Auto-recovery techniques

AN1015

12/19

DocID5833 Rev 2

3

Auto-recovery techniques

This section gives some techniques for quickly recovering your application context after an

EMC failure.

Unexpected resets, Program Counter jumps and parasitic interrupts are the most common

EMC failures observed in the MCU whatever the source of the disturbance.

In any of these cases the RAM (or EEPROM data memory when available) remains

unchanged and can be used as very efficient way to save the application context and

parameters.

Note that the RAM will lose its contents if the device is powered-off. The EEPROM data

keeps its content at power-off but the write time is much longer.

3.1

Saving your context in RAM

Figure 3 shows an example of a software auto-recovery implementation: the critical

software sequences (door OPEN or CLOSE commands, high speed motor controls) are

memorized in a RAM byte ("RAM(SEQ)").

This allows us on the one hand to recover the context if an EMC event leads to an MCU

reset, and on the other hand we can check the source before a executing a critical

subroutine. In this case the high speed motor activation is allowed only if RAM(SEQ)=03).

The application parameters (T1&T2 timing values) are also stored in RAM when they are

changed.

This means if a software runaway event occurred or the MCU is reset (by the LVD or the

watchdog), the recovery routine (CRR) will restore the last door command, reload the timing

parameters and resume the program execution without any external intervention.