RPi 400: Why oh why still no RTC?

[tick999]

I just got my shiny new RPi 400 - great product!

But, in this day and age, it really should have a proper built in Real Time Clock.
And, Yes, I do have a need for it and would use it. Lots of people are attaching them externally to the
GPIO port, where it is exposed. That alone should indicate that there is a demand for this feature.
The hardware seems to be cheap enough, judging by the price of external RTC modules (about $2) on EBay..
So, I'm wondering what the problem is?
You would need a means of replacing the coin cell battery, of course. But I'm sure that could be done.

Someone here suggested creating a dedicated RTC port, where you could plug one in. That would do, right?

[jamesh]

Cost, cost, cost, battery, cost and battery.

[trejan]

The hardware seems to be cheap enough, judging by the price of external RTC modules (about $2) on EBay..

You can't estimate price based on those cheap RTC modules from eBay. It is well known that they're using reclaimed chips from e-waste salvaging operations. They're not new as the bulk price of a new RTC is more than the entire module costs. The exact model of chip you get is somewhat variable as they install what they can get and its not always the same accuracy.

Buy a CM4 + CM4IO and you'll have a RTC.

[fanoush]

Maybe you can stick/solder one to the bottom of the board directly to GPIO pins? when seeing https://www.jeffgeerling.com/blog/2020/ ... and-review - photo https://www.jeffgeerling.com/sites/defa ... shell.jpeg there seems to be some space? The i2c port can have multiple devices connected so the pins on gpio should still be usable (for I2c).

[hippy]

One option would have been to make an RTC an optional extra, sell it as a separate board, much as has been done for the Pi 4B case fan. Adding a header or header holes may not be zero-cost but should be very little.

[HermannSW]

Maybe you can stick/solder one to the bottom of the board directly to GPIO pins? when seeing https://www.jeffgeerling.com/blog/2020/ ... and-review - photo https://www.jeffgeerling.com/sites/defa ... shell.jpeg there seems to be some space? The i2c port can have multiple devices connected so the pins on gpio should still be usable (for I2c).

Thanks for that nice pointer!
Only the black part from top keyboard needs to go in that space, leaving quite some volume of free space.
I see that it is easy to solder to odd numbered GPIO pins.
At least for me soldering to any even numbered pin besides pins 2 and 40 is not possible.
Here is function summary for default pinout on odd numbered pins, that are available for easy soldering.
Pin2 would be interesting to solder to for access to 5V in addition.
I would superglue a part to side of keyboard top black part, that will make it appear in free space automatically.
Perhaps it is time to open my Pi400 and look for more free space inside ...

pi400.space_near_GPIO.jpg

pi400.space_near_GPIO.jpg (95.42 KiB) Viewed 3944 times

[alphanumeric]

I have RTC's installed on several of my Pi's. Almost all of them are headless setups with no Internet access.
While it would be nice to have one internally installed on my Pi400, with my intended use, not having one is no big deal. Mine has Internet access. That being said, I would have happily paid more for my Pi400 if it had a RTC onboard. It would be something I would have no problem paying extra for. Optional or not optional, I would still be happy to pay extra for it.

[tick999]

Gosh, thanks for all the great replies here. Much appreciated.
It looks like some people here would be prepared to pay a little extra for a built in RTC.
Using an I2C chip would seem the most straightforward way to implement this. Just
reserve the two I2C address for RTC use, in the documentation.

A quick scan through the Mouser website gives some indication as to what this might cost:

PCF8563T RTC I2C chip €0.40 Qty:500 [or €0.27ea for a 2.5k piece reel]
20mm Coin Cell Holder €0.21 Qty:500
CR2032 battery €0.66 Qty:500
32kHz XTal €0.41 Qty:500

Total: €1.68

Say, approx double this for extras and assembly - ballpark €3.

Might be an idea to poll the users to see what percentage would be prepared
to shell out an extra €3 or so for an RTC. #include <me>

Thanks to all.

[fanoush]

Say, approx double this for extras and assembly - ballpark €3.

There are ready made modules for similar price. Like e.g. this one https://www.ebay.com/itm/192063696326

Might be an idea to poll the users to see what percentage would be prepared
to shell out an extra €3 or so for an RTC. #include <me>

Definitely makes sense if you plan to start business of reselling Pi400 with preinstalled RTC modules for €3 extra.

