79 lines
2.4 KiB
Markdown
79 lines
2.4 KiB
Markdown
Helios64 automatic power on circuitry when main power applied to the system so user does not need to press power button.
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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.
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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.
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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.
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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.
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| State | D | Clock |
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|---------|-------|-------------|
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| Enable | 1 | Rising edge |
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| Disable | 0 | Rising edge |
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## Auto Power On Control under Linux
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*AUTO_ON_EN_D* pin and *AUTO_ON_EN_CLK* pin is assigned to gpio **153** and gpio **154** respectively.
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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.
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To enable the Auto Power On
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```
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echo 1 > /sys/class/gpio/gpio153/value
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echo 0 > /sys/class/gpio/gpio154/value
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sleep 0.1
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echo 1 > /sys/class/gpio/gpio154/value
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sleep 0.1
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echo 0 > /sys/class/gpio/gpio154/value
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```
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To disable the Auto Power On
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```
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echo 0 > /sys/class/gpio/gpio153/value
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echo 0 > /sys/class/gpio/gpio154/value
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sleep 0.1
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echo 1 > /sys/class/gpio/gpio154/value
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sleep 0.1
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echo 0 > /sys/class/gpio/gpio154/value
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```
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## Systemd-shutdown Script
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We put a script to disable Auto Power On during shutdown, located on
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`/lib/systemd/system-shutdown/disable_auto_poweron`.
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The script content:
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```bash
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#!/bin/bash
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# Export GPIO
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# AUTO_ON_D
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echo 153 > /sys/class/gpio/export
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# AUTO_EN_CLK
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echo 154 > /sys/class/gpio/export
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echo out > /sys/class/gpio/gpio153/direction
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echo out > /sys/class/gpio/gpio154/direction
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# Toggling the D Flip-Flop
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echo 0 > /sys/class/gpio/gpio153/value
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echo 0 > /sys/class/gpio/gpio154/value
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sleep 0.1
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echo 1 > /sys/class/gpio/gpio154/value
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sleep 0.1
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echo 0 > /sys/class/gpio/gpio154/value
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```
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!!! Info
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Current implementation does not check whether there is loss of power event.
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