FpWrite to an i2c device doesn't work properly
lazarus / 32-Linux

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jpelletier · 2014-06-13 04:19

On Linux, using lazarus and free pascal, I'm trying to use the I2C
device by opening /dev/i2c-7 which is a dongle on a parallel port.
Hardware is known good and has been tested with known good software. A
bus pirate connected on the I2c port detects the peripherals
correctly.

With the following code, Fpwrite sends 4 bytes 'F0'  instead of
sending the 'A' at the slave address 20 (a PCF8574).
The result is the same on the bus pirate as sniffer and on an
oscilloscope. I have the same result if I use FileWrite instead of
FpWrite.

  I2c_Address: integer;
  test: string;

  I2c_Address := $20;
  test := 'A';
  // handle has been opened correctly, no error reported

  if FpIOCtl(handle,I2C_SLAVE, pointer(I2c_Address)) < 0 then ...
  // Slave address is set correctly, no error reported
...
...

  Fpwrite(handle,test,1);

Any ideas? Thanks!

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marcov · 2014-06-13 07:37

Write test[1], "test"  is the address where the pointer is stored,
since an ansistrings are dynamic

you might also want fpwrite for EINTR and repeat if that occurs.

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avra · 2014-06-13 09:59

You have a working I2C code for DS1307 RTC here:
http://forum.lazarus.freepascal.org/index.php/topic,17500.msg96610.htm
l#msg96610

There is a hardware abstraction lib for Raspberry Pi Linux. You can
take a look here:
http://forum.lazarus.freepascal.org/index.php/topic,20991.msg127025.ht
ml#msg127025
http://wiki.freepascal.org/Lazarus_on_Raspberry_Pi#Accessing_external_
hardware

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jpelletier · 2014-06-14 07:19

I added some code for checking.

  WriteLn('Write: Handle = ',I2c_Handle);
  Write := FpWrite(I2c_Handle, 'test', 4);
  if Write = -1 then Perror('I2cWrite',fpgeterrno);

Write: Handle = 20 // Handle corresponds with the one returned by
fpopen
I2cWrite: No such device or address // output of PError