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Rate Transition

Handle transfer of data between blocks operating at different rates

  • Library:
  • Simulink / Signal Attributes

    HDL Coder / Signal Attributes

Description

The Rate Transition block transfers data from the output of a block operating at one rate to the input of a block operating at a different rate. Use the block parameters to trade data integrity and deterministic transfer for faster response or lower memory requirements. To learn about data integrity and deterministic data transfer, see Data Transfer Problems (Simulink Coder).

Transition Handling Options

Transition Handling OptionsBlock Parameter Settings
  • Data integrity

  • Deterministic data transfer

  • Maximum latency

Select:

  • Ensure data integrity during data transfer

  • Ensure deterministic data transfer

  • Data integrity

  • Nondeterministic data transfer

  • Minimum latency

  • Higher memory requirements

Select:

  • Ensure data integrity during data transfer

Clear:

  • Ensure deterministic data transfer

  • Potential loss of data integrity

  • Nondeterministic data transfer

  • Minimum latency

  • Lower memory requirements

Clear:

  • Ensure data integrity during data transfer

  • Ensure deterministic data transfer

Dependencies

The behavior of the Rate Transition block depends on:

Block Labels

When you update your diagram, a label appears on the Rate Transition block to indicate simulation behavior.

LabelBlock Behavior
ZOH Acts as a zero-order hold
1/z Acts as a unit delay
Buf Copies input to output under semaphore control
Db_buf Copies input to output using double buffers
3bufCopies input to output using triple buffers
Copy Unprotected copy of input to output
NoOp Does nothing
Mixed Expands to multiple blocks with different behaviors

The block behavior label shows the method that ensures safe transfer of data between tasks operating at different rates. You can use the sample-time colors feature (see View Sample Time Information) to display the relative rates that the block bridges. Consider, for example, the following model:

Sample-time colors and the block behavior label show:

  • The Rate Transition block at the top of the diagram acts as a zero-order hold in a fast-to-slow transition.

  • The Rate Transition block at the bottom of the diagram acts as a unit delay in a slow-to-fast transition.

For more information, see Handle Rate Transitions (Simulink Coder).

Effects of Synchronous Sample Times

The following table summarizes how each label appears when the sample times of the input and output ports (inTs and outTs) are periodic, or synchronous.

Block Settings

Block Label

Rate Transition

Conditions for Rate Transition Block

With Data Integrity and Determinism

With Only Data Integrity

Without Data Integrity or Determinism

inTs = outTs

(Equal)

inTsOffset < outTsOffset

None (error)

Buf

Copy or NoOp (see note that follows the table)

inTsOffset = outTsOffset

Copy or NoOp (see note that follows the table)

Copy or NoOp (see note that follows the table)

inTsOffset > outTsOffset

None (error)

Db_buf

inTs < outTs

(Fast to slow)

inTs = outTs / N

inTsOffset, outTsOffset = 0

ZOH

Buf

inTs = outTs / N

inTsOffsetoutTsOffset

None (error)

inTs = outTs / N

inTsOffset > outTsOffset

None (error)

Db_buf

inTsoutTs / N

None (error)

inTs > outTs

(Slow to fast)

inTs = outTs * N

inTsOffset, outTsOffset = 0

1/z

Db_buf

inTs = outTs * N

inTsOffsetoutTsOffset

None (error)

inTs = outTs * N

inTsOffset > outTsOffset

None (error)

inTsoutTs * N

None (error)

KEY

  • inTs, outTs: Sample times of input and output ports, respectively

  • inTsOffset, outTsOffset: Sample time offsets of input and output ports, respectively

  • N: Integer value > 1

When you select the Block reduction parameter on the Configuration Parameters dialog box, Copy reduces to NoOp. No code generation occurs for a Rate Transition block with a NoOp label. To prevent a block from being reduced when block reduction is on, add a test point to the block output (see Test Points in the Simulink documentation).

Effects of Asynchronous Sample Times

The following table summarizes how each label appears when the sample time of the input or output port (inTs or outTs) is not periodic, or asynchronous.

