Add low power example

Author: nseidle

libraries/Examples/examples/Advanced/LowPower/LowPower.ino

@@ -0,0 +1,94 @@
+/*
+  Artemis Low Power: How low can we go?
+  By: Nathan Seidle
+  SparkFun Electronics
+  Date: October 17th, 2019
+  License: This code is public domain. Based on deepsleep.c from Ambiq SDK v2.2.0.
+  A big thanks to robin_hodgson for pointing out the HFRC shutdown requirement.
+
+  SparkFun labored with love to create this code. Feel like supporting open source hardware?
+  Buy a board from SparkFun! https://www.sparkfun.com/products/15376
+
+  How close can we get to 2.7uA in deep sleep?
+  This example shows how decrease the Artemis current consumption to less than 3uA in deep sleep.
+
+  To monitor the current to the Edge cut the MEAS jumper, solder in headers, and attach
+  a DMM via IC hooks (https://www.sparkfun.com/products/506).
+
+  The USB to serial bridge draws some current:
+    Serial Basic C - ~1.2uA (https://www.sparkfun.com/products/15096)
+    FTDI Basic - ~5.5uA (https://www.sparkfun.com/products/9873)
+
+  The various components on the Edge2 can be powered on/off as well
+    PDM microphones (2) - ~50.9uA
+    Accelerometer (POR mode) - ~79.7uA
+    Camera regulator enabled (no camera) - ~96.8uA
+*/
+
+void setup()
+{
+  Serial.begin(115200);
+  Serial.println("Low power sleep example");
+
+#if defined(ARDUINO_SFE_EDGE2)
+  pinMode(ACCEL_VDD, OUTPUT);
+  digitalWrite(ACCEL_VDD, LOW);
+
+  pinMode(MIC_VDD, OUTPUT);
+  digitalWrite(MIC_VDD, LOW);
+
+  pinMode(CAMERA_VDD, OUTPUT);
+  digitalWrite(CAMERA_VDD, LOW);
+#endif
+
+  //Turn off ADC
+  power_adc_disable();
+
+  // Initialize for low power in the power control block
+  am_hal_pwrctrl_low_power_init();
+
+  // Stop the XTAL.
+  am_hal_clkgen_control(AM_HAL_CLKGEN_CONTROL_XTAL_STOP, 0);
+
+  // Disable the RTC.
+  am_hal_rtc_osc_disable();
+
+  // The default Arduino environment runs the System Timer (STIMER) off the 48 MHZ HFRC clock source.
+  // The HFRC appears to take over 60 uA when it is running, so this is a big source of extra
+  // current consumption in deep sleep.
+  // For systems that might want to use the STIMER to generate a periodic wakeup, it needs to be left running.
+  // However, it does not have to run at 48 MHz. If we reconfigure STIMER (system timer) to use the 32768 Hz
+  // XTAL clock source instead the measured deepsleep power drops by about 64 uA.
+  am_hal_stimer_config(AM_HAL_STIMER_CFG_CLEAR | AM_HAL_STIMER_CFG_FREEZE);
+
+  // This option selects 32768 Hz via crystal osc. This appears to cost about 0.1 uA versus selecting "no clock"
+  am_hal_stimer_config(AM_HAL_STIMER_XTAL_32KHZ);
+
+  // This option would be available to systems that don't care about passing time, but might be set
+  // to wake up on a GPIO transition interrupt.
+  // am_hal_stimer_config(AM_HAL_STIMER_NO_CLK);
+
+  // Turn OFF Flash1
+  if (am_hal_pwrctrl_memory_enable(AM_HAL_PWRCTRL_MEM_FLASH_512K))
+  {
+    while (1)
+      ;
+  }
+
+  // Power down SRAM
+  PWRCTRL->MEMPWDINSLEEP_b.SRAMPWDSLP = PWRCTRL_MEMPWDINSLEEP_SRAMPWDSLP_ALLBUTLOWER32K;
+
+  Serial.println("Going to sleep...");
+  delay(100); //Wait for print to complete
+
+  Serial.end(); //Disable Serial
+
+  am_hal_sysctrl_sleep(AM_HAL_SYSCTRL_SLEEP_DEEP);
+
+  //We should never get here.
+}
+
+void loop()
+{
+  //Do nothing
+}