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Example of non-blocking coding style:

This slide/section not lectured in 2017/18.

(Have seen blocking style on earlier slide.)

Example: Non-blocking (untimed) transactor for the four-phase handshake. Non-examinable Part II CST. 
  bool nb_putbyte_start(char d)
  {
    if (ack) return false;
    data = d;
    settle(); // A H/W delay for skew issues, 
    // or a memory fence in S/W for 
    // sequential consistency.
    req = 1;
    return true;
  }

  bool nb_putbyte_end(char d)
  {
    if (!ack) return false;
    req = 0;
    return true;
  }

  bool nb_getbyte_start(char &r)
  {
    if (!req) return false;
    r = data;
    ack = 1;
    return true;
  }
  
  bool nb_getbyte_end()
  {
    if (req) return false;
    ack = 0;
    return true;
  }

Both routines should be repeatedly called by the client until returning true.

14: (C) 2008-18, DJ Greaves, University of Cambridge, Computer Laboratory.