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 2008-2012 Microchip Technology Inc. DS01229C-page 1

AN1229

INTRODUCTION

This application note describes the Class B Safety

Software Library routines that detect the occurrence of

Faults in a single channel CPU. These routines have

been developed in accordance with the IEC 60730

standard to support the Class B certification process.

These routines can be directly integrated with the end

user’s application to test and verify the critical

functionalities of a controller without affecting the end

user’s application.

This application note also describes the Application

Programming Interface (API) functions that are

available in the Class B Safety Software Library.

The Class B safety software routines can be called

periodically at start-up or run time to test the following

components:

• CPU Registers

• CPU Program Counter

• Invariable Memory

• Variable Memory

• Clock

• Interrupt Handling and Execution

This application note also outlines various techniques,

which are not part of the Class B Safety Software

Library, to test components such as external communi-

cation, timing, I/O periphery, analog I/O and analog

multiplexer.

OVERVIEW OF THE IEC 60730

STANDARD

The IEC 60730 standard defines the test and diagnostic

methods that ensure the safe operation of the controlled

equipment used in household appliances. Annex H of

the IEC 60730 standard classifies the software into the

following categories (see Appendix B: “IEC 60730-1

Table H.11.12.7”):

• Class A

• Class B

• Class C

The Class B Safety Software Library implements the

important test and diagnostic methods that fall into the

Class B category. These methods use various

measures to detect and respond to the software-

related Faults and errors.

According to the IEC 60730 standard, the controls with

functions that fall into the Class B category should have

one of the following structures:

• Single Channel with Functional Test

In this structure, the Functional test is executed

prior to the application firmware execution.

• Single Channel with Periodic Self-Test

In this structure, the Periodic tests are embedded

within the firmware, and the self-test occurs

periodically while the firmware is in Execution

mode.

• Dual Channel without Comparison

In this structure, two independent methods execute

the specified operations.

Note: The term ‘IEC 60730 standard’ used in

this document refers to the “IEC 60730-1

Switzerland. www.iec.ch.

Authors: Veena Kudva & Adrian Aur

Microchip Technology Inc.

Note: “The author thanks the International Elec-

trotechnical Commission (IEC) for permis-

sion to reproduce information from its

International Standard IEC 60730-1ed.3.2

(2007). All such extracts are copyright of

IEC, Geneva, Switzerland. All rights

reserved. Further information on the IEC is

available from www.iec.ch. IEC has no

responsibility for the placement and con-

text in which the extracts and contents are

reproduced by the author, nor is IEC in any

way responsible for the other content or

accuracy therein.”

Class B Safety Software Library for

PIC® MCUs and dsPIC® DSCs

AN1229

DS01229C-page 2  2008-2012 Microchip Technology Inc.

SYSTEM REQUIREMENTS

The following system requirements are recommended

to run the Class B Safety Software Library:

• For the tests that require the independent time

slot monitoring, the system hardware must be

provided with at least two independent clock

sources (e.g., crystal oscillator and line

frequency).

• The user application determines whether the

interrupts need to be enabled or disabled during

the execution of the Class B Safety Software

Library.

If an interrupt occurs during the execution of the

Class B Safety Software Library routine, an

unexpected change may occur in any of the regis-

ters. Therefore, when the Interrupt Service Routine

(ISR) executes, the contents of the register will not

match the expected content, and the ISR will return

an incorrect result.

CLASS B SAFETY SOFTWARE

LIBRARY

The Class B Safety Software Library, which applies to 8-

bit, 16-bit, and 32-bit devices, includes several APIs,

which are intended to maximize application reliability

through Fault detection. These APIs help meet the IEC

60730 standard compliance. The following tests can be

implemented using this library:

• CPU Register Test

• Program Counter Test

• Variable Memory Test

• Invariable Memory (Flash/EEPROM) Test

• Interrupt Test

• Clock Test

In the following sections, the test description and the

implementation details are discussed for each test. In

addition, each section also lists the APIs that are

required to execute the corresponding test for

supported architectures.

CPU Register Test

The CPU Register test implements the

functional test H.2.16.5 defined by the IEC 60730

standard. It detects stuck-at Faults in the CPU registers.

This ensures that the bits in the registers are not stuck at

a value ‘0’ or ‘1’; this is a non-destructive test.

This test performs the following major tasks:

1. The contents of the CPU registers to be tested

are saved on the stack before executing the

routine.

2. The registers are tested by first successively

writing the binary sequences (length is depen-

dant upon architecture), 010101... followed by

101010... into the registers, and then reading

the values from these registers for verification.

3. The test returns an error code if the returned

values do not match.

API FUNCTIONS

The following API functions implement the CPU

• SSL_8bit_CPU_RegisterTest (PIC10/12/16)

• SSL_8bitsFamily_CPU_RegisterTest (PIC18)

• SSL_16bitsFamily_CPU_RegisterTest

• SSL_32bitsFamily_CPU_RegisterTest

Note: The interrupts should be disabled during

the execution of the CPU Register test so

that the register integrity is preserved at all

times.

 2008-2012 Microchip Technology Inc. DS01229C-page 3

AN1229

Program Counter Test

The Program Counter (PC) test implements the func-

tional test H.2.16.5 defined by the IEC 60730 standard.

The PC holds the address of the next instruction to be

executed.

The test performs the following major tasks:

1. The PC test invokes the functions that are

located in the Flash memory at different

addresses.

2. These functions return a unique value.

3. The returned value is verified using the PC test

function.

4. If the values match, the PC branches to the

correct location.

The customized linker script defines the addresses

where these functions reside in the Flash memory. The

functions placed at these addresses return a unique

value, which is the starting address of the called func-

tion. Example 1 shows how to modify the linker script to

place a function in the Flash memory. The actual Flash

address space is processor dependent. Please refer to

the processor-specific linker script example provided.

API FUNCTIONS

The following API functions implement the PC test:

• SSL_8bit_PCtest (PIC10/12/16)

• SSL_8bitsFamily_PCtest (PIC18)

• SSL_16bitsFamily_PCtest

•SSL_32bitsFamily_PCtest

EXAMPLE 1: LINKER SCRIPT MODIFICATION

Note 1: The user application defines the address

where the PC branches.

2: The size of the program memory varies

by device. Refer to the specific device

data sheet for more details.

/* The modified linker script */

SslTestSection1 0x900:

{

*(.SslTestSection1);

} program

/* The SSL_TestFunction1 function*/

long __attribute__((__section__(“.SslTestSection1”))) SSL_TestFunction1()

{

return((long)&SSL_TestFunction1);

}

Produktspecifikationer

Varumärke:	Microchip
Kategori:	Inte kategoriserad
Modell:	PIC24FJ128GL405

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