[fruitoftheloom]

Gosh, thanks for all the great replies here. Much appreciated.
It looks like some people here would be prepared to pay a little extra for a built in RTC.
Using an I2C chip would seem the most straightforward way to implement this. Just
reserve the two I2C address for RTC use, in the documentation.

A quick scan through the Mouser website gives some indication as to what this might cost:

PCF8563T RTC I2C chip €0.40 Qty:500 [or €0.27ea for a 2.5k piece reel]
20mm Coin Cell Holder €0.21 Qty:500
CR2032 battery €0.66 Qty:500
32kHz XTal €0.41 Qty:500

Total: €1.68

Say, approx double this for extras and assembly - ballpark €3.

Might be an idea to poll the users to see what percentage would be prepared
to shell out an extra €3 or so for an RTC. #include <me>

Thanks to all.

You appear not have taken into account the cost of redesigning the main board to include a RTC as well as an access door to make changing the battery easy.

[jamesh]

Indeed. Cost to redo the plastics to put in a door about £100k, excluding design time. Injection moulding is an expensive business, especially at the quality levels we require. Adding RTC and battery slot on to the board not too difficult, but remember, this is a cost burden that everyone needs to pay, even if they are happy with the current system.

So either we charge £3 (or more) extra, and everyone pays more, or we take the hit on our profit margin and lose £3 per sale. Don't forget, we make more than 20k devices a DAY (over the whole range). So 10 people on here wanting something is NOT a big percentage and you cannot extrapolate.

Personally I've never noticed the lack of an RTC.

[alphanumeric]

My impression, based on forum traffic, is most people are not bothered by there not being a RTC onboard. Your only going to see the scattered i want one comments. I get why its not there and I'm fine with that.
On the other side of the coin I'm one of those few, yes i would like one and would pay extra for it. IMHO there aren't enough of use to warrant the time and investment of adding one from the factory.
Plus, almost all of my setups that have a RTC also have several other i2c devices connected. I'm going to be modifying my setup to add those other breakouts anyway. I usually use a Proto Hat to get access to the GPIO and mount my RTC on that.
IMHO it doesn't hurt to ask, if your polite about it and don't have unrealistic expectations. I mention this as a lot of these type of threads go sideways and get locked.

[GlowInTheDark]

IMHO it doesn't hurt to ask, if your polite about it and don't have unrealistic expectations. I mention this as a lot of these type of threads go sideways and get locked.

The problem is there's not really any way to distinguish between genuine surprise and a mocking tone.

People say things like "Why or why is there no RTC?" and it would be reasonable to assume that it is just genuine surprise - because coming from the world of PCs, it does seem strange to most people that the Pi board has no RTC - but of course, it always gets interpreted by the forum regs as an insult to their precious RPi. And things go south from there...

It doesn't help that a certain RPi official sometimes gets defensive about these things.

Personally, I think that if the RPi had had an RTC builtin from the beginning, things would have been better for everyone and we wouldn't be having this conversation (for the Nth time). Of course, we'd be discussing something else that people think of as "missing" (*), so maybe no actual net gain.

(*) In my case, that would be an on-board x86 co-processor (just kidding, folks...)

[BMS Doug]

Similar posts exist for other features that people feel absolutely have to be included.

Feature bloat happens, until every pi has to include a sychronisation kit for CH3N...

...because we all need a Kit:CH3N Synch with every raspberry pi sold.

By keeping the feature list minimal the raspberry pi foundation can keep the cost low. People who need additional features can add them without everyone having to pay the cost.

[alphanumeric]

It seems to me, that most of the things that would be a PITA to manually add and setup are already there. And hats off to the Pi Foundation for that. IMHO the Pi is pretty feature packed as it is.
For most Pi's adding a RTC isn't that big a deal, lots of them just plug into the GPIO and no soldering required. Just some tweaks to get it working. It may not look so good sticking out the back of a Pi 400 but that's the way it goes some times.

[fanoush]

Personally, I think that if the RPi had had an RTC builtin from the beginning, things would have been better for everyone

The point dicussed over and over is that this in not true. No need for RTC if the Pi is networked or even boot over network. And it is very easy and cheap to add it if you want it. It would also again block extra pins you can now repurpose for something else. it is not jut cost, it is that by adding stuff you take away free gpios - e.g. wifi and bluetooth took UART and SD/MMC pins.

