I2C

Detecție EEPROM

Detecția dispozitivelor I2C se face cu comanda:

tom@rpi-yo3iti:~ $ i2cdetect -l

În cazul plăcii mele, ne interesează doar bus-ul i2c-0 pe care am montat un EEPROM la pinii 27 și 28 ai RPi (BCM0 și BCM1).

i2c-1	i2c       	bcm2835 (i2c@7e804000)          	I2C adapter
i2c-11	i2c       	bcm2835 (i2c@7e205000)          	I2C adapter
i2c-0	i2c       	i2c-11-mux (chan_id 0)          	I2C adapter
i2c-10	i2c       	i2c-11-mux (chan_id 1)          	I2C adapter

Apropos, comanda pinout oferă o imagine simpatică cu toții pinii RPi:

tom@rpi-yo3iti:~ $ pinout
,--------------------------------.
| oooooooooooooooooooo J8   +======
| 1ooooooooooooooooooo  PoE |   Net
|  Wi                    oo +======
|  Fi  Pi Model 4B  V1.2 oo      |
|        ,----.               +====
| |D|    |SoC |               |USB3
| |S|    |    |               +====
| |I|    `----'                  |
|                   |C|       +====
|                   |S|       |USB2
| pwr   |HD|   |HD| |I||A|    +====
`-| |---|MI|---|MI|----|V|-------'

Revision           : c03112
SoC                : BCM2711
RAM                : 4096Mb
Storage            : MicroSD
USB ports          : 4 (excluding power)
Ethernet ports     : 1
Wi-fi              : True
Bluetooth          : True
Camera ports (CSI) : 1
Display ports (DSI): 1

J8:
   3V3  (1) (2)  5V    
 GPIO2  (3) (4)  5V    
 GPIO3  (5) (6)  GND   
 GPIO4  (7) (8)  GPIO14
   GND  (9) (10) GPIO15
GPIO17 (11) (12) GPIO18
GPIO27 (13) (14) GND   
GPIO22 (15) (16) GPIO23
   3V3 (17) (18) GPIO24
GPIO10 (19) (20) GND   
 GPIO9 (21) (22) GPIO25
GPIO11 (23) (24) GPIO8 
   GND (25) (26) GPIO7 
 GPIO0 (27) (28) GPIO1 
 GPIO5 (29) (30) GND   
 GPIO6 (31) (32) GPIO12
GPIO13 (33) (34) GND   
GPIO19 (35) (36) GPIO16
GPIO26 (37) (38) GPIO20
   GND (39) (40) GPIO21

Putem scana fiecare bus pentru a vedea ce adrese există în fiecare. Pentru bus-ul 0:

tom@rpi-yo3iti:~ $ i2cdetect -y 0

Dacă comanda nu funcționează și dă erori, se poate adăuga un flag -r astfel:

tom@rpi-yo3iti:~ $ i2cdetect -y -r 0

Comanda afișează:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --

Lista de mai sus conține toate adresele dispozitivului pe bus-ul respectiv, cu --, UU sau adresa dispozitivului ca valoare.

• -- arată că dispozitivul a fost interogat, dar nu a răspuns nici un dispozitiv. Dacă se obține acest răspuns, înseamnă fie că dispozitivul nu este pe bus, fie nu este detectat din cauza anumitor probleme hardware (conexiuni sua tensiuni greșite, altceva).
• UU arată că s-a sărit peste interogarea adresei respective deoarece adresa este utilizată de un driver. Acest lucru indică că dispozitivul este prezent pe bus și că este foarte probabil ca driver-ul să fie corect.
• Adresa unui dispozitiv in hexa arată că a fost detectat. De pildă 50 arată că a fost detectat un dispozitiv la adresa 50.

In both the above cases, hardware side of the device & its connections are all fine. And if it is still not working as expected in case it is showing “UU”, it is high chances that the driver may need tuning / modification. Just to be doubly sure about that, you may verify it by changing the device with an another one, if possible.

And for the case showing the device address in hexadecimal, either a software driver is needed for it or it may be accessed using some user space accessing mechanism.

Note: i2cdetect is part of the i2c-tools package. So, if it is not available on the corresponding Linux system, the i2c-tools package may need to be installed.

