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How to power up when power applied

Former Member

I have an embedded application in mind for the ultra96 board that requires booting automatically when power is first applied.  I believe in the 96boards specification (consumer boards, low cost, rev 1.0 2015 pg. 10) says that that boards should either have a switch that manually control power to them or boot automatically at first application of power if they are using a soft power switch.

I tried to find a way to power up and boot automatically in the user guide and by looking in the schematics but there didn't seem to be a way to do it.

In the schematic there are two 0 ohm resistors on the power_en line going to CTL4 input of the TPS6508641: R161 and R56.  Usually 0 ohms are there for config. purposes.

There's also an I2C interface to the TPS6508641 part.  Does the part have the ability to be configured over the I2C bus through the OS ?

Board power-up/boot when power is first applied is very common and necessary for embedded applications.  Hopefully there's a way to do this on the current boards and if not this feature will be added on the next revision if not.

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    To my knowledge we can't support hard power up without some external modification. The reason is we use a power controller that holds the Zynq in reset during power up and also controls power down to make sure the flash doesn't get corrupted.

    That being said, the power button output is connected to J7 pin 4, which is the larger expansion header on the board. You can't simply hard wire it to GND, which I tried first, because the power controller looks for a falling edge on that input to turn on power. You could wire in an external circuit that grounds that pin after power is applied, but again with the board hardware this isn't supported without some external trickery. The reason for the soft power button on this platform is that we run things from flash (fogive me if I get some of this wrong, I'm the power guy and I'm going by memory of what my colleagues told me). If you remove power without proper shut down you can corrupt the file system. If you decide to try and mock something up using the J7 access, please be mindful of protecting the file system from hard shut down. I hope this is helpful.

    thanks

    Chris

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  • 0

    To my knowledge we can't support hard power up without some external modification. The reason is we use a power controller that holds the Zynq in reset during power up and also controls power down to make sure the flash doesn't get corrupted.

    That being said, the power button output is connected to J7 pin 4, which is the larger expansion header on the board. You can't simply hard wire it to GND, which I tried first, because the power controller looks for a falling edge on that input to turn on power. You could wire in an external circuit that grounds that pin after power is applied, but again with the board hardware this isn't supported without some external trickery. The reason for the soft power button on this platform is that we run things from flash (fogive me if I get some of this wrong, I'm the power guy and I'm going by memory of what my colleagues told me). If you remove power without proper shut down you can corrupt the file system. If you decide to try and mock something up using the J7 access, please be mindful of protecting the file system from hard shut down. I hope this is helpful.

    thanks

    Chris

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  • 0 in reply to ctammann

    I didn't see the powerbutton connection to the J7 pin 4.  Thanks for pointing that out.  I can add a circuit to the carrier card that will toggle that pin after a delay enabling the system to boot at power up.

    The risk of SD card corruption is always possible if the power fails during a write.  In rare cases it can actually brick the card.  Some cards have an internal remap table for wear leveling.  If that table gets corrupted it can take special s/w and even a special programmer to fix the card.  Most cards are designed to finish critical internal writes if a power failure occurs, but some don't.  User data is a different stoy.  It's up to the OS to handle that properly. The embedded OS (LInux) is using Ext4 on the card for the main filesystem.  Ext4 is a journaling filesystem that handles power failures causing partial writes fairly well. 

    Part of doing and embedded design is figuring out how to let the OS know the power is failing and providng it enough time to shut down.  It's why they sell micro UPS units for things like the Raspberry PIs and other embedded systems.

    The 96boards standard requires boards to be able to boot from power applied even if they have soft power buttons.   So you may want to think about enabling this in future versions of this board.  You can still have the soft power down, but you should have a way to enable the board to boot on power application.  

    Thank you again for your comments and pointing out the J7 pin 4.