Documentation

Math Operations

hisl_0001: Usage of Abs block

ID: Title	hisl_0001: Usage of Abs block
Description	To support robustness of generated code, when using the Abs block,
	A	Avoid Boolean and unsigned data types as inputs to the Abs block.
	B	Select block parameter Saturate on integer overflow.
Notes	The Abs block does not support Boolean data types. Specifying an unsigned input data type, might optimize the Abs block out of the generated code, resulting in a block you cannot trace to the generated code. For signed data types, Simulink^® does not represent the absolute value of the most negative value. When you select Saturate on integer overflow, the absolute value of the data type saturates to the most positive representable value. When you clear Saturate on integer overflow, absolute value calculations in the simulation and generated code might not be consistent or expected.
Rationale	A	Support generation of traceable code.
Rationale	B	Achieve consistent and expected behavior of model simulation and generated code.
Model Advisor Checks	Check usage of Abs blocks (Simulink Check)
References	IEC 61508-3, Table A.3 (3) 'Language subset' IEC 61508-3, Table A.4 (3) 'Defensive programming' IEC 61508-3, Table A.3 (2) 'Strongly typed programming language’ IEC 61508-3, Table B.8 (3) 'Control Flow Analysis' IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262-6, Table 1 (1b) 'Use of language subsets' ISO 26262-6, Table 1 (1d) 'Use of defensive implementation techniques' ISO 26262-6, Table 7 (1f) 'Control flow analysis' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' EN 50128, Table A.4 (8) 'Strongly Typed Programming Language' EN 50128, Table A.19 (3) 'Control Flow Analysis' DO-331, Section MB.6.3.2.d 'Low-level requirements are verifiable' MISRA C:2012, Dir 4.1
Last Changed	R2018b
Examples	Recommended Not Recommended

hisl_0002: Usage of Math Function blocks (rem and reciprocal)

ID: Title	hisl_0002: Usage of Math Function blocks (rem and reciprocal)
Description	To support robustness of generated code, when using the Math Function block with remainder-after-division (`rem`) or reciprocal (`reciprocal`) functions:
	A	Protect the input of the `reciprocal` function from going to zero.
	B	Protect the second input of the `rem` function from going to zero.
Note	You can get a divide-by-zero operation, resulting in an infinite (`Inf`) output value for the `reciprocal` function, or a Not-a-Number (`NaN`) output value for the `rem` function. To avoid overflows or undefined values, protect the corresponding input from going to zero.
Rationale	Protect against overflows and undefined numerical results.
Model Advisor Checks	Check usage of Math Function blocks (rem and reciprocal functions) (Simulink Check)
References	IEC 61508-3, Table A.3 (3) 'Language subset’ IEC 61508-3, Table A.4 (3) 'Defensive programming’ IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262-6, Table 1(b) 'Use of language subsets' ISO 26262-6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1
Last Changed	R2017b
Examples	In the following example, when the input signal oscillates around zero, the output exhibits a large change in value. You need further protection against the large change in value.

hisl_0003: Usage of Square Root blocks

ID: Title	hisl_0003: Usage of Square Root blocks
Description	To support robustness of generated code, when using the Square Root block, do one of the following:
	A	Account for complex numbers as the output.
	B	Protect the input from going negative.
Rationale	A, B	Avoid undesirable results in generated code.
Model Advisor Checks	Check usage of Sqrt blocks (Simulink Check)
References	IEC 61508-3, Table A.3 (3) 'Language subset’ IEC 61508-3, Table A.4 (3) 'Defensive programming’ IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262-6, Table 1(b) 'Use of language subsets' ISO 26262-6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1
Last Changed	R2016a
Examples

hisl_0028: Usage of Reciprocal Square Root blocks

ID: Title	hisl_0028: Usage of Reciprocal Square Root blocks
Description	To support robustness of generated code, when using the Reciprocal Square Root block, do one of the following:
	A	Protect the input from going negative.
	B	Protect the input from going to zero.
Note	You can get a divide-by-zero operation, resulting in an `(Inf)` output value for the reciprocal function. To avoid overflows or undefined values, protect the corresponding input from going to zero.
Rationale	A, B	Avoid undesirable results in generated code.
Model Advisor Checks	Check usage of Reciprocal Sqrt blocks (Simulink Check)
References	IEC 61508-3, Table A.3 (3) 'Language subset’ IEC 61508-3, Table A.4 (3) 'Defensive programming’ IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262-6, Table 1(b) 'Use of language subsets' ISO 26262-6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1
Last Changed	R2016a
Examples

hisl_0004: Usage of Math Function blocks (natural logarithm and base 10 logarithm)

