Delay power off

July 27, 2008

Hi,

I'm currently working on a project with some specific storage which

internally does a lot of write buffering. The whole thing is working

perfect except of a single problem: when shutting down/suspending/hibernating/

rebooting or whatever the power is cut too fast and the storage

(it is USB bus powered) is not able to complete the cached pending writes

thus we are loosing/corrupting data. Is there any way to delay the

power off. I mean, can I insert an artificial delay after the system

completed the disk I/O (i.e. closed files, flushed registry hives etc)

but before the power is turned off. It is a dirty solution, I know,

and therefore our Linux colleagues had no problem to workaround the

problem this way. Can we do the same on windows? The project is multi-

platform and we need to support at least XP, 2K3 and Vista.

Perhaps some customized shutdown script, a simple kernel mode driver

blocking power IOCTL, anything else. Any ideas are most welcome.

Thank you!

July 28, 2008

Re: Delay power off

voidcoder wrote:

> Hi,

>

> I'm currently working on a project with some specific storage which

> internally does a lot of write buffering. The whole thing is working

> perfect except of a single problem: when shutting

> down/suspending/hibernating/

> rebooting or whatever the power is cut too fast and the storage

> (it is USB bus powered) is not able to complete the cached pending writes

> thus we are loosing/corrupting data. Is there any way to delay the

> power off. I mean, can I insert an artificial delay after the system

> completed the disk I/O (i.e. closed files, flushed registry hives etc)

> but before the power is turned off. It is a dirty solution, I know,

> and therefore our Linux colleagues had no problem to workaround the

> problem this way. Can we do the same on windows? The project is multi-

> platform and we need to support at least XP, 2K3 and Vista.

>

> Perhaps some customized shutdown script, a simple kernel mode driver

> blocking power IOCTL, anything else. Any ideas are most welcome.

>

> Thank you!

>

There are a couple ways you can address this.

1) Understand how it is supposed to work. For example, with a

USB protocol analyser, see what command Windows is sending

to the device, as part of flushing the device cache, before

shutdown. Then, study the command itself. Is the command synchronous

or asynchronous ? Does the command to flush, require an

acknowledgement that flushing is complete, or instead, is the

status from the device ignored, and assumed to be completed ?

You should understand the mechanics, before using a

sledgehammer to fix it.

2) Based on the results of your studies of (1), then

you can look for a workaround, of which there are a few.

Holding up Windows shutdown might work, if the interval is not

too long - there might be timers used in the shutdown sequence,

that will prevent your method from working if you are looking

for extremely long intervals. (Windows might assume the driver

has stopped responding, and kill it anyway.)

USB device ports have a couple options for internal computer

power. Either +5V or +5VSB can be used. +5VSB sticks around,

until you flip off the switch on the back of the computer.

Older motherboards sometimes had a header and a jumper plug,

to set the voltage source (provided for things like waking a

computer by pressing a key on a USB keyboard). Some recent

motherboards, have +5VSB as the only source. The only limitation

of the +5VSB thing, is if you have so many USB devices connected,

that the power supply doesn't have enough current for them all.

If the USB port was +5VSB powered, then you should have time

to finish flushing.

The next level of fix, would be an act of desperation. It is

possible, if your product provided a 20 pin to 20 pin power

cable extension, for your product to fool around with the

PS_ON# signal going to the power supply. You could artificially

keep the power supply running longer than normal, by altering

the protocol to the power supply. PS_ON# is open collector, and

by having a third party device ground PS_ON# for 30 seconds,

that would keep the power supply running for 30 seconds, giving

time for your device to complete its operation. But if anyone

sees such a solution used, naturally they would scoff at it :-)

Another act of desperation, is a power storage device inside

the USB storage thing. There are things like "supercaps", which

can store charge for a number of seconds. These are not

rechargeable batteries, but are capacitors with fairly large

farad ratings. There are rules to their usage, and I'd have

to go back and look that stuff up - there are probably some

rules about rates of current flow and the like. By storing

enough power, for any possible flushing operation, then it

would not matter how curt the OS was.

If you think about it, it would make sense that the issue had

been considered, when the OS was designed. And that spec wise,

there is a mismatch of expectations. I understand, that one

workaround applied at one time, was for Microsoft to delay

shutdown for a couple seconds, to fix a problem like this.

Whether that is an admission that the problem is an OS one,

or was done to help some hardware implementations that are

less than perfect, is something you could research.

Paul

July 28, 2008

Re: Delay power off

"voidcoder" <voidcoder@yahoo.com> wrote in message

news:#hBsssC8IHA.5596@TK2MSFTNGP02.phx.gbl...

> Hi,

>

> I'm currently working on a project with some specific storage which

> internally does a lot of write buffering. The whole thing is working

> perfect except of a single problem: when shutting

down/suspending/hibernating/