The RTC Cape provides time tracking capability for the BeagleBone Black even when the power is lost. This cape features the MCP79410 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.
- Device tree files: BBB-RTC-01-00A1.tar.gz
- Latest software for BeagleBone Black can be downloaded here.
The instructions below are performed on Angstrom release 2013.09.04 (Linux beaglebone 3.8.13 #1 SMP Wed Sep 4 09:09:32 CEST 2013 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:
tar xzvf 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 MCP79410 is registered as rtc1:
dmesg | tail
- [ 2016.295415] bone-capemgr bone_capemgr.8: slot #10: 'Override Board Name,00A1,Override Manuf,BBB-RTC-01'
- [ 2016.295721] bone-capemgr bone_capemgr.8: slot #10: Requesting part number/version based 'BBB-RTC-01-00A1.dtbo
- [ 2016.295777] bone-capemgr bone_capemgr.8: slot #10: Requesting firmware 'BBB-RTC-01-00A1.dtbo' for board-name 'Override Board Name', version '00A1'
- [ 2016.296256] bone-capemgr bone_capemgr.8: slot #10: dtbo 'BBB-RTC-01-00A1.dtbo' loaded; converting to live tree
- [ 2016.299751] bone-capemgr bone_capemgr.8: slot #10: #3 overlays
- [ 2016.311744] omap_i2c 4802a000.i2c: bus 2 rev0.11 at 100 kHz
- [ 2016.352020] rtc-ds1307 2-006f: rtc core: registered mcp7941x as rtc1
- [ 2016.352091] rtc-ds1307 2-006f: 64 bytes nvram
- [ 2016.352225] omap_i2c 4802a000.i2c: unable to select pin group
- [ 2016.352428] bone-capemgr bone_capemgr.8: slot #10: 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
- Mon Jan 1 00:00:02 2001 0.000000 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 Dec 13 22:51:56 2013 0.000000 seconds
Followings are some specifications of the RTC Cape:
|Size||2.15" x 2.825"|
Please visit Where To Buy for a list of distributors who carry BeagleBoardToys' capes.
RTC Cape Revision A1