The RTC Cape provides time tracking capability for the BeagleBone Black even when the power is lost. This cape features the DS1338 I2C-based real-time clock/calendar and a holder for a coin battery type CR2032. Setup, reading, and setting up time is easy with the provided device tree overlay.
Initial release of RTC Cape.
Software Support & Compatibility
- All revisions are compatible with BeagleBone and BeagleBone Black using 3.8 kernel.
- Latest software for BeagleBone Black can be downloaded here.
The instructions below are performed on Debian release 2014-05-14 (Linux beaglebone 3.8.13-bone50 #1 SMP Tue May 13 13:24:52 UTC 2014 armv7l GNU/Linux).
- Connect your BeagleBone Black to the internet, log in as root, download the device tree files and extract them to /lib/firmware of your BBB:
cd /lib/firmware wget https://github.com/CircuitCo/RTC-Cape/raw/docs/BBB-RTC-01-00A1.tar.gz tar xvzf BBB-RTC-01-00A1.tar.gz
- Load the device tree overlay for your RTC Cape:
echo BBB-RTC-01:00A1 > /sys/devices/bone_capemgr*/slots
- Check to ensure the overlay is loaded. In the messages below, the DS1338 is registered as rtc1:
dmesg | tail [ 5721.844355] bone-capemgr bone_capemgr.9: slot #7: 'Override Board Name,00A1,Override Manuf,BBB-RTC-01' [ 5721.844607] bone-capemgr bone_capemgr.9: slot #7: Requesting part number/version based 'BBB-RTC-01-00A1.dtbo [ 5721.844656] bone-capemgr bone_capemgr.9: slot #7: Requesting firmware 'BBB-RTC-01-00A1.dtbo' for board-name 'Override Board Name', version '00A1' [ 5721.847380] bone-capemgr bone_capemgr.9: slot #7: dtbo 'BBB-RTC-01-00A1.dtbo' loaded; converting to live tree [ 5721.848460] bone-capemgr bone_capemgr.9: slot #7: #3 overlays [ 5721.860065] omap_i2c 4802a000.i2c: bus 2 rev0.11 at 100 kHz [ 5721.902076] rtc-ds1307 2-0068: rtc core: registered ds1338 as rtc1 [ 5721.902147] rtc-ds1307 2-0068: 56 bytes nvram [ 5721.902274] omap_i2c 4802a000.i2c: unable to select pin group [ 5721.902468] bone-capemgr bone_capemgr.9: slot #7: Applied #3 overlays.
- Read the time from the RTC chip. It should look like something below since the time has not been set:
hwclock -r -f /dev/rtc1 Sat 01 Jan 2000 12:06:17 AM UTC -1.004531 seconds
- Update the system time of the BeagleBone Black (internet connection required) and write that to the RTC chip using hwclock command:
ntpdate -b -s -u pool.ntp.org hwclock -w -f /dev/rtc1
- Read the time again. This time it should have been updated.
hwclock -r -f /dev/rtc1 Fri 16 May 2014 10:57:12 PM UTC -0.755959 seconds
Followings are some specifications of the RTC Cape:
|Size||2.15" x 2.825"|
|Squarewave Output Pin||GPIO1_29|
Please visit Where To Buy for a list of distributors who carry BeagleBoardToys' capes.
RTC Cape Revision A1
- Bill of Materials
- Manufacturing Files
- Schematic (PDF)
- Schematic (EAGLE) (Right click and save as...)
- PCB (EAGLE) (Right click and save as...)
To download all files at once please click here
To go back to the cape list, please click here