/*------------------------------------------------------------------------------
SIO.C:  Serial Communication Routines.

Copyright 1995-2002 KEIL Software, Inc.
------------------------------------------------------------------------------*/

#include <reg51.h>
#include <string.h>
#include "sio.h"

/*------------------------------------------------------------------------------
Notes:

The length of the receive and transmit buffers must be a power of 2.

Each buffer has a next_in and a next_out index.

If next_in = next_out, the buffer is empty.

(next_in - next_out) % buffer_size = the number of characters in the buffer.
------------------------------------------------------------------------------*/
#define TBUF_SIZE   64           /*** Must be one of these powers of 2 (2,4,8,16,32,64,128) ***/
#define RBUF_SIZE   8           /*** Must be one of these powers of 2 (2,4,8,16,32,64,128) ***/

#define TBUF_SPACE  idata       /*** Memory space where the transmit buffer resides ***/
#define RBUF_SPACE  idata       /*** Memory space where the receive buffer resides ***/

#define CTRL_SPACE  data        /*** Memory space for the buffer indexes ***/

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
#if TBUF_SIZE < 2
#error TBUF_SIZE is too small.  It must be larger than 1.
#elif TBUF_SIZE > 128
#error TBUF_SIZE is too large.  It must be smaller than 129.
#elif ((TBUF_SIZE & (TBUF_SIZE-1)) != 0)
#error TBUF_SIZE must be a power of 2.
#endif

#if RBUF_SIZE < 2
#error RBUF_SIZE is too small.  It must be larger than 1.
#elif RBUF_SIZE > 128
#error RBUF_SIZE is too large.  It must be smaller than 129.
#elif ((RBUF_SIZE & (RBUF_SIZE-1)) != 0)
#error RBUF_SIZE must be a power of 2.
#endif

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
static TBUF_SPACE unsigned char tbuf [TBUF_SIZE];
static RBUF_SPACE unsigned char rbuf [RBUF_SIZE];

static CTRL_SPACE unsigned char t_in = 0;
static CTRL_SPACE unsigned char t_out = 0;

static CTRL_SPACE unsigned char r_in = 0;
static CTRL_SPACE unsigned char r_out = 0;

static bit ti_restart = 0;  /* NZ if TI=1 is required */


/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
static void com_isr (void) interrupt 4
{
/*------------------------------------------------
Received data interrupt.
------------------------------------------------*/
if (RI != 0)
  {
  RI = 0;

  if (((r_in - r_out) & ~(RBUF_SIZE-1)) == 0)
    {
    rbuf [r_in & (RBUF_SIZE-1)] = SBUF;
    r_in++;
    }
  }

/*------------------------------------------------
Transmitted data interrupt.
------------------------------------------------*/
if (TI != 0)
  {
  TI = 0;

  if (t_in != t_out)
    {
    SBUF = tbuf [t_out & (TBUF_SIZE-1)];
    t_out++;
    ti_restart = 0;
    }
  else
    {
    ti_restart = 1;
    }
  }

}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
#pragma disable

void com_initialize (void)
{
/*------------------------------------------------
Setup TIMER1 to generate the proper baud rate.
------------------------------------------------*/
com_baudrate (1200);

/*------------------------------------------------
Clear com buffer indexes.
------------------------------------------------*/
t_in = 0;
t_out = 0;

r_in = 0;
r_out = 0;

/*------------------------------------------------
Setup serial port registers.
------------------------------------------------*/
SM0 = 0; SM1 = 1;   /* serial port MODE 1 */
SM2 = 0;
REN = 1;            /* enable serial receiver */

RI = 0;             /* clear receiver interrupt */
TI = 0;             /* clear transmit interrupt */
ti_restart = 1;

ES = 1;             /* enable serial interrupts */
PS = 0;             /* set serial interrupts to low priority */
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
#pragma disable

void com_baudrate (
  unsigned baudrate)
{
/*------------------------------------------------
Clear transmit interrupt and buffer.
------------------------------------------------*/
TI = 0;             /* clear transmit interrupt */
t_in = 0;           /* empty transmit buffer */
t_out = 0;

/*------------------------------------------------
Set timer 1 up as a baud rate generator.
------------------------------------------------*/
TR1 = 0;            /* stop timer 1 */
ET1 = 0;            /* disable timer 1 interrupt */

PCON |= 0x80;       /* 0x80=SMOD: set serial baudrate doubler */

TMOD &= ~0xF0;      /* clear timer 1 mode bits */
TMOD |= 0x20;       /* put timer 1 into MODE 2 */

TH1 = (unsigned char) (256 - (XTAL / (16L * 12L * baudrate)));

TR1 = 1;            /* start timer 1 */
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
#pragma disable

char com_putchar (
  unsigned char c)
{
/*------------------------------------------------
If the buffer is full, return an error value.
------------------------------------------------*/
if (com_tbuflen () >= TBUF_SIZE)
  return (-1);

/*------------------------------------------------
Add the data to the transmit buffer.  If the
transmit interrupt is disabled, then enable it.
------------------------------------------------*/
tbuf [t_in & (TBUF_SIZE - 1)] = c;
t_in++;

if (ti_restart)
  {
  ti_restart = 0;
  TI = 1;               /* generate transmit interrupt */
  }

return (0);
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
#pragma disable

int com_getchar (void)
{
if (com_rbuflen () == 0)
  return (-1);

return (rbuf [(r_out++) & (RBUF_SIZE - 1)]);
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
#pragma disable

unsigned char com_rbuflen (void)
{
return (r_in - r_out);
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
#pragma disable

unsigned char com_tbuflen (void)
{
return (t_in - t_out);
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/