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This topic comprises 3 pages: 1 2 3
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Author
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Topic: DOLBY DSS/DSP 100 lost time/date
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 03-01-2019 09:11 PM
I can't see a SuperCap close to the socketed and soldered in cells on ICPs. Also, if the cert battery is soldered in, having a backup supercap doesn't make much sense.
My NEC manual is not actually clear on that:
'The coin battery (Panasonic BR2330) mounted on the ICP board provides electrical power for maintaining tamper detection,time, and date information while the power to the projector is off. If the battery voltage drops, the tamper detection circuit is activated and the security key is erased. Once the security key has been erased, the projector requires repair at the factory'
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'• Although data is maintained while the battery is being replaced for approximately 3 hours by the sub-battery built into the ICP board (when the sub-battery is fully charged), please replace the battery quickly. To ensure that the sub-battery is fully charged, turn the projector power supply on for 30 minutes or more before replacing the battery'
Now, the trouble is, who's interested in messing around with a working ICP to find out what's happening if...
- Carsten
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 03-04-2019 02:28 AM
I've recently pulled the ICP in our DP4K-19B as part of a cleaning job. It has two of those BR2330 batteries close together, one is supposed to be the "RTC battery", without a backup, and the other the "Certificate battery", with a backup.
I'm not sure what IC on the board is holding the certificates, but it doesn't necessarily have to be close to the battery cells.
Also, if the capacitor designed to provide the backup to just the piece of memory that keeps the certificates alive for about 3 hours, you probably don't need a "supercap", but an ordinary capacitor might do the trick already.
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 03-04-2019 11:45 AM
Many things CAN be repaired. The question is, who would do it?! Barco hasn't the best credit there, and, we have all seen the issues with bricked enigma boards. Many cinemas paid for replacements when suddenly TI fixed it in software...
Is the lost ICP cert a TI thing, or can each OEM rebrain their ICPs?
Also, this is most certainly not field-doable, so, screens will be down, even if some company feels ready to perform the operation?
- Carsten
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 03-04-2019 04:18 PM
Not with that specific number. It's a bit strange that both are the same type, one soldered in, one replaceable. Then again, they may experience different amounts of current drain, and the one keeping the time is not so critical. Also Harold once mentioned that very low current drains can be problematic with cell holders, so a soldered in battery might be safer for a critical very low current source.
I think Doremis IMS1000 features a soldered-in rechargabe button cell sustaining certificate memory. You do not have to replace it periodically, but as every rechargable cell, it has a limited life span (around 10 years they say - moot point, as I hardly doubt any IMS1000 will make 10 years...).
So, what is better?
Also, so far the industry has been rather lucky with their suppliers - but what if a manufacturer goes out of business and there is no 'generic' replacement possible, because the certificate restore hardware is not there?
- Carsten
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 03-04-2019 05:09 PM
A non-rechargeable battery usually outlasts a rechargeable battery in longevity on a "single charge" compared to a rechargeable battery of the same volume.
I guess they simply expect the "certificate battery" to outlast the useful life of the board. But it's for sure this board does have a ticking self-destruct bomb.
The RTC circuit will most likely be more power hungry. You need to drive an electronic oscillator and the circuit that calculates and updates the time and date. That will probably consume more power than simply keeping some memory alive, while there is no external power.
I don't really understand why there needs to be an off-line powered RTC on there. Can't the ICP pull the time from the projector? Does it need to know what the time is when powered down? There is no circuitry alive that can write to log files anyway?
The whole security chain is built on just a select few entities having access to stuff like certain certificates and private keys. Once they disappear, so will the ability to repair those products.
In this particular case, the ICP is actually a TI board, but I doubt Texas Instruments would ever honor a repair request. The certificates in there could also be manufacturer-specific. Has anybody ever tried the ICP across manufacturers? I guess the thing is sufficiently expensive not to try such an experiment, in order to brick it.
