DEFINITION MODULE RS232Code;
(*
    High-speed interrupt-driven input/output via the serial port


Derived from the Lilith Modula-2 system developed by the
group of Prof. N. Wirth at ETH Zurich, Switzerland.


  This module provides interrupt-driven I/O via the serial port,
  but the Interrupt Service Routine is implemented using in-line
  code (as opposed to IOTRANSFER).

  This approach is NOT portable to other Modula-2 implementations,
  but it allows for treatment of interrupts with high frequency.
  There is a buffer of at least 128 characters for received data.
*)


EXPORT QUALIFIED Init, StartReading, StopReading,
                 BusyRead, Read, Write;


PROCEDURE Init (baudRate: CARDINAL; stopBits: CARDINAL;
                parityBit: BOOLEAN; evenParity: BOOLEAN;
                nbrOfBits: CARDINAL; VAR result: BOOLEAN);
(*- Initialize the serial port.
in:     baudRate        transmission speed,
        stopBits        number of stop bits (usually 1 or 2),
        parityBit       if TRUE, parity is used, otherwise not,
        evenParity      if parity is used, this indicates even/odd,
        nbrOfBits       number of data bits (usually 7 or 8),
out:    result          TRUE if the initialization was completed.

The legal values for the parameters depend on the implementation
(e.g. the range of supported baud rates).
*)

PROCEDURE StartReading;
(*- Allow characters to be received from the serial port.

This procedure initializes the communication controller to
generate interrupts upon reception of a character. It also
un-masks the corresponding interrupt level in the interrupt
controller.
*)

PROCEDURE StopReading;
(*- Disable receiving from the serial port.

A call to this procedure disables the communication controller
from generating interrupts. In addition it terminates the
coroutine which listens to the line. The old interrupt vector
as well as the old state of the interrupt controller (mask)
is restored.
*)

PROCEDURE BusyRead (VAR ch: CHAR; VAR received: BOOLEAN);
(*- Read a character from serial port, if one has been received.
out:    ch              the character received, if any,
        received        TRUE if a character was received.

If no character has been received, ch = 0C, received = FALSE.
*)

PROCEDURE Read (VAR ch: CHAR);
(*- Read a character from the serial port.
out:    ch      the character received.

As opposed to BusyRead, Read waits for a character to arrive.
*)

PROCEDURE Write (ch: CHAR);
(*- Write a character to the serial port.
in:     ch      character to send.

Note: no interpretation of characters is made.
*)

END RS232Code.
