Hello,
I’m trying to work through the I2C examples in the Molloy book. But I’m using a Honeywell HMC6352 compass since I had one lying around. It can work from 2.7V to 5V and operates at a bus frequency of 100KHz. I verified that it works by hooking it up to a 5V microcontroller. I can query its registers. But I haven’t had any luck communicating with it on a BeagleBone Black.
I’m using 3.9V pull-up resistors for SDA and SCL. Here is info about my kernel version, cape slots, and the I2C pins:
debian@beaglebone:~$ uname -a
Linux beaglebone 4.4.54-bone16 #1 Fri Mar 17 04:56:31 UTC 2017 armv7l GNU/Linux
debian@beaglebone:~$ sudo cat $SLOTS
0: PF---- -1
1: PF---- -1
2: PF---- -1
3: PF---- -1
4: P-O-L- 0 Override Board Name,00A0,Override Manuf,cape-universaln
debian@beaglebone:~$ config-pin -i P9.19
Pin is not modifyable: P9_19 i2c2_scl
debian@beaglebone:~$ config-pin -i P9.20
Pin is not modifyable: P9_20 i2c2_sda
debian@beaglebone:~$
It looks like everything is okay. Am I missing any steps? I saw some info about adding an I2C overlay. Is that still necessary with the universal cape?
BTW, I also tried the 4.4.54-ti-r93 kernel without success.
Thanks for any advice. This noob is stumped. 
the i2c port on P9_19/P9_20 is already enabled by default.
Regards,
Thank you for the reply.
As a sanity check, I went back to Debian 7.5. And it just worked without having to do any extra configuration. See below for a dump of results. My compass device appears at its default address 0x21. I sent a command (0x72) to read EEPROM register 0x00 and read back the expected byte (0x42).
With the Debian 8.7 image, I got error messages when I tried the i2cget and i2cset commands. I also noticed that the i2cdetect -y -r 1 command runs very slowly compared to the Debian 7.5 image, it takes a second or so to print each address entry.
Is there some extra configuration I need to do in Debian 8.7? Like edit the uEnv.txt file? Load an overlay? Or tweak a DTS file?
Thanks!
debian@beaglebone:~$ uname -a
Linux beaglebone 3.8.13-bone50 #1 SMP Tue May 13 13:24:52 UTC 2014 armv7l GNU/Linux
debian@beaglebone:~$ i2cdetect -y -r 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: – -- – -- – -- – -- – -- – -- –
10: – -- – -- – -- – -- – -- – -- – -- – --
20: – 21 – -- – -- – -- – -- – -- – -- – --
30: – -- – -- – -- – -- – -- – -- – -- – --
40: – -- – -- – -- – -- – -- – -- – -- – --
50: – -- – -- UU UU UU UU – -- – -- – -- – --
60: – -- – -- – -- – -- – -- – -- – -- – --
70: – -- – -- – -- – --
debian@beaglebone:~$ i2cset -y 1 0x21 0x72 0x00
debian@beaglebone:~$ i2cget -y 1 0x21
0x42
Wrong bus..
With 3.8.13 the i2c bus #'s where setup on a first come basis..
With newer kernel's the bus #'s actually corresponds to the i2c bus
#.. In this case: &i2c2..
So use:
i2cdetect -y -r 2
Regards,
Derp! That did the trick. (See test output below. It prints the expected default values from my sensor.)
Thanks again.
debian@beaglebone:~$ uname -a
Linux beaglebone 4.4.54-ti-r93 #1 SMP Fri Mar 17 13:08:22 UTC 2017 armv7l GNU/Linux
debian@beaglebone:~$ gcc compass.c
debian@beaglebone:~$ ./a.out
Starting HMC6352 Compass Test.
EEPROM reg[0x00] = 0x42
EEPROM reg[0x01] = 0x00
EEPROM reg[0x02] = 0x00
EEPROM reg[0x03] = 0x00
EEPROM reg[0x04] = 0x00
EEPROM reg[0x05] = 0x01
EEPROM reg[0x06] = 0x04
EEPROM reg[0x07] = 0x06
EEPROM reg[0x08] = 0x50