Document pin usage of Ethernet library. [imported]

[cmaglie]

This is Issue 662 moved from a Google Code project.
Added by 2011-10-01T18:34:38.000Z by go4s...@gmail.com.
Please review that bug for more context and additional comments, but update this bug.
Closed (Fixed).

Original labels: Type-Defect, Priority-Medium, Component-Docs

Original description

I am programming an Arduino Mega (ATmega1280) with the ether network module (WIZnet WIZ811MJ) (http://www.sparkfun.com/products/9473).
I am using the SPI and Ethernet libraries.
According to http://arduino.cc/en/Main/ArduinoBoardMega the Arduino MEGA's SPI pins are 50 (MISO), 51 (MOSI), 52 (SCK), 53 (SS).
But if I look at the code that manipulates SS arduino-0022\libraries\Ethernet\utility\w5100.h (line 311):

#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
  inline static void initSS()    { DDRB  |=  _BV(4); };
  inline static void setSS()     { PORTB &= ~_BV(4); };
  inline static void resetSS()   { PORTB |=  _BV(4); };
#else
  inline static void initSS()    { DDRB  |=  _BV(2); };
  inline static void setSS()     { PORTB &= ~_BV(2); };
  inline static void resetSS()   { PORTB |=  _BV(2); };
#endif

The code addresses PORT B pin 4 (PB4) which is Arduino MEGAs pin 10 (and NOT 53).
For the Arduino MEGAs PORT B pin 0 (PB0) should be used to get pin 53.

I changed the code to:

#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
  inline static void initSS()    { DDRB  |=  _BV(0); };
  inline static void setSS()     { PORTB &= ~_BV(0); };
  inline static void resetSS()   { PORTB |=  _BV(0); };
#else
  inline static void initSS()    { DDRB  |=  _BV(2); };
  inline static void setSS()     { PORTB &= ~_BV(2); };
  inline static void resetSS()   { PORTB |=  _BV(2); };
#endif

and now SPI works as advertised: 50 (MISO), 51 (MOSI), 52 (SCK), 53 (SS).