Identify the Root Cause
- Examine the schematic of your device to understand how each component is powered. Know which components need to be powered down in a sequence.
- Review the existing firmware documentation or source code to identify where the improper power-down sequence might be starting.
- Check for power source priority and sequencing requirements, especially in mixed-voltage systems.
Protect Critical Operations
- Ensure that all critical data is saved to non-volatile memory before initiating a power-down. Implement checks to verify the data integrity.
- Implement interrupt service routines to detect imminent power failures or interruptions.
- Add code to handle ongoing data transactions gracefully, making sure these are terminated or completed safely.
Configure GPIOs for Safe States
- Set all GPIO pins to a safe state (e.g., high impedance) for power-down. This prevents any components from being powered on unexpectedly during the shutdown.
- In the code, modify the GPIO configuration as follows:
// Example code to set GPIO pins
void configure_GPIO_for_shutdown() {
// Set all configured outputs to high-impedance mode
pinMode(GPIO_PIN, INPUT); // Assuming a pinMode function that configures pin settings
}
Implement Sequential Shutdown
- Power down components in a specific order to follow the sequence in which power failure would not cause harm to the system.
- Create a shutdown process in the code:
// Example sequential shutdown process
void shutdown_sequence() {
// Call power-off functions for each component in the required order
turn_off_peripheral1();
turn_off_peripheral2();
save_critical_data();
}
// Functions to turn off peripherals
void turn_off_peripheral1() {
// Add specific commands to power off peripheral
}
void turn_off_peripheral2() {
// Add specific commands to power off peripheral
}
Test the Shutdown Process
- Simulate power-down sequences during testing to ensure that all components power down correctly and data is not lost.
- Use an oscilloscope or logic analyzer to verify the power-down sequence timing relative to the application requirements.
- Monitor the system behavior during unexpected shutdowns, verifying that it doesn’t lead to corruption or inconsistency at the firmware level.
Implement Watchdog Mechanisms
- Set up a watchdog timer that can reset the system if the shutdown process fails or stalls beyond an acceptable time frame.
- Implement the watchdog logic in the code:
// Watchdog timer implementation example
void initialize_watchdog() {
// Device-specific watchdog initialization
}
void reset_watchdog() {
// Reset watchdog to maintain system integrity
}
Document the Changes
- Document the new power-down sequence in the firmware’s code comments and project documentation so that future developers understand the design.
- Include information on why specific sequence decisions were made, especially if they impact system performance or power integrity.
