[fpc-pascal] FPC/Lazarus on RPi4 - How to read/write I2C connected EEPROM?

[Jeffrey A. Wormsley]

I noticed you put the part number in the original email.

Interestingly, the data sheet mentions 64 byte pages, and 1,000,000 erase
cycles, but does not mention the need to erase a page before writing.  So
perhaps this part does not have that restriction.

If you're making a library specifically for this part, then I guess you
don't have to worry about this.  If you're making a library for generic
eeprom support, I think you might want to consider that not all parts
behave this way.

Jeff



On Mon, Apr 3, 2023 at 8:42 AM Jeffrey A. Wormsley <daworm at gmail.com> wrote:

> i2c_read_reg works too inasmuch as it does not error out, but it returns FF
>> whatever addres I read like the i2c-tools command does.
>> I am not sure that it is correct though...
>>
>
> Yes this is expected, as eeproms erase to $FF.  You can write to the same
> byte as many times as you want, as long as you only change 1 bits to 0
> bits.  If you must change a 0 bit to a 1 bit, you have to erase back to $FF
> first.  Be aware that erase means erasing the entire page, and not just a
> single byte.  This is where things like "wear leveling" come into play,
> because a page can only be erased a limited number of times (it used to be
> around 10,000, but maybe newer devices have extended this).  How you manage
> writes to eeprom can be tricky, best to use them for things that don't
> change very often, such as configuration data.
>
> Jeff
>
> On Sun, Apr 2, 2023 at 3:30 PM Bo Berglund via fpc-pascal <
> fpc-pascal at lists.freepascal.org> wrote:
>
>> On Sun, 2 Apr 2023 07:31:43 +0200, Christo Crause via fpc-pascal
>> <fpc-pascal at lists.freepascal.org> wrote:
>>
>> >On Sat, Apr 1, 2023 at 9:57?PM Bo Berglund via fpc-pascal <
>> >fpc-pascal at lists.freepascal.org> wrote:
>> >
>> >> Question:
>> >> Can I use Linux file system commands to read/write the data on the i2c
>> >> EEPROM
>> >> memory device and if so how from fpc?
>> >>
>> >
>> >To some extent it is possible to handle i2c transactions as file
>> read/write
>> >operations, but some ioctl calls are required to configure e.g. the
>> device
>> >address [1]. Take note that only a subset of i2c functionality is
>> available
>> >using read/write calls. Lazi2cdev [2] uses this approach.
>> >
>> >For finer control over the i2c transactions (for example combined
>> >write/read transactions) low level ioctl calls are available in Linux.  I
>> >wrote an i2c class [3] using this approach.
>> >
>> >1. https://www.kernel.org/doc/html/latest/i2c/dev-interface.html
>> >2. https://github.com/laz2wiringpi/lazI2cdev/blob/master/i2cdev_base.pas
>> >3. https://github.com/ccrause/rpiplc_pas/blob/main/native/i2c.pas
>>
>> Hello again!
>>
>> I have now tested the two demos in github [3] and they seem to work OK.
>>
>> The i2cscan works and shows exactly the same as sudo i2cdetect -y 1 does
>> from
>> the i2c-tools package I installed via apt.
>>
>> i2c_read_reg works too inasmuch as it does not error out, but it returns
>> FF
>> whatever addres I read like the i2c-tools command does.
>> I am not sure that it is correct though, for that I need to create an
>> i2c_write
>> demo app first so I can write values at different locations and read them
>> back.
>> The EEPROM has until now not been used so it is in its factory state with
>> no
>> data.
>>
>> Is there a reason that there is no i2c_write_reg demo in the github
>> package?
>>
>> I will try to write one so I can test that as well...
>>
>>
>> --
>> Bo Berglund
>> Developer in Sweden
>>
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>
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