Also the point of Pi is learning stuff, it is a positive thing to learn what RTC is and how it can be connected if you want it. This is not PC that should already have everything out of box to make it easy.

[davidcoton]

Personally, I think that if the RPi had had an RTC builtin from the beginning, things would have been better for everyone

The point dicussed over and over is that this in not true.

+1. Ity would NOT be better for most Pi users whose Pi have access to the internet. It might be better for those building off-net applications, but then the cost of an added RTC is insignificant.

Feature bloat happens, until every pi has to include a sychronisation kit for CH3N...

...because we all need a Kit:CH3N Synch with every raspberry pi sold.

But we have already established that CH3N is impossible, because the current sink capacity of the GPIOs is inadequate.

[hippy]

It would also again block extra pins you can now repurpose for something else. it is not jut cost, it is that by adding stuff you take away free gpios - e.g. wifi and bluetooth took UART and SD/MMC pins.

It wouldn't have to. It could instead be placed on the I2C bus which interfaces with the PMIC, PoE HAT fan controller, or identifies HAT type.

I am sure other solutions which avoided taking anything away from the 40-way header could be found if it were decided to add an RTC or anything else.

This is not PC that should already have everything out of box to make it easy.

<joke>

It's a Linux SBC where things have been left out to make it difficult.

</joke>

[alphanumeric]

All of the RTC modules I have used, DS1307, DS3231, RV3028 use i2c, so all you lose in the process is one i2c address. You can still add other i2c devices, its a shared bus. And if its onboard no GPIO pins are covered / blocked.

[cleverca22]

All of the RTC modules I have used, DS1307, DS3231, RV3028 use i2c, so all you lose in the process is one i2c address. You can still add other i2c devices, its a shared bus. And if its onboard no GPIO pins are covered / blocked.

but those 2 pins are now stuck in i2c mode, you cant use them as gpio anymore
putting it on the gpio0/1 pins would be best, since the hat stuff says those are reserved for i2c, but having it onboard would prevent you from choosing to use them as gpio, and drive up costs

[alphanumeric]

All of the RTC modules I have used, DS1307, DS3231, RV3028 use i2c, so all you lose in the process is one i2c address. You can still add other i2c devices, its a shared bus. And if its onboard no GPIO pins are covered / blocked.

but those 2 pins are now stuck in i2c mode, you cant use them as gpio anymore
putting it on the gpio0/1 pins would be best, since the hat stuff says those are reserved for i2c, but having it onboard would prevent you from choosing to use them as gpio, and drive up costs

Ah, OK, valid point, hadn't thought of that. Mostly because I only ever use them for i2c and use i2c a lot.

[cleverca22]

an internal i2c bus like the pmic one would be a solution to that
but its not broken out to any header, and without schematics its hard to access without tapping into pins on a surface mount part

[incognitum]

Would be more interesting to find more innovative ways to get current time, than mess with batteries.

E.g. I recall the wifi chip used has a FM radio block as well (although I recall not in an usable state, the relevant pin not connected to an antenna).
Would it theoretically be possible to pluck the time from a RDS radio station if that was made to work?

[trejan]

an internal i2c bus like the pmic one would be a solution to that
but its not broken out to any header, and without schematics its hard to access without tapping into pins on a surface mount part

You need to do more than just adding a RTC to the internal I2C bus. You also need a new firmware mailbox to communicate with it and a new Linux Pi RTC driver to talk to the firmware. Firmware and kernel both trying to use the same I2C controller would be bad.

GPIO0/1 on the header is also used for DPI so adding the RTC there isn't ideal either.

Would be more interesting to find more innovative ways to get current time, than mess with batteries.

E.g. I recall the wifi chip used has a FM radio block as well (although I recall not in an usable state, the relevant pin not connected to an antenna).
Would it theoretically be possible to pluck the time from a RDS radio station if that was made to work?

That just sounds like a huge kludge. Please enter a radio station frequency in your area that has RDS, extend the antenna and move the Pi near a window to enable time sync.

[incognitum]

That just sounds like a huge kludge. Please enter a radio station frequency in your area that has RDS, extend the antenna and move the Pi near a window to enable time sync.

Here (in continental Europe) virtually all FM radio stations have RDS.
So seeking for any station with a signal should do.