AN3181

Class B solution structure

Doc ID 17286 Rev 2

17/31

4

Class B solution structure

4.1

Integrating software into user application

Class B routines are divided into two main processes: periodic run mode self tests and

startup tests. The periodic run mode test must be initialized by the set-up block before it is

applied. All the blocks are checked by sufficient flow control checked at a number of flow

check points (see Section 3.1.3: Class B flow control). All class B variables are kept

redundantly in a pair of control registers stored in the Class B variable space defined by user

(see Section 3.1.2: Class B variables). This variable space is split into two separate RAM

regions which are permanently undergoing the transparent test as a part of run mode tests.

Figure 4: Integration of startup and periodic run mode self tests into application shows the

basic principle of how to integrate the Class B software package into user software. The

reset vector should be forced by the user to STL_StartUp() routine which collects all system

startup self tests. If they pass successfully, then the standard initialization procedure of

C-compiler routine is performed. While the application is running, periodic tests must be

executed at regular intervals. To ensure this, the user must initialize these tests by calling

the initialization routine STL_InitRunTimeChecks() before entering main loop and then

inserting a periodical call of STL_DoRunTimeChecks() at main level. For best results, this

should be inside the main loop. TIM4 (or TIM6 for some devices), which is configured during

initialization routine to generate periodic system interrupts, provides the time base for all the

tests. Short partial transparent RAM March C- or March X check is performed at each

interrupt tick. If any self test fails, FailSafe() routine is called.

Figure 4.

Integration of startup and periodic run mode self tests into application

4.2

Detailed description of startup self tests

The startup self test is forced during initialization phase as the earliest checking process

after resetting the microcontroller (see Figure 4) and before standard application startup