ID: Title	hisl_0004: Usage of Math Function blocks (natural logarithm and base 10 logarithm)
Description	To support robustness of generated code, when using the Math Function block with natural logarithm (`log`) or base 10 logarithm (`log10`) function parameters,
	A	Protect the input from going negative.
	B	Protect the input from equaling zero.
	C	Account for complex numbers as the output value.
Notes	If you set the output data type to complex, the natural logarithm and base 10 logarithm functions output complex values for negative input values. If you set the output data type to real, the functions output `NAN` for negative numbers, and minus infinity (`-inf`) for zero values.
Rationale	A, B, C	Support generation of robust code.
Model Advisor Checks	Check usage of Math Function blocks (log and log10 functions) (Simulink Check)
References	IEC 61508-3, Table A.3 (3) 'Language subset’ IEC 61508-3, Table A.4 (3) 'Defensive programming’ IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262-6, Table 1(b) 'Use of language subsets' ISO 26262-6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1
Last Changed	R2017b
Examples	You can protect against: Negative numbers using an Abs block. Zero values using a combination of the MinMax block and a Constant block, with Constant value set to `eps` (epsilon). The following example displays the resulting output for input values ranging from `-100` to `100`.

hisl_0005: Usage of Product blocks

ID: Title	hisl_0005: Usage of Product blocks
Description	To support robustness of generated code, when using the Product block with divisor inputs,
	A	In `Element-wise(.*)` mode, protect divisor inputs from going to zero.
	B	In `Matrix(*)` mode, protect divisor inputs from becoming singular input matrices.
Notes	When using Product blocks for element-wise divisions, you might get a divide by zero, resulting in a `NaN` output. To avoid overflows, protect divisor inputs from going to zero. When using Product blocks to compute the inverse of a matrix, or a matrix division, you might get a divide by a singular matrix. This division results in a `NaN` output. To avoid overflows, protect divisor inputs from becoming singular input matrices.
Rationale	A and B	Protect against overflows.
Model Advisor Checks	Adherence to this modeling guideline cannot be verified by using a Model Advisor check.
References	IEC 61508-3, Table A.3 (3) 'Language subset’ IEC 61508-3, Table A.4 (3) 'Defensive programming’ IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262-6, Table 1 (1b) 'Use of language subsets' ISO 26262-6, Table 1 (1d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.4.2.2 'Robustness Test Cases’ DO-331, Section MB.6.4.3 'Requirements-Based Testing Methods’ DO-331, Section MB.6.3.1.e 'High-level requirements conform to standards' DO-331, Section MB.6.3.2.e 'Low-level requirements conform to standards' DO-331, Section MB.6.3.1.g 'Algorithms are accurate' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' DO-331, Section MB.6.3.3.b 'Software architecture is consistent' MISRA C:2012, Dir 4.1
Prerequisites	hisl_0314: Configuration Parameters > Diagnostics > Data Validity > Signals
Last Changed	R2019a

hisl_0029: Usage of Assignment blocks

ID: Title	hisl_0029: Usage of Assignment blocks
Description	To support robustness of generated code, when using the Assignment block, initialize array fields before their first use.
Notes	If the output vector of the Assignment block is not initialized with an input to the block, elements of the vector might not be initialized in the generated code. When the Assignment block is used iteratively and all array field are assigned during one simulation time step, you do not need initialization input to the block. Accessing uninitialized elements of block output can result in unexpected behavior.
Rationale	Avoid undesirable results in generated code.
Model Advisor Checks	Check usage of Assignment blocks (Simulink Check)
References	IEC 61508-3, Table A.3 (3) 'Language subset’ IEC 61508-3, Table A.4 (3) 'Defensive programming’ IEC 61508-3, Table A.3 (2) ‘Strongly typed programming language’ IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262–6, Table 1(b) 'Use of language subsets' ISO 26262–6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' EN 50128, Table A.4 (8) 'Strongly Typed Programming Language' DO-331, Section MB.6.3.1.e 'High-level requirements conform to standards’ DO-331, Section MB.6.3.2.e 'Low-level requirements conform to standards’ MISRA C:2012, Rule 9.1
Last Changed	R2016a
Examples	Not Recommended: No initialization input Y0 when block is not used iteratively Recommended: Initialization input Y0 when block is not used iteratively Recommended: Initialize array fields when block is used iteratively

hisl_0066: Usage of Gain blocks

ID: Title	hisl_0066: Usage of Gain blocks
Description	To support traceability of generated code, the value of the Gain block must not resolve to `1`.
Notes	The code generation process can remove Gain values equal to `1` during optimization, resulting in model elements with no traceable code. An exception to this rule is setting the Gain value to a named parameter data object with a non-auto storage class.
Rationale	Support the generation of traceable code.
Model Advisor Checks	Check usage of Gain blocks (Simulink Check)
References	DO-331, Section MB.6.3.2.d 'Low-level requirements are verifiable' IEC 61508-3, Table A.3 (3) 'Language subset' IEC 61508-3, Table A.4 (3) 'Defensive programming' IEC 61508-3, Table B.8 (3) 'Control Flow Analysis' IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262-6, Table 1 (1b) 'Use of language subsets' ISO 26262-6, Table 1 (1d) 'Use of defensive implementation techniques' ISO 26262-6, Table 7 (1f) 'Control flow analysis' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' EN 50128, Table A.19 (3) 'Control Flow Analysis'
Last Changed	R2018a

Simulink Documentation

Support