I bought several M789 motherboards for my company to make Linux-based routers. The boards seemed very well suitable for such needs and we previously used similar boards (787cl+ and others, not from PC Chips).
The HUGE problem is that the board does not support Power Loss Restart function. That means that if power goes out, then our routers stop working and never resume, even if the power returns. Our routers are ususally installed in places that are hardly reachable and it takes several hours to bring them back up after the power outage. Power outages are often that long that UPS can't handle it. Nobody cares of it, because the outage usually covers the whole building or district. However when the power returns to the building, people want their Internet back. But the router is down due to no "power loss restart". :(
Previously with 787cl+ motherboard it helped to short-circuit the 14th and the 15th pins of the ATX connector so the PSU stayed on. With M789CLU such a trick does not work. The PSU stays on, but the MB doesn't boot.
Does anybody know how can I make the board to be always on? Is there any port register that I should write to? Or is it a CMOS bit?
The board is built around VIA CLE266/VIA8235 chipset.
Thanks in advance for any hints. Alexander Amelkin, MSCS Head of hardware design dept. TRC FIORD, JSC
Previously with 787cl+ motherboard it helped to short-circuit the 14th and the 15th pins of the ATX connector so the PSU stayed on. With M789CLU such a trick does not work. The PSU stays on, but the MB doesn't boot.
Does anybody know how can I make the board to be always on? Is there any port register that I should write to? Or is it a CMOS bit?
Not sure if there's a software solution, but the hardware solution I'd recommend would be a 555 timer or some such. Connect the output to a transistor that would short the power switch lines, and have it pulse every 30sec or so. (29sec off, 1sec on, or thereabouts) That would give the board enough time to get into protected mode (and hence refuse to power down at a single toggle of the switch), while still having a vaguely responsive system after poweron. You would have to disable acpid in Linux to keep it from powering itself down again, but that is not a big deal.
My schematic would look something like this:
^ +5V | +v^v+v^v+-----------+---|(---Ground | | | | +--O---O---O---O--+ | | + DSC THR BYP | | ) 555 | | | GND TRG OUT RST | | +--O---O---O---O--+ | | | | | GND +---)-----------+ | > < > SW+ ----\ | |-+ (NPN) SW- ----/
joshua
Message not GPG signed because it would screw with the ASCII art; sorry. If you would like me to resend with a GPG signature I would be more than happy to do so.
Hi all!
I think, this can be put onto the FAQ.
I found the solution that works for M789 and is very easy and cheap. It also must be a universal solution, helping to power-up any ATX motherboard on power up of the PSU.
Just take a small capacitor (i used a 2uF one) and put it in parallel with the standard power button on your case. Or just connect the capacitor to the PWR BTN header on the motherboard.
This is much easier and cheaper than using any digital solution (with a counter IC or anything). The principle behind my solution is that upon powering up the PSU, the 5VSB line becomes high on the motherboard. That line powers the circuitry needed to react to the power button. Additionally, voltage appears on one of the pins of the PWR BTN header on the mobo (the other pin is ground). So, when there is a capacitor between the pins, it starts charging. That looks like a short circuit to the mobo. It boots up. The capacitor becomes fully charged and it starts looking like an open circuit to the motherboard. The capacitor is never discharged while the mobo is powered and is discharged quickly after the power is removed. Additionally, the functionality of the power button is preserved - you can still push it to turn the PC off.
In other words, the capacitor is equal to "AC Power Loss restart: Always On" setting in the BIOS.
WBR, Alexander mailto:spirit@reactor.ru
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Alexander Amelkin -
Joshua Wise