Category : Modula II Source Code
Archive   : M2EXA20.ZIP
Filename : RS232.MOD

IMPLEMENTATION MODULE RS232;

(* (C) Copyright 1987 Fitted Software Tools. All rights reserved.

This module is part of the example multitasking communications program
provided with the Fitted Software Tools' Modula-2 development system.

Registered users may use this program as is, or they may modify it to
suit their needs or as an exercise.

If you develop interesting derivatives of this program and would like
to share it with others, we encourage you to upload a copy to our BBS.
*)

(* $L+ *)
(* $S-, $R-, $T- *)

FROM SYSTEM IMPORT ASSEMBLER, ADR, ADDRESS, SEG, OFS;
FROM System IMPORT TermProcedure, GetVector, ResetVector;
FROM Storage IMPORT ALLOCATE, DEALLOCATE, Available;
FROM ASCII IMPORT CtrlS, CtrlQ;
FROM Kernel IMPORT InitSignal, NewProcess, Signal, WaitIO;

CONST
Com1IntNo = 12; (* COM1 interrupt vector *)
Com2IntNo = 11; (* COM2 interrupt vector *)

(* 8250 ports *)
RX = 0; (* xmit reg. when DLAB = 0 *)
TX = 0; (* rcv reg. when DLAB = 0 *)
DivL = 0; (* baud rate divisor when DLAB = 1 *)
DivH = 1; (* " " " when DLAB = 1 *)
IntEna = 1; (* interrupt enable *)
IntId = 2; (* interrupt id *)
LCR = 3; (* line status register *)
MCR = 4; (* modem control register *)
LSR = 5; (* line status register *)
MSR = 6; (* modem status register *)

TYPE BufferPointer = POINTER TO ARRAY [0..65531] OF CHAR;

VAR ComPort :CARDINAL; (* Com port in use *)
ComIntNo :CARDINAL; (* Int # for port in use *)
ComBase :CARDINAL; (* base io adrs for port in use *)
ComRX :CARDINAL; (* receive register *)
ComLSR :CARDINAL; (* line status register *)

OldCom1Int :ADDRESS; (* save old ISR adrs here *)
OldCom2Int :ADDRESS;
Com1Base :CARDINAL; (* base ports of 8250 ACA *)
Com2Base :CARDINAL;

ISR1active :BOOLEAN; (* ISR process created? *)
ISR2active :BOOLEAN;

(* Receive buffer *)
BuffPtr :BufferPointer;
BuffSize :CARDINAL;
InPtr :CARDINAL;
OutPtr :CARDINAL;
InCount :CARDINAL;

xon :BOOLEAN; (* use xon/off ? *)
XoffThreshold :CARDINAL;
XonThreshold :CARDINAL;
XoffSent :BOOLEAN;


MODULE RS232Receiver[3];
(*
RS232Receiver runs at priority 3. The actual COM priority is
either 3 or 4, depending on the port in use.
*)

IMPORT ASSEMBLER, WaitIO, Signal, RS232Input,
ComIntNo, ComBase, LSR, RX, TX, MCR, LCR, IntEna,
BuffSize, BuffPtr, InCount, InPtr, xon, CtrlS,
XoffThreshold, XoffSent;

EXPORT ComInt1, ComInt2, StartReading, StopReading;

(*
Even though we have one ISR for each COM port, only one
of those ports may be active at any one time!
*)
PROCEDURE ComInt1;
(*
ISR for COM1
*)
BEGIN
StartReading;
LOOP
WaitIO( 12 );
ASM
MOV BX, ComBase (* read line status reg *)
LEA DX, [BX+LSR]
IN AL, DX
TEST AL, 1 (* input character? *)
JZ exit
LEA DX, [BX+RX] (* grab input character *)
IN AL, DX
MOV CX, InCount (* does it fit in the buffer? *)
CMP CX, BuffSize
JAE exit
LES DI, BuffPtr (* buffer with it! *)
MOV BX, InPtr
MOV ES:[DI+BX], AL
INC InCount (* adjust counters *)
INC BX
CMP BX, BuffSize
JB ok
XOR BX, BX
ok: MOV InPtr, BX
TEST xon, 1 (* xon/xoff enabled ? *)
JZ exit
CMP CX, XoffThreshold
JB exit
TEST XoffSent, 1
JNZ exit
MOV BX, ComBase (* send XOFF is xmit reg empty *)
LEA DX, [BX+LSR]
IN AL, DX
TEST AL, 20H
JZ exit
MOV AL, CtrlS
LEA DX, [BX+TX]
OUT DX, AL
MOV XoffSent, 1

exit:
MOV AL, 20H (* send EOI *)
OUT 20H, AL
END;
IF InCount > 0 THEN Signal( RS232Input ) END;
END;
END ComInt1;


