Python I2C... Almost all working, but

Duo
1

So thanks to a few people on here ( especially hanahKobain ) for pointing me in helpful directions… I built an image including “pinpong” and was able to actually create a python app, that runs upon boot and displays IP addresses (and time) on an SSD1306 display.
BUT… there seems to be a problem with using i2c.scan() under pinpong.
Not sure why, but it does NOT show all available i2c devices on bus1.
Yet if I do, “i2cdetect -r 1 -y” from terminal, it shows all available i2c devices.
i2c.scan seems to have a limited range of devices it looks for.
Anyone know HOW to make i2c.scan() look at ALL i2c addresses?

Also, when I change the bus from 1 to 2 (there is a valid i2cdev-2 on my boards as I can see devices on it when I do i2cdetect -r 2 -y.), it gives me an error saying I can only use 0,1,2 busses???

Here is the output from an example app supplied with pinpong (with a little modification where I attempted to detect devices by looping thru addresses and attempting i2c.read_byte(device)…

[root@milkv-duo]~# python i2c_scan2.py
milkv-duo

| ____ _ ____ |
| / __ ()__ / __ ____ ____ ____ _ |
| / // / / __ / // / __ / __ / __ `/ |
| / / / / / / / // / / / / // / |
|// /// /// _// //_, / |
| v0.5.2 Designed by DFRobot // |
|_______________________________________|

<pinpong.board.Board object at 0x3fc2a40fd0>

I2C Devices:

00: – – – – – – – – – – – – – – – –
10: – – – – – – – – – – – – – – – –
20: – – – – – – – – – – – – – – – –
30: – – – – – – – – – – – – – – – –
40: – – – – – – – – – – – – – – – –
50: – – – – – – – – – – – – – – – –
60: – – – – – – – – – – – – – – – –
70: – – – – – – – – – – – – – – –
Done

[ 9461.515397] i2c i2c-1: adapter quirk: no zero length (addr 0x003d, size 0, write)
[ 9461.524653] i2c i2c-1: adapter quirk: no zero length (addr 0x003e, size 0, write)
[ 9461.533619] i2c i2c-1: adapter quirk: no zero length (addr 0x003f, size 0, write)
[ 9461.542900] i2c i2c-1: adapter quirk: no zero length (addr 0x0040, size 0, write)
[ 9461.551585] i2c i2c-1: adapter quirk: no zero length (addr 0x0041, size 0, write)
[ 9461.561077] i2c i2c-1: adapter quirk: no zero length (addr 0x0042, size 0, write)
[ 9461.569747] i2c i2c-1: adapter quirk: no zero length (addr 0x0043, size 0, write)
[ 9461.578991] i2c i2c-1: adapter quirk: no zero length (addr 0x0044, size 0, write)
[ 9461.587663] i2c i2c-1: adapter quirk: no zero length (addr 0x0045, size 0, write)
[ 9461.597157] i2c i2c-1: adapter quirk: no zero length (addr 0x0046, size 0, write)
i2c list:
0x3C

==========================

here is the output from “i2cdetect -r 1 -y”,

==========================
[root@milkv-duo]~# i2cdetect -r 1 -y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: – – – – – – – – – – – – –
10: – – – – – – – – – – – – – – – –
20: – – – – – – – – – – – – – – – –
30: – – – – – – – – – – – – 3c – – –
40: – – – – – – – – 48 – – – – – – –
50: – – – – – – – – – – – – – – – –
60: – – – – – – – – 68 – – – – – – –
70: – – – – – – – –

==========================

OledStats
OledStats1920×2550 598 KB

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2

I’m sure this is because some argument of that scan method disables scanning extra range by default.

How does I²C scanning usually work? You scan all 127 addresses on the bus and see what echoes back; but I guess this scanning either doesn’t scan the whole range, or it doesn’t actually scan it.

3

Also, is it Duo 256M? It must be one. Judging by your other thread, at least.

4

Yeah, it’s a 256M.
Interestingly, I can scan I2C devices if I use SMBus, but not thru pinpong.

Yeah, the way you do it is to enumerate thru a range of device addresses and within a try…except block you attempt a write_byte(addr, 0x00) to the device address.
If no device responds… you get the except and there is no device.
If no except, there is a device.

Fairly simple.
Just don’t understand WHY i2c.scan() isn’t getting all the devices, just 0x3C.

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5

Here the code using SMBus.

import time
from smbus import SMBus

#--------------------------

def i2cdetect():
global bus

i2clist = []
for i in range(0x03, 0x77)  :
    try:
        bus.write_byte(i, 0x00)
        i2clist.append(i)
    except:
        pass

return i2clist

#----------------

bus = SMBus(1)

#----------------

i2clist = i2cdetect()

print(‘\nI2C Devices Found:’)
for addr in i2clist:
print(‘0x%02X’ % addr)

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6

I’m actually trying to find out where it is located in the source files, the pinpong lib, the heck.

duo-buildroot-sdk-v1/buildroot-2021.05/package/python-pinpong/pinpong/board.py:

class I2C:
  def __init__(self, board=None, bus_num=0):
    if isinstance(board, int):
      bus_num = board
      board = gboard
    elif board == None:
      board = gboard
    self.board = board
    if self.board.i2c[bus_num] == None:
      self.bus_num = bus_num
    
    if bus_num not in board.res["i2c"]["busnum"]:
      raise ValueError("i2c does not support this device%d"%bus_num, "Supports the i2c device list",board.res["i2c"]["busnum"])
    self.board.i2c[bus_num] = eval(self.board.res["i2c"]["class"] + "(board, bus_num)")
    self.obj = self.board.i2c[bus_num]
    
  def scan(self):
    return self.obj.scan()

And for Milk-V Duo boards this spawns a number of LinuxI2C instances:

class LinuxI2C:
  def __init__(self, board, bus_num=1):
    self.bus_num = bus_num
    self.i2c = I2CTrans(bus_num)

  def scan(self):
    plist=[]
    ack=[1]
    for i in range(1,127):
      try:
        ack = self.i2c.transfer(writing(i, ack))
        plist.append(i)
      except:
        pass
    return plist
7

And yeah, it seems that the SMBus driver does this job a little different.
AFAIK, SMBus is an I²C extension, although it looks weird that you can detect something similar via I²C using a trashduino µC, yet this board doesn’t allow you that via I²C.

Oh, and I recall when I saw it mentioning it works like that on Duo:

Usage: i2cdetect -l | -F I2CBUS | [-ya] [-q|-r] I2CBUS [FIRST LAST]

Detect I2C chips

	-l	List installed buses
	-F BUS#	List functionalities on this bus
	-y	Disable interactive mode
	-a	Force scanning of non-regular addresses
	-q	Use smbus quick write commands for probing (**default**)
	-r	Use smbus read byte commands for probing
	FIRST and LAST limit probing range

That is, i2cdetect will detect them only using SMBus read for probing.

8

OK… now THAT is interesting. If I just do ‘i2cdetect 1 -y’, I don’t get ANY devices (on i2cdev-1). But if I add the ‘-r’ option… it uses SMBus to do a write to the device… and gives me all my devices.
So, guess I say… SCREW using i2c.scan() and stick with my own i2cdetect scan implemented using SMBus.
I never tried the ‘-a’ option. I wonder what that will do… Just tried it. Didn’t do squat.

I’ve used SMBus before, with Raspberry Pi, when I was working on a project (at Honeywell Security) involving Apple (HomeKit (sic)). We were trying to implement their authentication chip into an alarm panel (running linux)… so I tested my concepts out on a Pi and I did it with SMBus.

Thanks for looking deeper, then I cared too. :wink:

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