AN725
Rev. 0.1
15
5.2.5. Configuring a Device for Power Mode 3 Fast Wake
In PM3 Fast Wake, all clocks are stopped except for a very low frequency clock (RTC0OSC or LFOSC0) that
allows the core to wake up faster than standard PM3.
To configure a device to run in PM3 Fast Wake:
1. Enable the clocks to peripherals that will be configured by firmware.
2. Select the desired adaptive voltage scaling settings using the LDO module.
3. Disable Power Mode 8 mode in the Clock Control module.
4. Set the AHB clock to the low power oscillator (LPOSC0).
5. Select the fast wake clock source using the PM3CSEL field in the CLKCTRL PM3CN register.
6. Enable fast wake mode by setting the PM3CEN bit to 1 in the PM3CN register.
7. (Optional) Disable the retention mode of any enabled RAM banks.
8. Set the pins in the lowest power configuration for this mode.
9. Set up the desired PMU wakeup source.
10. Put all of the LDOs in low bias mode.
11. Clear the PMU wakeup flags.
12. Disable the SysTick timer.
13. Disable all unused peripherals.
14. Disable the clocks to all unused peripherals.
15. Execute the DSB, ISB, and WFI or WFE instructions. For SiM3L1xx devices, WFI and WFE have the
same behavior.
To measure the data sheet numbers using an SiM3L1xx MCU Card and the AN725_PowerMode3_Fast_Wake
example:
1. Configure the SiM3L1xx MCU Card according to the instructions in “5.2.1. Hardware Setup”.
2. Open the AN725_PowerMode3_Fast_Wake example in either Keil µVision or the Precision32 IDE.
3. Select the desired AHB clock rate using the #defines at the top of the file.
4. Compile and download the code to the device.
5. Disconnect the USB Debug Adapter.
6. Connect PB0.2 to PB1.5 using a short wire and the J21 and J22 headers.
7. Reset the device.
8. Press PB1.7 to place the device in PM3FW. The PB1.5 LED will turn off.
9. Measure the power consumption of the device.
10. Press PB1.5 to wake the device from PM3FW. When this happens, the PB1.7 LED will turn on and the
core will sit in an infinite while(1) loop.
