I2C fun

I realized quickly that the MultiAVR library is only the core Arduino library. What is missing are the non-core ones, like the I²C library (AKA TWI or “Wire”). Expecting a serious re-write, I was pleasantly surprised to see that I had to make exactly one change:

*** /usr/share/arduino/libraries/Wire/utility/twi.c     2011-01-10 14:28:07.000000000 +0900
--- /home/harald/workspace/BlinkSanguino/utility/twi.c  2011-09-24 22:38:53.283676108 +0900
***************
*** 69,74 ****
--- 69,77 ----
      // as per note from atmega8 manual pg167
      sbi(PORTC, 4);
      sbi(PORTC, 5);
+   #elif defined(__AVR_ATmega644P__) || defined(__AVR_ATmega1284P__)
+     sbi(PORTC, 0);
+     sbi(PORTC, 1);
    #else
      // activate internal pull-ups for twi
      // as per note from atmega128 manual pg204

and that was it.

In one day I was able to talk to:

1. the LCD (16×2 characters)
2. an PCF8574A (8 bit I/O)
3. an PCF8583 (RTC)
4. an MCP23017 (16 bit I/O)