Sqrt

Implement control-signal-based square root function

Since R2020b

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Description

The Sqrt block performs the square root operation of the input data signal. The block has control signals that indicate whether the input and output data are valid. You can also specify the number of iterations of the algorithm and the latency strategy.

To use this block in your Simulink^® model, open the HDLMathLib library by entering this command in the MATLAB^® Command Window:

open_system("HDLMathLib")

Latency Considerations

You can simulate the Sqrt block with latency. This block is a masked subsystem that contains the LumpLatency MATLAB Function block. The subsystem uses this MATLAB Function block to compute the latency based on the input and output data types. The software calculates the latency of the block using the word length and fractional length of fixed-point input and output.

The block supports three latency modes. You can specify a custom latency value by setting the Latency Strategy parameter to Custom.

To view the function that computes the latency of the block, open the LumpLatency block in the masked subsystem. To view inside the mask, click the ⇩ icon on the block. For more information, see Lump Latency for Square-root Block.

Examples

Implement Sqrt Block with Control Signals

Implement the control-signal based Square root block and use it to generate HDL code.

• Open Script

Limitations

The block has these limitations:

• Does not support floating-point data types, such as half, single, and double.

• Cannot be used in Synchronous Subsystem.

• Does not support resource sharing optimization.

Ports

Input

dataIn — Input data signal

scalar | vector

Input signal to calculate the square root.

Data Types: int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | bus

validIn — Indication of whether input control signal is valid

scalar

Input control signal that indicates whether the input signal is valid.

Data Types: Boolean

Output

dataOut — Output data signal

scalar | vector

Output signal that is the square root of the input signal.

Data Types: int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | bus

validOut — Indication of whether output control signal is valid

scalar

Output control signal that indicates whether output signal is valid.

Data Types: Boolean

Parameters

Latency strategy — Latency strategy

Max (default) | Min | Custom | Zero

Specify whether to map the blocks in your design to minimum, maximum, custom, or zero latency. For more information, see LatencyStrategy.

Programmatic Use

Block Parameter: latencyMode

Type: character vector

Values: 'Max' | 'Min' | 'Custom' | 'Zero'

Default: 'Max'

Custom latency — Custom latency value

0 (default)

When you set Latency strategy to Custom, use this parameter to specify the custom latency value. The latency must be a nonnegative integer in the range [0, L], where L is the maximum latency value of Sqrt block. For more information, see CustomLatency.

Dependency

To use this parameter, set Latency strategy to Custom.

Programmatic Use

Block Parameter: customLatencyValue

Type: Integer

Values: 0 to Max latency

Default: 0

Output data type — Output data type

Inherit: Same as first input (default) | Inherit: Inherit via internal rule | Inherit: Inherit via back propagation | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16,0) | <data type expression>

Specify the output data type. The data type can be inherited or specified directly.

Programmatic Use

Block Parameter: OutDataTypeStr

Type: character vector

Values: 'Inherit: Inherit via internal rule' | 'Inherit: Inherit via back propagation' | 'Inherit: Same as first input' | 'int8' | 'uint8' | int16 | 'uint16' | 'int32' | 'uint32' | 'int64' | 'uint64' | fixdt(1,16,0) | '<data type expression>'

Default: 'Inherit: Same as first input'

Saturate on integer overflow — Option to choose behavior when integer overflow occurs

off (default) | on

Action	Reasons for Taking This Action	What Happens for Overflows	Example
Select this check box.	Your model has possible overflow, and you want explicit saturation protection in the generated code.	Overflows saturate to either the minimum or maximum value that the data type can represent.	The maximum value that the int8 (signed, 8-bit integer) data type can represent is 127. Any block operation result greater than this maximum value causes overflow of the 8-bit integer. With the check box selected, the block output saturates at 127. Similarly, the block output saturates at a minimum output value of -128.
Do not select this check box.	You want to optimize efficiency of your generated code. You want to avoid overspecifying how a block handles out-of-range signals. For more information, see Troubleshoot Signal Range Errors.	Overflows wrap to the value that is representable by the data type.	The maximum value that the int8 (signed, 8-bit integer) data type can represent is 127. Any block operation result greater than this maximum value causes overflow of the 8-bit integer. With the check box cleared, the software interprets the overflow-causing value as int8, which can produce an unintended result. For example, a block result of 130 (binary 1000 0010) expressed as int8, is -126.

When you select this check box, saturation applies to every internal operation on the block, not just the output or result. Usually, the code generation process can detect when overflow is not possible. In this case, the code generator does not produce saturation code.

Programmatic Use

Block Parameter: SaturateOnIntegerOverflow

Type: character vector

Value: 'off' | 'on'

Default: 'off'

Integer rounding mode — Rounding mode for fixed-point operations

Zero (default) | Ceiling | Floor | Nearest | Simplest

Specify the rounding mode for fixed-point operations. For more information, see Rounding Modes.

Programmatic Use

Block Parameter: RndMeth

Type: character vector

Values: 'Zero' | 'Ceiling' | 'Floor' | 'Nearest' | 'Simplest'

Default: 'Zero'

Tips

The block supports HDL code generation using HDL Coder™. HDL Coder supports additional configuration options that affect HDL implementation and synthesized logic. For more information, see HDL Block Properties.

Algorithms

Lump Latency for Square-root Block

The software uses the LumpLatency MATLAB Function block to compute the latency of the square root operation. The block has four latency modes: Min, Max, Custom, and Zero. For more information, see LatencyStrategy and CustomLatency.

Latency Strategy	Latency Value
Max	The software calculates the latency L by using this equation: L = K + 2, where K depends on the fixed-point input and output data type.
Min	The software calculates the latency L by using this equation: L = floor( (K + 2) / 2), where K depends on the fixed-point input and output data type.
Custom	Specify the latency value for the block by entering the value between zero and maximum latency in the Custom latency parameter.
Zero	The latency of the block is 0.

The software calculates the value of K using the word length and fractional length of the fixed point input and output.

• For fixed-point signed output:

  K = min((OutputWL - 1), (OutputIL + OutputFL) ).

• For fixed-point unsigned output:

  K = min((OutputWL), (OutputIL + OutputFL) ),

where OutputWL is an output word length, OutputFL is an output fractional length, and OutputIL is an output integer length given by:

OutputIL = ceil((InputWL - InputFL) / 2),

where InputWL is an input word length and InputFL is an input fractional-length.

To view the LumpLatency block, click the ⇩ icon on the block.

Version History

Introduced in R2020b