// digi3b.c

// The following are known only to the functions that follow them. 
// They can't be modified or even accessed by anything above this point.
unsigned base;
unsigned switch_port;
unsigned ppi_porta;
unsigned ppi_portb;
unsigned ppi_portc;

// set up the ppi according to the dictates of the mode argument
void set_up_ppi(int mode)
{
  unsigned control = base + 0x23;
  int command;

  command = (mode & 0x0c) << 1; // shift bits 2 and 3 into positions 3 and 4
  command += (mode & 3); // add in bits 0 and 1
  command |= 0x80; // OR in bit 7 for PPI set up

  outp(control, command); // set according to mode command

} // end set_up_ppi(..)


// get the port -- in the future, this will grow into an auto-detect function
void get_port(void)
{
  base = 0x300;
  switch_port = base + 0x18;
  ppi_porta = base + 0x20;
  ppi_portb = base + 0x21;
  ppi_portc = base + 0x22;
} // end get_port()


// end digi3b.c