Difference between revisions of "OneWire GPIO bus Master"

Latest revision as of 14:49, 19 September 2017

Informations and HOWTOs for Armadeus OneWire support.

Authors: JanosA/JulienB

Supported boards and software versions

• Use the latest Armadeus GIT/SF repository or the latest stable release.
• Currently, with APF28 modules, only the APF28Dev board is supported, but it's easy to add support to another boards. (Check linux-2.6.35.3/arch/arm/mach-mx28/apf28dev.c file)
• Following instructions were also successfully tested on OPOS6ULDev with bitbanging OneWire Linux emulation (GPIO). Indeed i.MX6UL doesn't have hardware OneWire master. Please note that using GPIO bitbanging reduces a lot the maximum length of 1Wire cable that can be used !!

Software installation

• If not done by default, recompile your Linux kernel with OneWire GPIO bus master (and some slave device) support.

$ make linux-menuconfig

Device Drivers  --->
    <*> Dallas's 1-wire support  --->
        1-wire Bus Masters  --->
            <*> GPIO 1-wire busmaster
        1-wire Slaves  --->
            <*> Thermal family implementation

$ make

• Reflash your Linux kernel

Hardware Notes

APF28Dev	OPOS6ULDev
Connect the OneWire slave directly to the APF28_DEV board J9 connector: * Vcc 3.3V is pin 1 on J9 connector * DQ is pin 31 on J9 (LCD_D18 / GPIO 1_18) * GND is pin 39 on J9 Add an 1.2k pull-up resistor between Vcc and DQ	Connect the OneWire slave on RPi2/3 compatible J3 connector: 3.3V is pin 1 of J3 DQ is pin 40 of J3 GND is pin 6 of J3 Add an 4,7k pull-up resistor between 3.3V and DQ

How it works

Warning: GPIO bitbanging method used here is not compatible with frequency scaling, so, if activated, you have to switch to performance governor, otherwise your 1-wire bus might mis-function after system boot... Otherwise you may have problems to detect devices and see in dmesg: w1_master_driver w1_bus_master1: w1_search: max_slave_count 64 reached, will continue next search.

The OneWire bus master driver every 10 seconds scan the bus for new slave devices.

Each detected OneWire slave device have a sub-directory with it's unique ID in "/sys/devices/w1 bus master".

The sub-directory format is <2 digit family ID>-<12 digit unique ID>.

# ls -la /sys/devices/w1\ bus\ master/
total 0
drwxr-xr-x    4 root     root             0 Jan  1 01:06 .
drwxr-xr-x    6 root     root             0 Jan  1 01:05 ..
drwxr-xr-x    3 root     root             0 Jan  1 01:06 28-000001e68904
lrwxrwxrwx    1 root     root             0 Jan  1 01:07 driver -> ../../bus/w1/drivers/w1_master_driver
drwxr-xr-x    2 root     root             0 Jan  1 01:07 power
lrwxrwxrwx    1 root     root             0 Jan  1 01:07 subsystem -> ../../bus/w1
-rw-r--r--    1 root     root          4096 Jan  1 01:07 uevent
-rw-rw-rw-    1 root     root          4096 Jan  1 01:07 w1_master_add
-r--r--r--    1 root     root          4096 Jan  1 01:07 w1_master_attempts
-r--r--r--    1 root     root          4096 Jan  1 01:07 w1_master_max_slave_count
-r--r--r--    1 root     root          4096 Jan  1 01:07 w1_master_name
-r--r--r--    1 root     root          4096 Jan  1 01:07 w1_master_pointer
-rw-rw-rw-    1 root     root          4096 Jan  1 01:07 w1_master_pullup
-rw-rw-rw-    1 root     root          4096 Jan  1 01:07 w1_master_remove
-rw-rw-rw-    1 root     root          4096 Jan  1 01:07 w1_master_search
-r--r--r--    1 root     root          4096 Jan  1 01:07 w1_master_slave_count
-r--r--r--    1 root     root          4096 Jan  1 01:07 w1_master_slaves
-r--r--r--    1 root     root          4096 Jan  1 01:07 w1_master_timeout

You can list the detected slaves from this files:

# cat /sys/devices/w1\ bus\ master/w1_master_slave_count
1
# cat /sys/devices/w1\ bus\ master/w1_master_slaves
28-000001e68904

Let's read the temperature: (The 28-xxx family is a DS18B20 temperature sensor in this example.)

# cat /sys/devices/w1\ bus\ master/28-000001e68904/w1_slave
dd 01 4b 46 7f ff 03 10 1e : crc=1e YES
dd 01 4b 46 7f ff 03 10 1e t=29812

The t=29812 means, the temperature is: 29.812°C

Tested sensors

• Waterproof DS18B20

Links

• Fr:Mesure de température avec DS18B20 sur RPi