So, if the manufacturer would cease to exist or simply decides to entirely abandon it, with it would go the ability to replace it.
This is hardly avoidable and also not, in any way, illegal. But, what is an interesting case though, is that we've almost clearly established that this board does have an expiration date, although it's unclear when exactly that will be. Also, there is no real solution to fix it, as that's being blocked on purpose.
You could ask yourself if it's actually legal to sell such products, without explicitly informing the customer about it.
Now, there might be an infinite amount of nuances, depending on your jurisdiction, but in general, products with a non-advertised built-in auto-expire self-destruct are considered defective...
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 03-05-2019 09:20 AM
I remember the Qube Cinema dilemma. Didn't they eventually issue a "last update" which extended the certificate for another 10 or so years?
quote:
This drives me nuts. With the level of technology we implement today they still insist on using the same silicon RTC implementation designed for the first digital watches in the late 60s. That oscillator drives counters which break time into seconds, minutes, hours, day of month, month, and year. All of that takes power. When all we need is a 64-bit millisecond counter. Every OS first reads that RTC and calculates the millisecond count since some epoch. That math is cumbersome in and by itself and could be avoided. Dumb!
Well, couldn't agree more on that. Actually, I'm pretty particular when it comes down to time and time-keeping... most of this stuff has been implemented in awkward fashions and the circuitry of any RTC should just be a simple 64 bit integer that's increased with "1" every millisecond, which would also keep power usage at a minimum.
I've been a fan of TAI64 timestamps for a while now. It's based on International Atomic Time, which, in contrary to UTC, isn't affected by leap-seconds.
As you might know, leap seconds are a pretty big problem, especially if we are "inserting time", skipping over a second or a half isn't such a problem, but encountering the same timestamp twice, is bound to break stuff, especially in things like databases, that create unique transaction IDs based on timer values.
TAI64 uses a bunch of simple system libraries to convert "atomic time" into "meat space time".
Obviously, those libraries need to be maintained and need to be made aware of new leap seconds, or the clock will skew over time. Then again, every now and then some local dictator moves themselves to another timezone or some government takes the wise decision to mess around with daylight saving time, so those libraries need constant maintenance anyway.
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Harold Hallikainen
Jedi Master Film Handler
Posts: 906
From: Denver, CO, USA
Registered: Aug 2009
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posted 03-05-2019 09:46 AM
In recent products, I've been using a 1 Hz interrupt in the microcontroller to generate a 32 bit signed time stamp. NTP is run at power up and on an occasional basis to initialize the counter and to update it. When doing an update from NTP, I adjust the period register in the right direction to correct the clock speed. Eventually corrections become very rare. This is used in non-secure products like the LSS-200. The clock is used only in logging. There, the time stamp is stored in a 64 bit field. When the log is displayed, a user defined time zone offset and DST offset is applied before passing the integer into time.c for conversion to ASCII for display. I currently do DST determination in javascript on the web UI which then passes a DST flag back to the web server in the device. I am looking for a solution to the 2038 issue where the 32 bit signed counter rolls over (goes negative).
In media blocks, as I've mentioned before, and as Carsten wrote recently, we have had problems with battery holders with very low currents. Therefore, we are now soldering batteries in. Further, super capacitors do not hold enough energy to run the security chip for a long time. In our latest design, we do use a super capacitor to power the security chip. That keeps the chip from drawing any power from the battery for about 2 weeks after main power shutdown. In a typical theater, the battery will never see any drain from the security chip.
The security chip holds the private key, includes an RTC that is used to authorize KDMs. The security chip also has inputs for the tamper switches. A fair amount of current goes through these tamper switches resulting in more battery (or super capacitor) drain. Switches have the same issue as battery holders with very low currents. We run higher currents through the switches when main power is present to prevent the very low current issues. When a tamper occurs, the security chip records the time of the tamper and the type of tamper. There's more stuff going on in the security chip, but that's a fair amount of it.
Harold
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