The BeagleBoneBlack comes with an "internal" EEPROM connected to i2c-0
line. I can see that clearly when I do i2cdetect:
debian@beaglebone:~$ i2cdetect -y -r 0
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: UU -- -- -- -- -- -- --
It is showing under address 0x50. When I try to do ahexdump I get the
following values with no issue:
sudo hexdump -C /sys/class/i2c-dev/i2c-0/device/0-0050/eeprom | head -5
00000000 aa 55 33 ee 41 33 33 35 42 4e 4c 54 30 30 30 43
|.U3.A335BNLT000C|
00000010 31 38 33 37 42 42 42 47 30 36 32 32 ff ff ff ff
|1837BBBG0622....|
00000020 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
|................|
*
00001000 aa 55 33 ee 41 33 33 35 42 4e 4c 54 30 30 30 43
|.U3.A335BNLT000C|
Now I want to add another EEPROM (with cape) on i2c-2 line which is
supported according to [BBB
SRM](https://cdn-shop.adafruit.com/datasheets/BBB_SRM.pdf) section 8.2. It
is the CAT24C256 as mentioned in the SRM. The allowable address range for
the expansion cards is 0x54-0x57. When I do i2cdetect I can see the
following:
debian@beaglebone:~$ i2cdetect -r -y 2
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- UU UU UU UU -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
I can see the addresses 0x54-0x57 showing, but when I try hex dump I get an
error:
hexdump: /sys/class/i2c-dev/i2c-2/device/2-0054/eeprom: Connection
timed out
Questions:
1. Why are they showing as U's not actual address numbers? I know U stands
for used resource?
2. Why am I failing to read from that EEPROM? I have tried all addreses
from 0x54-0x57 with no luck. I can confirm that those addresses are showing
in /sys/class/i2c-dev/i2c-2/device and the each dir has the following in it:
debian@beaglebone:~$ ls /sys/class/i2c-dev/i2c-2/device/2-0054/ -la
total 0
drwxr-xr-x 4 root root 0 Oct 26 19:46 .
drwxr-xr-x 8 root root 0 Oct 26 19:46 ..
drwxr-xr-x 3 root root 0 Oct 26 19:47 2-00540
lrwxrwxrwx 1 root root 0 Oct 26 19:47 driver ->
../../../../../../bus/i2c/drivers/at24
-rw------- 1 root root 32768 Oct 26 19:47 eeprom
-r--r--r-- 1 root root 4096 Oct 26 19:47 modalias
-r--r--r-- 1 root root 4096 Oct 26 19:47 name
lrwxrwxrwx 1 root root 0 Oct 26 19:47 of_node ->
../../../../../../firmware/devicetree/base/ocp/i2c@4819c000/cape_eeprom0@54
drwxr-xr-x 2 root root 0 Oct 26 19:47 power
lrwxrwxrwx 1 root root 0 Oct 26 19:47 subsystem ->
../../../../../../bus/i2c
-rw-r--r-- 1 root root 4096 Oct 26 19:47 uevent
I can see the addresses mapping into the kernel but when I try to hexdump
eeprom it doesn't work at all. I though this was supposed to be setup by
kernel since it is mentioned in BeagleBone SRM. Am I going to need an
overlay to add to uboot for this? It doesn't make sense since i2c-2 is
already set up by default i.e. when I connect another device at address
aside from 0x54-0x57 it shows up fine and I'm able to interface to it?
All I'm trying to do is read from the EEPROM like I did with the "internal"
one to confirm it is working. What am I doing wrong?
--
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