/* port_id.c    1/18/89   Louis Shay

   National Semiconductor Corporation
   Microcomuputer Systems Division
   Microcontroller Applications Group

   Program to identify the presence and type of UART in a system.
   This program will query the serial port at global port address
   "int ubase", and return a value that identifies what type of UART
   is present at that address. This address is set by the calling program
   prior to the function call. The returned int values are:

     0, if there is no identifiable UART at that port address.
     1, if the port type is INS8250, INS8250-B.
     2, if the port type is INS8250A, INS82C50A, NS16450, NS16C450.
     3, if the port type is NS16550A.
     4, if the port type is NS16C552.

  note: the main source file should include "ns16550a.h". This is the
  device header file.
*/
#include <stdio.h>
#include <conio.h>
#include "ns16550a.h"

int port_id()
{
  extern int ubase;                     /* reference global address */


  /* 1. test general functionality. Is the core register set present? */


  wrLCR( 0xaa );
  if( rdLCR() != 0xaa )         /* test LCR register & set DLAB=1 */
    return( 0 );

  /* as an identifier, UART address 1 is 8-bits (DLM) when LCR7=1 (DLAB).
     UART address 1 is 4-bits (IER) when DLAB=0. */

  wrDLM( 0x55 );                        /* test for DLM present (8-bits) */
  if( rdDLM() != 0x55 )
    return( 0 );
  wrLCR( 0x55 );                        /* LCR: set DLAB = 0 */
  if( rdLCR() != 0x55 )
    return( 0 );
  wrIER( 0x55 );                        /* test for IER present (4-bits) */
  if( rdIER() != 0x05 )
    return( 0 );
  wrFCR( 0 );                           /* FIFOs off, if present */
  wrIER( 0 );                           /* interrupts off, IIR should be 01 */
  if( rdIIR() != 1 )
    return( 0 );

  /* test modem control register address. Should be 5-bits wide */

  wrMCR( 0xf5 );                        /* 8-bit write */
  if( rdMCR() != 0x15 )                 /* expect 5-bit read */
    return( 0 );

  /* test MCR/MSR loopback functions */

  wrMCR( 0x10 );                        /* set loop mode */
  (void)rdMSR();                        /* clear out delta bits */
  if( ( rdMSR() & 0xf0 ) != 0 )         /* check state bits */
    return( 0 );
  wrMCR( 0x1f );                        /* toggle modem control lines */
  if( ( rdMSR() & 0xf0 ) != 0xf0 )      /* check state bits */
    return( 0 );
  wrMCR( 0x03 );                        /* exit loop mode, DTR, RTS active */

  /* 2. port id successful at this point. determine port type */

  wrSCR( 0x55 );                        /* is there a scratch register? */
  if( rdSCR() != 0x55 )
    return( 1 );                        /* no SCR, type = INS8250 */

  wrFCR( 0xcf );                        /* enable FIFO's, if present */
  if( ( rdIIR() & 0xc0 ) != 0xc0 )      /* check FIFO ID bits */
    return( 2 );                        /* no FIFO's, type = NS16450 */
  wrFCR( 0 );                           /* turn off FIFO's */

  wrLCR( 0x80 );                        /* set DLAB */
  wrAFR( 0x07 );                        /* write to AFR */
  if ( rdAFR() != 0x07 ) {              /* read AFR */
     wrLCR( 0x00 );                        /* reset DLAB */
     return ( 3 );                      /* if not the same, type = NS16550A */
   }
  wrAFR( 0x00);                         /* clear AFR */
  wrLCR( 0x00 );                        /* reset DLAB */
  return ( 4 );                         /* type = NS16C552 */
}