I2C Probing

tom@@rpi-yo3iti:~ $ sudo i2cdetect -F 0
Functionalities implemented by /dev/i2c-0:
I2C                              yes
SMBus Quick Command              yes
SMBus Send Byte                  yes
SMBus Receive Byte               yes
SMBus Write Byte                 yes
SMBus Read Byte                  yes
SMBus Write Word                 yes
SMBus Read Word                  yes
SMBus Process Call               yes
SMBus Block Write                yes
SMBus Block Read                 no
SMBus Block Process Call         no
SMBus PEC                        yes
I2C Block Write                  yes
I2C Block Read                   yes

i2cdetect is a userspace program to scan an I²C bus for devices. It outputs a table with the list of detected devices on the specified bus. i2cbus indicates the number or name of the I2C bus to be scanned, and should correspond to one of the busses listed by i2cdetect -l. The optional parameters first and last restrict the scanning range (default: from 0x03 to 0x77).

tom@raspberrypi:~ $ sudo i2cdetect -l
i2c-1	i2c       	bcm2835 (i2c@7e804000)          	I2C adapter
i2c-11	i2c       	bcm2835 (i2c@7e205000)          	I2C adapter
i2c-0	i2c       	i2c-11-mux (chan_id 0)          	I2C adapter
i2c-10	i2c       	i2c-11-mux (chan_id 1)          	I2C adapter

tom@raspberrypi:~ $ sudo i2cdetect -y 0

I2cdetect returns a grid of possible addresses with each device displayed as shown in the screenshot below.

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --

If no devices are detected check that you have followed all the steps at the start of this tutorial for enabling the I²C bus and the devices connected to the Raspberry Pi are powered and do not share the same I²C address.

Programare

C/ C++

Atenție la eroarea de compilare de mai jos:

# make
gcc -g -Wall -c eeprom-tinker.c
gcc -g -Wall -c linux-i2c.c
linux-i2c.c:13:10: fatal error: i2c/smbus.h: No such file or directory
 #include <i2c/smbus.h>
          ^~~~~~~~~~~~~
compilation terminated.
Makefile:12: recipe for target 'linux-i2c.o' failed
make: *** [linux-i2c.o] Error 1

Indică că nu a fost instalat libi2c-dev și se rezolvă prin sudo apt-get install libi2c-dev:

#include <unistd.h>             //Needed for I2C port
#include <fcntl.h>              //Needed for I2C port
#include <sys/ioctl.h>          //Needed for I2C port
#include <linux/i2c-dev.h>      //Needed for I2C port

int file_i2c;
int length;
unsigned char buffer[60] = {0};

// Open the I2C BUS
char *filename = (char*)"/dev/i2c-0";
if ((file_i2c = open(filename, O_RDWR)) < 0) {
        // ERROR_HANDLING
        printf("Failed to open the i2c bus");
        return;
}

Link-uri externe

Documentație

• A nano Cheat Sheet
• SMBus Quick Start Guide — The System Management Bus (SMBus) is a two-wire interface through which various system component chips can communicate with each other and with the rest of the 4 system. It is based on the principles of operation of I2C. SMBus provides a control bus for the system to pass messages to and from devices instead of using individual control lines, helping to reduce pin count and system wires.
• AN10216-01 I2C MANUAL — The I2C Manual provides a broad overview of the various serial buses, why the I2C bus should be considered, technical detail of the I2C bus and how it works, previous limitations/solutions, comparison to the SMBus, Intelligent Platform Management Interface implementations, review of the different I2C devices that are available and patent/royalty information. The I2C Manual was presented during the 3 hour TecForum at DesignCon 2003 in San Jose, CA on 27 January 2003.
• I2C Part 1 - Introducing I2C
• I2C Part 2 - Enabling I²C on the Raspberry Pi
• I2C Part 3 - I²C tools in Linux
• I2C Part 4 - Programming I²C with Python

Specificații

• B+ HAT ID EEPROM Format Specification

Utile

• Device Trees, overlays, and parameters
• Hackaday Raspberry Pi Hat ID EEPROM Details
• Raspberry Pi SPI and I2C Tutorial

Discuții de prin forumuri

• STICKY: HOWTO: Raspi HAT EEPROM and device-tree
• I2C EEPROM not read identically on RPi