PROCEDURE ComInt2;
(*
ISR for COM2
*)
BEGIN
StartReading;
LOOP
WaitIO( 11 );
ASM
MOV BX, ComBase (* read line status reg *)
LEA DX, [BX+LSR]
IN AL, DX
TEST AL, 1 (* input character? *)
JZ exit
LEA DX, [BX+RX] (* grab input character *)
IN AL, DX
MOV CX, InCount (* does it fit in the buffer? *)
CMP CX, BuffSize
JAE exit
LES DI, BuffPtr (* buffer with it! *)
MOV BX, InPtr
MOV ES:[DI+BX], AL
INC InCount (* adjust counters *)
INC BX
CMP BX, BuffSize
JB ok
XOR BX, BX
ok: MOV InPtr, BX
TEST xon, 1 (* xon/xoff enabled ? *)
JZ exit
CMP CX, XoffThreshold
JB exit
TEST XoffSent, 1
JNZ exit
MOV BX, ComBase (* send XOFF is xmit reg empty *)
LEA DX, [BX+LSR]
IN AL, DX
TEST AL, 20H
JZ exit
MOV AL, CtrlS
LEA DX, [BX+TX]
OUT DX, AL
MOV XoffSent, 1

exit:
MOV AL, 20H (* send EOI *)
OUT 20H, AL
END;
IF InCount > 0 THEN Signal( RS232Input ) END;
END;
END ComInt2;


VAR Reading :BOOLEAN;

PROCEDURE StartReading;
BEGIN
ASM
MOV BX, ComBase (* clear all 8250 registers *)
LEA DX, [BX+LSR]
IN AL, DX
LEA DX, [BX+RX]
IN AL, DX
LEA DX, [BX+MCR]
IN AL, DX

MOV BX, ComBase
LEA DX, [BX+IntEna] (* enable receiver interrupts *)
MOV AL, 5
OUT DX, AL
JMP slownow
slownow:

LEA DX, [BX+MCR] (* modem control *)
MOV AL, 0BH (* out2 + RTS + DTR *)
OUT DX, AL
JMP slowagain
slowagain:

LEA DX, [BX+RX] (* read data reg just in case... *)
IN AL, DX
END;
Reading := TRUE;
END StartReading;


PROCEDURE StopReading;
BEGIN
IF Reading THEN
ASM
MOV BX, ComBase (* disable 8250 interrupts *)
LEA DX, [BX+IntEna]
MOV AL, 0
OUT DX, AL
END;
Reading := FALSE;
XoffSent := FALSE;
END;
END StopReading;

BEGIN
Reading := FALSE;
END RS232Receiver;



PROCEDURE Init( portNumber :CARDINAL; (* 1 or 2 *)
baudRate :CARDINAL; (* 300..38400 *)
nStopBits :CARDINAL; (* 1 or 2 *)
parityEnable :BOOLEAN;
evenParity :BOOLEAN;
charSize :CARDINAL; (* 5..8 *)
inBufferSize :CARDINAL; (* input buffer size *)
VAR done :BOOLEAN (* success *)
);
VAR lcr :BITSET;
baud :CARDINAL;
BEGIN
StopReading;
IF BuffSize > 0 THEN DEALLOCATE( BuffPtr, BuffSize ) END;
IF portNumber = 1 THEN
ComBase := Com1Base;
ComIntNo := Com1IntNo;
ELSIF portNumber = 2 THEN
ComBase := Com2Base;
ComIntNo := Com2IntNo;
ELSE done := FALSE; RETURN
END;
ComPort := portNumber;
ComRX := ComBase + RX;
ComLSR := ComBase + LSR;
lcr := BITSET( charSize - 5 );
IF nStopBits > 1 THEN lcr := lcr + {2} END;
IF parityEnable THEN lcr := lcr + {3} END;
IF evenParity THEN lcr := lcr + {4} END;
IF baudRate MOD 50 = 0 THEN
baud := 2304 DIV (baudRate DIV 50);
ELSIF baudRate = 75 THEN
baud := 1536
ELSIF baudRate = 110 THEN
baud := 1047
ELSE
done := FALSE;
RETURN
END;
BuffSize := inBufferSize;
InPtr := 0;
OutPtr := 0;
InCount := 0;
IF Available( BuffSize ) THEN
ALLOCATE( BuffPtr, BuffSize )
ELSE
done := FALSE;
RETURN
END;
XoffThreshold := BuffSize DIV 4 * 3;
XonThreshold := BuffSize DIV 2;
ASM
MOV BX, ComBase
LEA DX, [BX+LCR] (* DLAB := 1 *)
MOV AL, 80H
OUT DX, AL

