AN3077 datasheet(42/82 Pages) STMICROELECTRONICS

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Functional safety requirements for application software

AN3077

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DocID16384 Rev 10

ADC_SWTEST_VALCHK The goal of this software test is to verify correct operation of

the control and queue logic of the ADC, and also the CTU, if used. This software

measures implementation is dependant on the ADC configuration (for example, CTU or

CPU mode):

When the ADC is used in CPU mode, the acquired value is read by the ADC_CDRn.

This register includes ADC_CDRn[VALID] and ADC_CDRn[RESULT] fields as well as

channel n converted data (ADC_CDRn[CDATA]). These fields provide status

information about the data acquisition. Application software shall read and verify these

fields after every acquisition.

When the ADC conversion is triggered by the CTU, the acquired digital sample data

are stored in a dual queue along with information about the channel that performed the

acquisition. Checking the channel information of the acquisition provides sufficient

coverage of the control logic and, in part, the queue logic.

Note:

Implementation hint: If ADC is configured to work in CTU mode, the conversion results are

stored in CTU FIFOs (See “Cross-Triggering Unit (CTU)” chapter in Device_Number

Reference Manual). Along with the converted data, the converted channel number and ADC

module are stored. CTU includes two sets of registers to read this information (FIFO Right

aligned data, CTU_FRx, and FIFO Left aligned data, CTU_FLx). User must read these

registers to verify if the sequence of the acquired channel is what is expected.

●

ADC_SWTEST_OVERSAMPLING

In case of Single Read Analog Inputs the

ADC_SWTEST_ADCOVERSAMPLING_CMP must be implemented as counter

measure against random fault.

ADC_SWTEST_OVERSAMPLING is an acquisition redundant in time.

It refers to sampling the signal at rate significantly higher than the Nyquist Frequency

related to the input signal. In case of fault the acquired values are not correlated with

themselves.

This SIF compares the acquired value to verify the correlation.

Against random fault, three consecutive analog values are converted for each

acquisition to implement the ADC_SWTEST_OVERSAMPLING The second

acquisition, A2, is faulty because the first converted value is quite different respect the

other two (See Figure 13).

Figure 13. Series of acquired analog values

Faulty Acquisition

AN3077 Datasheet(PDF) 42 Page - STMicroelectronics