Helios64: Added Auto Power On page

docs/helios64/auto_poweron.md

@@ -0,0 +1,79 @@
+Helios64 automatic power on circuitry when main power applied to the system so user does not need to press power button.
+This is useful in case of loss of main power longer than UPS back up time. The system will automatically power on when main power return.
+
+![!Auto power on State](/helios64/img/auto-poweron/flowchart.png)
+
+U-Boot will enable Auto Power On and a [systemd-shutdown](https://www.freedesktop.org/software/systemd/man/systemd-shutdown.html) hook script to disable the Auto Power On during graceful shutdown.
+
+
+By default the system need the user to press power button to power up. This behaviour can be changed by manipulating a set of GPIOs.
+The circuitry uses [D Flip Flop](https://en.wikipedia.org/wiki/Flip-flop_(electronics)#D_flip-flop) and rely on RTC battery or UPS battery to keep the state.
+
+![!Auto Power On Schematic](/helios64/img/auto-poweron/schematic_flip_flop.png)
+
+|  State  | D     | Clock    |
+|---------|-------|-------------|
+| Enable  | 1     | Rising edge |
+| Disable | 0     | Rising edge |
+
+
+## Auto Power On Control under Linux
+
+*AUTO_ON_EN_D* pin and *AUTO_ON_EN_CLK* pin is assigned to gpio **153** and gpio **154** respectively.
+After exporting and configure the GPIOs as output (refer to [GPIO Control](/helios64/gpio/#gpio-control)), we will do bit-banging to configure the D Flip Flop.
+
+To enable the Auto Power On
+
+```
+echo 1 > /sys/class/gpio/gpio153/value
+echo 0 > /sys/class/gpio/gpio154/value
+sleep 0.1
+echo 1 > /sys/class/gpio/gpio154/value
+sleep 0.1
+echo 0 > /sys/class/gpio/gpio154/value
+```
+
+To disable the Auto Power On
+
+```
+echo 0 > /sys/class/gpio/gpio153/value
+echo 0 > /sys/class/gpio/gpio154/value
+sleep 0.1
+echo 1 > /sys/class/gpio/gpio154/value
+sleep 0.1
+echo 0 > /sys/class/gpio/gpio154/value
+```
+
+## Systemd-shutdown Script
+
+We put a script to disable Auto Power On during shutdown, located on
+
+`/lib/systemd/system-shutdown/disable_auto_poweron`.
+
+The script content:
+
+```bash
+#!/bin/bash
+
+# Export GPIO
+# AUTO_ON_D
+echo 153 > /sys/class/gpio/export
+# AUTO_EN_CLK
+echo 154 > /sys/class/gpio/export
+
+echo out > /sys/class/gpio/gpio153/direction
+echo out > /sys/class/gpio/gpio154/direction
+
+# Toggling the D Flip-Flop
+echo 0 > /sys/class/gpio/gpio153/value
+echo 0 > /sys/class/gpio/gpio154/value
+sleep 0.1
+echo 1 > /sys/class/gpio/gpio154/value
+sleep 0.1
+echo 0 > /sys/class/gpio/gpio154/value
+```
+
+!!! Info
+    Current implementation does not check whether there is loss of power event.
+
+

mkdocs.yml

@@ -82,6 +82,7 @@ nav:
     - First Start : 'helios64/install/first-start.md'
   - Hardware:
     - Overview: 'helios64/hardware.md'
+    - Auto Power On: 'helios64/auto_poweron.md'
     - Button: 'helios64/button.md'
     - Ethernet: 'helios64/ethernet.md'
     - Front Panel: 'helios64/front-panel.md'