[Nut-upsuser] [OT?] How often does/should NUT poll an UPS or my PSU?

Michelle Konzack linux4michelle at freenet.de
Tue Mar 18 11:32:43 UTC 2008


Maybe a little bit Off-Topic but:

QUESTION 1: How often does/should NUT poll an UPS or my PSU?

I have this question since I have a hardware design problem.

Hardware Description:
The PSU is modular (all power modules, like "ATX", "P4", "ePCI", "SATA",
"Device" can be choosen as needed) where I have two type of Base Boards:

    1)  Base Board 1
        only OVP/UVP protection and no other electronic (incl. USB)

    2)  Base Board 2
        Microcontroller supported PowerWhatch with USB and NUT support

On "Base Board 2" I have only to whatch the Uin,  Iin  and  temperature,
which mean, I need two A/D-Converter and a temperatur sensor.  The "Base
Board 2" identify it self over the USB  port  by  using  an  I²C  EEPROM
conencted directly to the USB-Host  Controller.  (Tested  and  it  works
with my Evaluation Board from NXP;  I like success :-)

Now I am thinking to add a VERY Low-Cost  USB-Host-Controller  to  "Base
Board 1" to get at least the Uin and use a  simpel  A/D-Converter  which
then can be read over USB from NUT which then can consider to ignore it,
let the computer go into standby or shut the computer down.

QUESTION 2: Should I expose the value of the A/D  Converter  to  the
            USB port which let the ${USER} choose when to  shoutdown
            the computer or should I set fixed values with a Window-
            Discriminator and send only a "Under Voltage" signal?

So, this are not very difficult, since even  a  parallel2usb  controller
does not need a Microcontroller... :-)

The biggest problem are the ATX module where I like  to  get  the  Volt,
Ampere and Temperature like:

    1)  +12  V
    2)  + 5  V
    3)  + 3.3V
    4)  + 5  Vsb
    5)  -12  V
    6)  Temperature

So, this are effectiv 11 values to get on ONLY the ATX module.

On another mailinglist, someone suggest to forget  I²C  and  use  Maxims
1-Wire Technology and do Bit-Banging...  but there is a  timing  problem
with 1-Wire:  16.3 kbit/s

If I go the way with 1-Wire, I would put on the "Base Board 2" a  Micro-
controller which  support  I²C and then put a I²C-Switch  onto  it.  The
first 5 ports would be each connected to one of the 5 Port/Module  Slots
on the "Base Board 2" which is needed to  identify  EACH  slot  and  the
Module inserted.

Then on the Module I put a "Singel  Channel  1-Wire  Master"  DS2482-100
which convert the I²C to 1-Wire...

And now it comes:  To get the 11 values described above, I have the need
for three "Quad A/D Converter" DS2450 (from the third there are only two
used), a "High-Precission 1-Wire  Digital  Thermometer"  DS18S20  and  a
"Silicon Serial Number" DS2401 (customisable) which identify the module.

Now, the 1-Wire protocol say, you have to "scan" the 1-Wire bus to know,
which devices are connected and get its ID and then you have to poll the
devices.  On the ATX module at start-up 5 devices and  then  continously
4 devices.

OK, this is done by the Microcontroller on the "Base  Board  2"  but  it
seems I can not get the whole set of DATA in less then 3 seconds...

Result: NUT can not poll the PSU in less then 4 seconds...

QUESTION 3: Should I realy go the way with Maxims 1-Wire technology?

Now, going back to the website of NXP/Philips looking for I²C  stuff,  I
have found an "Quad A/D Converter" and "EEPROMS"  (maybe  overkill)  but
currently not found a temperatur sensor (it is  desribed  but  have  not
found its part number).

So, I²C would do the stuff in less then 200 milli seconds which mean, it
is at least 15 times faster.

QUESTION 4: It is better to use I²C even if the, e.g. ATX  module,
            would be arround 4 US$ more expensive?

The avantage with I²C is, that I have only ONE protocol and its faster.

Thanks, Greetings and nice Day
    Michelle Konzack
    24V Electronic Engineer
    Tamay Dogan Network
    Debian GNU/Linux Consultant

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