Full output port

off (default) | on

Select to enable the Full output port to indicate a full register.

Show number of register entries port (Num) — Enable Num output port

off (default) | on

Select to enable the Num output port to show the number of register entries.

Show reset port (Rst) to clear internal stack buffer — Enable Rst input port

off (default) | on

Select to enable the Rst input port. The block empties the queue when it receives a trigger at this port.

Clear output port on reset — Set Out port to 0 when clearing queue

off (default) | on

If you select Clear output port on reset, then a trigger event at the Rst port empties the queue and sets the value at the Out port to 0. This setting also applies when a disabled subsystem containing the Queue block is re-enabled.

Dependencies

To enable this parameter, select the Show reset port (Rst) to clear internal stack buffer parameter.

Allow direct feedthrough — Allow input data to be readily available at Out port

on (default) | off

Select to allow the input data to be available immediately at the Out port of the block. Clear to delay the input data by an extra frame.

When you select the Allow direct feedthrough parameter and trigger two or more of the control input ports at the same time step, the block executes the operations in the following order:

1. Reset

2. Push

3. Pop

When you clear the Allow direct feedthrough parameter and trigger two or more of the control input ports at the same time step, the block executes the operations in the following order:

1. Reset

2. Pop

3. Push

The rate of the trigger signal must be the same as the rate of the data signal input.

Block Characteristics

Data Types	Boolean | double | fixed point | integer | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

More About

Operation of Queue Block

This table shows how the Queue block operates when you set the Register size to 4, Trigger type to Either edge, and enable the Clear output port on reset parameter. Because the block triggers on both rising and falling edges, each transition from 1 to 0 or 0 to 1 in the Push, Pop, and Rst columns represents a distinct trigger event. 1 in the Empty column indicates an empty queue, while 1 in the Full column indicates a full queue.

In	Push	Pop	Rst	Queue	Out	Empty	Full	Num
1	0	0	0		0	1	0	0
2	1	0	0		0	0	0	1
3	0	0	0		0	0	0	2
4	1	0	0		0	0	0	3
5	0	0	0		0	0	1	4
6	0	1	0		2	0	0	3
7	0	0	0		3	0	0	2
8	0	1	0		4	0	0	1
9	0	0	0		5	1	0	0
10	1	0	0		5	0	0	1
11	0	0	0		5	0	0	2
12	1	0	1		0	0	0	1

In the last time step, there are triggers at the Push and Rst ports simultaneously. The Rst trigger takes precedence: the block first clears the queue and then pushes the value at the In port into the queue.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

The following limitations apply:

• Generated code relies on the memcpy or memset function (string.h) under certain conditions.

• When you select Dynamic reallocation, you must set the System target file parameter on the Code Generation pane of the Configuration Parameters dialog box to grt_malloc.tlc - Generic Real-Time Target with dynamic memory allocation.

Version History

Introduced before R2006a