MODUL IQNDSK;

GLOBAL
  RDSEC,WRSEC,CRTBUF,FREBUF,
  ACTDSK,ACTTRK,ACTSEC,ACTDMA;


CONST
  FREE=255;		(* volny buffer *)
  SECSZ=128;		(* delka sektoru *)

TYPE

  TSECTOR=ARRAY[1..128] OF BYTE;
  TTRKBUF=ARRAY[1..13] OF TSECTOR;
  TPBUF=^TBUF;
  TBUF=RECORD
	NXTBUF:TPBUF;
	DSK,TRK:BYTE;
	TRKBUF:TTRKBUF;
       END;
  TPTRKBUF=^TTRKBUF;


VAR
  BUFHD,P,Q:TPBUF;
  ACTDSK,ACTTRK,ACTSEC:BYTE;
  ACTDMA:WORD;

procedure MOVE(P, Q : word; L : integer); external;

(* READ  *) function PBIORS:byte; external;
(* WRITE *) function PBIOWS:byte; external;
(* SETTRK*) procedure PBIOST(TRK : byte); external;
(* SETSEC*) procedure PBIOSS(SEC : byte); external;
(* SETDMA*) procedure PBIOSA(ADR : word); external;
(* SECTRN*) function PBIOTR(SEC : byte; TBLADR : word):integer; external;


FUNCTION MODTRK:BYTE;
(* Vypocte modifikovane cislo stopy *)

BEGIN
MODTRK:=ACTTRK*2+ORD(ODD(ACTSEC))
END;


FUNCTION MODSEC:BYTE;
(* Vypocte modifikovanee cislo sektoru *)

BEGIN
MODSEC:=(ACTSEC+1)DIV 2
END;


PROCEDURE FREBUF;
(* Oznaci vsechny buffery jako volne *)

BEGIN
P:=BUFHD;
REPEAT
  P^.DSK:=FREE;
  P:=P^.NXTBUF
UNTIL P=NIL;
END;


DYNAMIC PROCEDURE CRTBUF;
(* Alokuje maximalni pocet bufferu *)

VAR C:CHAR;
BEGIN
BUFHD:=NIL;
REPEAT
  P:=BUFHD;
  NEW(BUFHD);
  BUFHD^.NXTBUF:=P;
UNTIL (REF(C)-(BUFHD TYPE INTEGER+SIZE(TBUF)))
	< 
(NIL+SIZE(TBUF)+256);
FREBUF;
END;


FUNCTION WRSEC:BYTE;
(* Zapis sektoru na disketu a pripadne do bufferu *)

LABEL 9;

BEGIN
P:=BUFHD;
REPEAT
  IF (P^.DSK=ACTDSK) AND (P^.TRK=MODTRK) THEN
    BEGIN
    MOVE(REF(P^.TRKBUF[MODSEC]),ACTDMA,SECSZ);
    GOTO 9
    END;
  P:=P^.NXTBUF;
UNTIL P=NIL;
9:
PBIOST(ACTTRK);
PBIOSS(ACTSEC);
PBIOSA(ACTDMA);
WRSEC:=PBIOWS;
END;


FUNCTION RDSEC:BYTE;
(* Cteni sektoru *)

LABEL 1,2,9,99;
VAR RES,RES1:BYTE;

  PROCEDURE RDTRK;
  VAR STATUS,I:BYTE;
  (* cteni pulky stopy ob jeden sektor *)
  BEGIN
  I:=1; IF NOT ODD(ACTSEC)THEN I:=2;
  RES:=0; RES1:=0;
  REPEAT
    PBIOST(ACTTRK);
    PBIOSA(REF(Q^.TRKBUF[(I+1)DIV 2])); PBIOSS(I);
    STATUS:=PBIORS;
    IF STATUS<>0 THEN
      BEGIN
      RES1:=STATUS;	(* chybny alespon jeden sektor *)
      IF I=ACTSEC THEN RES:=STATUS; (* chybny prave cteny sektor *)
      END;
    I:=I+2;
  UNTIL I>26;
  END;

BEGIN
RDSEC:=0;
IF (BUFHD^.DSK=ACTDSK)AND(BUFHD^.TRK=MODTRK) THEN
  GOTO 9;	(* buffer je na zacatku fronty *)
Q:=BUFHD;
1:
P:=Q; Q:=Q^.NXTBUF;	(* dalsi buffer *)
IF (Q^.DSK=ACTDSK)AND(Q^.TRK=MODTRK) THEN
  GOTO 2;		(* buffer nalezen *)
IF Q^.NXTBUF<>NIL THEN GOTO 1;
RDTRK;			(* prepsan posledni buffer fronty *)
IF RES1<>0 THEN
  BEGIN			(* alespon jeden vadny sektor *)
  Q^.DSK:=FREE;		(* stopa se neuklada *)
  RDSEC:=RES;		(* vysledek cteni pozadovaneho sektoru *)
  MOVE(ACTDMA,REF(Q^.TRKBUF[MODSEC]),SECSZ);
  GOTO 99
  END;
Q^.DSK:=ACTDSK; Q^.TRK:=MODTRK; (* doplneni cisla disku a stopy *)
2: (* presunuti vybraneho bufferu na zacatek fronty *)
P^.NXTBUF:=Q^.NXTBUF; Q^.NXTBUF:=BUFHD; BUFHD:=Q;
9: (* cteni sektoru z prvniho bufferu *)
MOVE(ACTDMA,REF(BUFHD^.TRKBUF[MODSEC]),SECSZ);
99:
END;

END.