Computer power-up problem

IME you do, maybe you get a few seconds grace.

Reply to
Andy Burns
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On 19:28 16 Jan 2019, Andy Burns snipped-for-privacy@andyburns.uk wrote in news: snipped-for-privacy@mid.individual.net:

This PC repair book discusses ways the CMOS retains charge for a short while. The author points out it's almost NV-RAM but does actually need some current.

First 2 or 3 links listed here:

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Reply to
Pamela

By having the bios initially check the status of that jumper and clear the settings in the eeprom.

Reply to
dkol

Its got it because it has just been turned on.

Reply to
dkol

Yes, but as I said before the grace period is pretty short, I've been dealing with PCs since before they even had RTC/CMOS.

Reply to
Andy Burns

Don?t need an auxiliary microprocessor, just have the main cpu check the jumper position or the checksum first thing in the boot sequence.

Reply to
dkol

an experiment:

shutdown pc, unplug from mains, remove battery, short cmos pins, un-short pins, re-insert battery, power back on ...

Reply to
Andy Burns

On 22:42 16 Jan 2019, Andy Burns snipped-for-privacy@andyburns.uk wrote in news: snipped-for-privacy@mid.individual.net:

I guess you didn't follow the link.

Reply to
Pamela

Or just a fake Chinese battery.

Over Xmas we had some of those LED tee lights that run on CR2032 lithium coin batteries.

The LEDs ran continuously for 4 days with a Duracell branded CR2032 battery from a reliable source.

The same LED tee lights ran for less than 6 hours at full brightness then a few hours at a much dimmed brightness with Maxwell branded CR2032 batteries obtained cheaply on Ebay.

Reply to
alan_m

Battery backed RAM was popular when non-volatile memory was one time programmable and hence didn't have the capability to be altered once programmed.

These days EEPROM/flash is common place in computers and TV set top boxes and used where data needs to be non-volatile. It doesn't need battery or power to maintain the data. They can be re-programmed and often have a section that can be effectively protected so it cannot be overwritten. This protected section is usually used for a factory installed boot sequence enabling a computer/set-top box to be reprogrammed when you think you may have bricked it.

I have been designing electronics with this type of technology for 20 years albeit in the early days for military applications where cost was not the same driver as for consumer electronics.

Reply to
alan_m

Yes it has always been an amazement to me that we have not by now got a more sophisticated boot system. We have hardware in the machine capable of a lot, Surely instead of beeping a little recorded message could be sent out saying boot sector not readable or something.It should only resort to bleeps if the motherboard is a going! In my experience when the motherboard is a gonner most of the machine is dead with no sound at all! My suspicion here is a boot problem, one assumes that by holding keys down on boot attempt does not result in any on screen messages. some will, some won't. However first thing to check is all internal cables and the cmos battery. Then I'd suggest its time to try a few more radical things, but you may decide to let a local expert have a look, depends on how old it is. Brian

Reply to
Brian Gaff

Not always true. It really should be, but normally the clock at least needs power and if the year is wrong strange stuff starts to occur often seemingly ending with a no boot situation after an update. No idea why but not enough testing again I expect. Brian

Reply to
Brian Gaff

Not always with watches they take so little current merely some muck or cgrease or corrosion on the battery or contacts can trigger the low battery issue. On PCs though, I think its cables and plugs as I said in my first post here, as it seems not much great design ever goes into these. Most seem to be made by insulation displacement or crimp connections and the fit of many plugs, particularly the power ones seems either so tight you almost pull the drives to bits getting hem off or they fall out at a touch. No middle ground here! Is the machine IDE or sorter? Brian

Reply to
Brian Gaff

main CPU is enough.

Ltes face it, the main CPU controls the upgradeable BIOS that is put into flash.

All it has to do is start as it presumably does with a bios bootloader in ROM, notice that the pins are shorted and load a very basic set of defaults from ROM. And reflash the flash with those defaults.

All it has to do is boot enough to be able to load a basic OS.

Reply to
The Natural Philosopher

That would mean that it would need to have a voice synthesiser that works independently from other hardware that might be faulty. Beep codes are fine for basic problems: all you need is the key to their meaning.

Reply to
Max Demian

then it isnt flash is it?

"flash memory noun : Computing noun: flash memory

a kind of memory that retains data *in the absence of a power supply*."

I am not up to date on modern boards but I would EXPECT that there is a boot ROM bios, upgradeable flash for most of the more exotic parts of the BIOS and if there is battery static RAM, its used to store a very very few configuration variables.

Ones that get overwritten a lot - like what time it was when last booted etc.

Reply to
The Natural Philosopher

Exactly, it's me that's saying I don't think motherboards store the BIOS settings in flash, I think they still use NVRAM.

I accept that they *could* use flash, but has anyone got any evidence that newer boards actually *don't* use NVRAM?

I can still run

hexdump -C /dev/nvram

and see non-random looking values, obviously only the BIOS knows what each bit means for that particular motherboard

00000000 00 00 00 bf ff ff ff 7f 02 ff ff ff ff ff ff ff |................| 00000010 ff ff ff ff ff ff fb ff ff ff fe ff ff ff ff ff |................| 00000020 1b 21 ff ff 20 ff f7 a8 0c ff ff ff ff ff ff ff |.!.. ...........| 00000030 10 b9 00 00 c7 c8 b1 28 ff 00 df 00 00 00 f0 00 |.......(........| 00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000050 00 00 00 00 00 00 00 d0 50 99 25 f5 72 46 ff 00 |........P.%.rF..| 00000060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000070 00 00 |..|
Reply to
Andy Burns

I realised I have a manual for m,y MB.

It has 512bytes of CMOS ram and an RTC kept alive by battery AND a FLASH memory for the bios.

One presumes it has some boot coad in ROM as well.

Reply to
The Natural Philosopher

No the BIOS code/data will all be in flash (along with firmware for e.g onboard ethernet and stuff)

If it's modernish it might have an "A" and "B" half where the one that gets upgraded is not the one you've been using as a failsafe, and the bootblock gets re-written last (and if you're not on a UPS you cross your fingers).

Reply to
Andy Burns

Modern NV devices can have protected areas that can be configured to be one time programmable and can contain factory default boot data. The rest of the device can be used in the way you describe depending on how the software has been written. These devices are software controlled and need a defined sequence of data to defined addresses in order to remove the data lock protection, to erase a page and/or to write new data. After data has been written additional data sequences are used to apply the lock protection again to make them read only (until a new sequences of controls allows writing)

You can even get hybrid devices where on power up data in the slow NV on chip memory is transferred to a faster on chip volatile RAM and on power down the data in the RAM is transferred back to the NV memory. Power for this latter operation is maintained on chip for a second or two by the use of a small capacitor.

Many TV set-top boxes can be reprogrammed but usually there is protected boot sequence that allows reprogramming from scratch. On the set top set top boxes I own on power up (from the mains and not from standby) the box will first check a USB port to see if a file with new software is present. If not it continues to boot in the normal way but if it does find the correct formatted software on a USB stick it offers the option to read it and put it in flash memory. This functionality of always reading the USB port on mains applied power up allows new software to be loaded when the old has been corrupted or if the wrong software update has been attempted. Boxes I've previously owned, 15+ years ago, had similar functionality over USB or RS232 when connected to a computer.

Reply to
alan_m

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