Preventive techniques

AN1015

10/19

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byte is encountered. In this case, use the techniques described above (for critical bytes) to

remove illegal bytes from your code.

2.6

Averaging the A/D converter results

If you are performing A/D conversion, you can repeat conversions several times, store the

results in the RAM and then average them (or select the most frequently occurring values)

to obtain accurate results in spite of any potential noise errors.

2.7

Register reprogramming and regular checking

It rarely happens that EMC disturbances alter the content of the registers. Generally the

registers concerned are clock control registers or I/O configuration and data registers

because they are close to the chip output pads.

In such cases a good security measure is to refresh these registers frequently.

Table 1. Summary of preventive techniques

Software Quality

Preventive techniques

Advantage

Disadvantage

Implementation

Watchdog

(Hardware or Software)

Control is CPU-

independent

Avoids MCU lock

Needs to be carefully

handled if LP mode is

used

Easy but the activation

and refresh instructions

must be carefully

placed in the code for

maximum efficiency

Force a watchdog reset

in unused program

memory

More direct and quicker

than waiting for a

watchdog timeout

Loss of previous

context

Clear the WDG reset bit

(see device spec.)

Fill unused program

memory with software

interrupt instructions

More direct and quicker

than waiting for a WDG

timeout.

None

Fill unused area with

"TRAP" or SVC



op-code and manage

the failure in the

corresponding interrupt

routine.

A/D Converter

averaging

Ensure the ADC

performance in a noisy

surrounding.

Processing time

Perform an iterative

loop for ADC

acquisitions and

averaging.

Removal of illegal or

critical opcode

Avoid MCU locks due to

unexpected readings of

WFET or WFI opcodes

None, except

restriction on using

these opcodes

String search in the

".list" file (see

Section 2.5).

Input filtering

Data acquisition

stability

Processing time

Repeat measurement

several times and

perform a statistical

choice between "0" or

"1".