MOV AX, baud
LEA DX, [BX+DivL] (* set divisor *)
OUT DX, AL
JMP slow (* for PC/AT *)
slow:
INC DX
MOV AL, AH
OUT DX, AL
JMP slow2
slow2:

LEA DX, [BX+LCR] (* line control *)
MOV AL, lcr
OUT DX, AL
END;
IF (portNumber = 1) & NOT ISR1active THEN
NewProcess( ComInt1, 512, TRUE ); (* create the ISR process *)
ISR1active := TRUE;
ELSIF NOT ISR2active THEN
NewProcess( ComInt2, 512, TRUE );
ISR1active := TRUE;
END;
done := TRUE;
END Init;


PROCEDURE ResetPars( baudRate :CARDINAL; (* 300..38400 *)
nStopBits :CARDINAL; (* 1 or 2 *)
parityEnable :BOOLEAN;
evenParity :BOOLEAN;
charSize :CARDINAL; (* 5..8 *)
VAR done :BOOLEAN (* success *)
);
VAR lcr :BITSET;
baud :CARDINAL;
BEGIN
StopReading;
ComRX := ComBase + RX;
ComLSR := ComBase + LSR;
lcr := BITSET( charSize - 5 );
IF nStopBits > 1 THEN lcr := lcr + {2} END;
IF parityEnable THEN lcr := lcr + {3} END;
IF evenParity THEN lcr := lcr + {4} END;
IF baudRate MOD 50 = 0 THEN
baud := 2304 DIV (baudRate DIV 50);
ELSIF baudRate = 75 THEN
baud := 1536
ELSIF baudRate = 110 THEN
baud := 1047
ELSE
done := FALSE;
RETURN
END;
ASM
MOV BX, ComBase
LEA DX, [BX+LCR] (* DLAB := 1 *)
MOV AL, 80H
OUT DX, AL

MOV AX, baud
LEA DX, [BX+DivL] (* set divisor *)
OUT DX, AL
JMP slow (* for PC/AT *)
slow:
INC DX
MOV AL, AH
OUT DX, AL
JMP slow2
slow2:

LEA DX, [BX+LCR] (* line control *)
MOV AL, lcr
OUT DX, AL
END;
StartReading;
done := TRUE;
END ResetPars;


PROCEDURE GetCom( VAR ch :CHAR; VAR received :BOOLEAN );
BEGIN
IF InCount > 0 THEN
ch := BuffPtr^[OutPtr];
received := TRUE;
INC( OutPtr );
IF OutPtr >= BuffSize THEN OutPtr := 0 END;
ASM (* guarantee single 8086 instruction *)
DEC InCount
END;
ELSE
ch := 0C;
received := FALSE;
END;
IF XoffSent & (InCount < XonThreshold) THEN
PutCom( CtrlQ );
XoffSent := FALSE;
END;
END GetCom;


PROCEDURE PutCom( ch :CHAR );
BEGIN
ASM
MOV BX, ComBase
LEA DX, [BX+LSR]
wait: (* wait for tx buffer to empty *)
IN AL, DX
TEST AL, 20H
JZ wait
MOV AL, ch
LEA DX, [BX+TX]
OUT DX, AL
END;
END PutCom;


PROCEDURE XON;
BEGIN
xon := TRUE;
END XON;


PROCEDURE XOFF;
BEGIN
xon := FALSE;
IF XoffSent THEN PutCom( CtrlQ ); XoffSent := FALSE END;
END XOFF;


PROCEDURE Stop;
BEGIN
StopReading;
ResetVector( Com1IntNo, OldCom1Int );
ResetVector( Com2IntNo, OldCom2Int );
END Stop;


VAR p :POINTER TO CARDINAL;
ok :BOOLEAN;

BEGIN
(* get COM port addresses from BIOS *)
p.SEG := 40H; (* BIOS DATA segment *)
p.OFS := 0; Com1Base := p^;
p.OFS := 2; Com2Base := p^;

(* initialize general variables *)
XoffSent := FALSE;
BuffSize := 0;
xon := FALSE;

ISR1active := FALSE;
ISR2active := FALSE;

(* save current COM ISRs *)
GetVector( Com1IntNo, OldCom1Int );
GetVector( Com2IntNo, OldCom2Int );
TermProcedure( Stop );

(* setup process stuff *)
InitSignal( RS232Input ); (* Inititalize our signal *)

END RS232.