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Support for 'write_then_readfrom' #7

Merged
merged 3 commits into from
Apr 3, 2019
Merged

Support for 'write_then_readfrom' #7

merged 3 commits into from
Apr 3, 2019

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StevenBruinen
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Added support for the busio 'write_then_readfrom' function as some i2c devices require this (e.g. the Adafruit i2c FRAM module)

@StevenBruinen
Support for 'write_then_readfrom'
ce80342 
Added support for the busio 'write_then_readfrom' function as some i2c devices require this (e.g. the Adafruit i2c FRAM module)
@ladyada
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ladyada commented Apr 3, 2019

lgtm, @caternuson wanna try it out?

@caternuson
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I'm not seeing this used in the FRAM library:
https://github.com/adafruit/Adafruit_CircuitPython_FRAM/blob/master/adafruit_fram.py
Can you show where this is. Or, even better, provide an example showing how the TCA and FRAM are not working together?

@ladyada
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ladyada commented Apr 3, 2019

https://github.com/adafruit/Adafruit_CircuitPython_FRAM/blob/master/adafruit_fram.py#L210 ?

@caternuson
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Thought that might be the intention here. But PR is writeto_then_readfrom. Was it suppose to be write_then_readinto?

But also, I think my code comment here is wrong:
https://github.com/adafruit/Adafruit_CircuitPython_TCA9548A/blob/master/adafruit_tca9548a.py#L53
The TCA is more of a passthru for busio.i2c, not i2c_device. The key bit being the override of try_lock to insert the channel switch:
https://github.com/adafruit/Adafruit_CircuitPython_TCA9548A/blob/master/adafruit_tca9548a.py#L65
which gets called by i2c_device's context manager here:
https://github.com/adafruit/Adafruit_CircuitPython_BusDevice/blob/master/adafruit_bus_device/i2c_device.py#L175

Went ahead and wired up a TCA and I2C FRAM and it's currently working OK:

Adafruit CircuitPython 3.1.2 on 2019-01-07; Adafruit ItsyBitsy M4 Express with samd51g19
>>> import board, busio
>>> import adafruit_tca9548a
>>> import adafruit_fram
>>> i2c = busio.I2C(board.SCL, board.SDA)
>>> tca = adafruit_tca9548a.TCA9548A(i2c)
>>> fram = adafruit_fram.FRAM_I2C(tca[1])
>>> fram[0] = 1
>>> fram[0] 
bytearray(b'\x01')
>>>

@ladyada
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ladyada commented Apr 3, 2019

maybe a typo? :) you hit the issue on raspberry pi more because it cant do repeated start in two commands

@StevenBruinen
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With the new code the FRAM module works ok on my RaspberryPi.
Without it I get the error below when running:

try:
  import adafruit_fram
  fram = adafruit_fram.FRAM_I2C(tca[1])
  logging.info('FRAM memory: Module active.')
except Exception as e:
    logging.exception('FRAM memory: Module not responding.')

Traceback (most recent call last):
  File "/home/pi/MainProgram.py", line 50, in <module>
    fram = adafruit_fram.FRAM_I2C(tca[1])
  File "/usr/local/lib/python3.5/dist-packages/adafruit_fram.py", line 211, in __init__
    read_buf, stop=False)
  File "/usr/local/lib/python3.5/dist-packages/adafruit_bus_device/i2c_device.py", line 167, in write_then_readinto
    self.readinto(in_buffer, start=in_start, end=in_end)
  File "/usr/local/lib/python3.5/dist-packages/adafruit_bus_device/i2c_device.py", line 97, in readinto
    self.i2c.readfrom_into(self.device_address, buf, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/adafruit_tca9548a.py", line 76, in readfrom_into
    return self.tca.i2c.readfrom_into(address, buffer, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/busio.py", line 55, in readfrom_into
    return self._i2c.readfrom_into(address, buffer, stop=stop)
  File "/usr/local/lib/python3.5/dist-packages/adafruit_blinka/microcontroller/generic_linux/i2c.py", line 44, in readfrom_into
    readin = self._i2c_bus.read_bytes(address, end-start)
  File "/usr/local/lib/python3.5/dist-packages/Adafruit_PureIO/smbus.py", line 155, in read_bytes
    return self._device.read(number)
OSError: [Errno 121] Remote I/O error

@caternuson
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Oh, I see what's going on. It's to support this:
https://github.com/adafruit/Adafruit_CircuitPython_BusDevice/blob/master/adafruit_bus_device/i2c_device.py#L150
Things are conditionally different in write_then_readinto. It went down the other branch since there is no writeto_then_readfrom, which doesn't work as @ladyada pointed out. So gets the I/O Error.

@caternuson
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@StevenBruinen Thanks. Set this up on a Pi and got same error. Tested your fix and it works.

Can you add a code comment to the function similar to this:
https://github.com/adafruit/Adafruit_CircuitPython_BusDevice/blob/8a5b9974cda321771941f2e69513c9cee13e07fb/adafruit_bus_device/i2c_device.py#L154
which might help highlight this as a linuxy specific thing in the future.

@StevenBruinen
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Great!
I've added the comment as requested.

@StevenBruinen StevenBruinen reopened this Apr 3, 2019
@StevenBruinen
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Sorry, I think I did something wrong now but I don't know what.
This is my first pull request ever... :-)

caternuson
caternuson requested changes Apr 3, 2019
View reviewed changes
adafruit_tca9548a.py Outdated
@@ -81,6 +81,12 @@ def writeto(self, address, buffer, **kwargs):
raise ValueError("Device address must be different than TCA9548A address.")
return self.tca.i2c.writeto(address, buffer, **kwargs)

def writeto_then_readfrom(self, address, buffer_out, buffer_in, **kwargs):
"""Pass thru for writeto_then_readfrom."""
"""In linux, at least, this is a special kernel function call"""
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Travis isn't liking the two string literals back to back. Could make it one docstring, but I'd say just change this to:

# In linux, at least, this is a special kernel function call

@caternuson
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Awesome! Thanks for finding this and submitting the fix.

Look ma, no I/O errors:

pi@raspberrypi:~ $ python3
Python 3.5.3 (default, Sep 27 2018, 17:25:39) 
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import board, busio
>>> import adafruit_tca9548a
>>> import adafruit_fram
>>> i2c = busio.I2C(board.SCL, board.SDA)
>>> tca = adafruit_tca9548a.TCA9548A(i2c)
>>> fram = adafruit_fram.FRAM_I2C(tca[1])
>>> fram[0] = 0x10
>>> fram[0]
bytearray(b'\x10')

@StevenBruinen
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Cool! Solved for everybody now \0/
Thank you all for your support!

@caternuson caternuson merged commit 33280a6 into adafruit:master Apr 3, 2019
@StevenBruinen StevenBruinen deleted the patch-1 branch April 3, 2019 18:52
adafruit-adabot added a commit to adafruit/Adafruit_CircuitPython_Bundle that referenced this pull request Apr 4, 2019
@adafruit-adabot
Automated update by Adabot (adafruit/adabot@52a9ec7)
20a3902 
Updating https://github.com/adafruit/Adafruit_CircuitPython_TCA9548A to 0.2.0 from 0.1.2:
  > Merge pull request adafruit/Adafruit_CircuitPython_TCA9548A#7 from StevenBruinen/patch-1
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@caternuson caternuson caternuson approved these changes

@ladyada ladyada ladyada approved these changes

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@StevenBruinen @ladyada @caternuson