real time clock on Raspberry Pi B+

mjosh · 10-12-2014, 07:20 AM

I want to buy an RPi and I need a real time clock (RTC). I've found many fine RTCs but it's not so straightforward.

RasClock seems nice but requires a custom module and their instructions assume Raspbian. Other RTCs don't require any custom modules but I'm still not sure if another dristro than Raspbian can handle them. Some RTCs add a physical challenge: they might require soldering (which I don't want to do), or they might add physical volume to the RPi and thus make the use of a plastic case a challenge.

So I need to hear a success story from someone who has actually done this.

There is a nice howto for ChronoDot but ChronoDot falls in the the 'physical challenge' category of RTCs. Now, I have a hope that the i2c tools used in the howto can make RasClock work. But I'm not sure.

So, what RTC have you had working on an RPi running Slackware?

rtmistler · 10-13-2014, 09:58 AM

RasClock supports either a deb package or the kernel module. There's no assumption you have to use Raspbian.

I've found that this RTC works pretty well https://learn.adafruit.com/adding-a-...ry-pi?view=all mainly because the Dallas Semiconductor chips seem to be more supported by systems as defaults. Doesn't mean that the NXP chips aren't also (one the RasClock uses) I just have no experience with that one.

I would read that second link to determine if the clock is visible to your I2C. Likely if you're running a distribution which supports the Pi, it should have drivers to see I2C devices and a real time clock module, then it becomes a question of configuring it to work. For that I think the Adafruit reference may be helpful. The RasClock is good because it's all set up to plug right into the Pi.

mjosh · 10-21-2014, 05:55 AM

Quote:

Originally Posted by rtmistler

RasClock supports either a deb package or the kernel module.

So... if I just find the source for modules i2c-bcm2708 and rtc-pcf2127a and compile them in Slackware, I'll be okay?

On the side of this, I downloaded and extracted the kernel RasClock provides for Raspbian, linux-image-3.6.11-atsw-rtc_1.1_armhf.deb, and I found the two modules inside:

Code:

$ find -type f | grep i2c-bcm2708
./lib/modules/3.6.11-atsw-rtc+/kernel/drivers/i2c/busses/i2c-bcm2708.ko

$ find -type f | grep rtc-pcf2127a
./lib/modules/3.6.11-atsw-rtc+/kernel/drivers/rtc/rtc-pcf2127a.ko

But I understand that I can't use .ko files with Slackware. They're compiled against different headers.

rtmistler · 10-21-2014, 06:12 AM

I would give compilation a try. It's probably just one of the modules which will work for you, but I'm not sure which.

mjosh · 10-21-2014, 06:29 AM

Great! Thanks!

One more question. Where do I find these modules in source form?

rtmistler · 10-21-2014, 06:44 AM

Haven't had to locate the source myself, I either had the modules already there or was able to use the DEB package, this blog appears to have a link in git hub, but I'm not so sure it looks like a lot more than just module sources to me. It does say the words "Currently the module requires the installation of a driver that is not in the standard Raspbian distribution." Sorry, best to perform a web search and see what you can find, I also didn't read that blog entry tediously, just happened to do a quick search.

Actually if you go down their tree into drivers/rtc, you see that there are files for the pcf clock, as well as a number of other ones.