Block Settings

Block Label
With Data Integrity and DeterminismWith Only Data IntegrityWithout Data Integrity or Determinism

inTs = outTs

Copy

Copy

Copy

inTsoutTs

None (error)

Db_buf

KEY

  • inTs, outTs: Sample times of input and output ports, respectively

Ports

Input

expand all

Input signal to transition to a new sample rate, specified as a scalar, vector, matrix, or N-D array. To learn about the block parameters that enable you to trade data integrity and deterministic transfer for faster response or lower memory requirements, see Transition Handling Options.

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

Output

expand all

Output signal is the input signal converted to the sample rate you specify. The default configuration ensures safe and deterministic data transfer. To learn about the block parameters that enable you to trade data integrity and deterministic transfer for faster response or lower memory requirements, see Transition Handling Options.

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

Parameters

expand all

Selecting this check box results in generated code that ensures data integrity when the block transfers data. If you select this check box and the transfer is nondeterministic (see Ensure deterministic data transfer), depending on the priority of input rate and output rate, the generated code uses a proper algorithm using single or multiple buffers to protect data integrity during data transfer.

Otherwise, the Rate Transition block is either reduced or generates code using a copy operation to affect the data transfer. This unprotected mode consumes less memory. But the copy operation is also interruptible, which can lead to loss of data integrity during data transfers. Select this check box if you want the generated code to operate with maximum responsiveness (that is, nondeterministically) and data integrity. For more information, see Rate Transition Block Options (Simulink Coder).

Programmatic Use

Block Parameter: Integrity
Type: character vector
Values: 'off' | 'on'
Default: 'on'

Selecting this check box results in generated code that transfers data at the sample rate of the slower block, that is, deterministically. If you do not select this check box, data transfers occur when new data is available from the source block and the receiving block is ready to receive the data. You avoid transfer delays, thus ensuring that the system operates with maximum responsiveness. However, transfers can occur unpredictably, which is undesirable in some applications. For more information, see Rate Transition Block Options (Simulink Coder).

Programmatic Use

Block Parameter: Deterministic
Type: character vector
Values: 'off' | 'on'
Default: 'on'

This parameter applies only to slow-to-fast transitions. It specifies the initial output of the Rate Transition block at the beginning of a transition when there is no output from the slow block connected to the input of the Rate Transition block. Simulink does not allow the initial output of this block to be Inf or NaN. The value you specify must be a scalar, or have the same dimensions as the input signal.

Programmatic Use

Block Parameter: InitialCondition
Type: character vector
Values: finite scalar
Default: '0'

Specifies a mode for setting the output port sample time. The options are:

  • Specify — Allows you to use the Output port sample time parameter to specify the output rate to which the Rate Transition block converts its input rate.

  • Inherit — Specifies that the Rate Transition block inherits an output rate from the block to which the output port is connected.

  • Multiple of input port sample time — Allows you to use the Sample time multiple (>0) parameter to specify the Rate Transition block output rate as a multiple of its input rate.

If you select Inherit and all blocks connected to the output port also inherit sample time, the fastest sample time in the model applies.

Programmatic Use

Block Parameter: OutPortSampleTimeOpt
Type: character vector
Values: 'Specify' | 'Inherit' | 'Multiple of input port sample time'
Default: 'Specify'

Enter a value that specifies the output rate to which the block converts its input rate. The default value (-1) specifies that the Rate Transition block inherits the output rate from the block to which the output port is connected. See Specify Sample Time in the Simulink documentation for information on how to specify the output rate.

Dependencies

To enable this parameter, set Output port sample time options to Specify.

Programmatic Use

Block Parameter: OutPortSampleTime
Type: character vector
Values: scalar | vector
Default: '-1'

Enter a positive value that specifies the output rate as a multiple of the input port sample time. The default value (1) specifies that the output rate is the same as the input rate. A value of 0.5 specifies that the output rate is half of the input rate. A value of 2 specifies that the output rate is twice the input rate.

Dependencies

To enable this parameter, set Output port sample time options to Multiple of input port sample time.

Programmatic Use

Block Parameter: OutPortSampleTimeMultiple
Type: character vector
Values: scalar
Default: '1'

Block Characteristics

Data Types

Boolean | bus | double | enumerated | fixed point | integer | single

Direct Feedthrough

yes

Multidimensional Signals

yes

Variable-Size Signals

no

Zero-Crossing Detection

no

Extended Capabilities

Fixed-Point Conversion
Convert floating-point algorithms to fixed point using Fixed-Point Designer™.

Introduced before R2006a