DEFINITION MODULE IOLink; (* Types and procedures giving the standard implementation of channels *) FROM IOChan IMPORT ChanId, DeviceErrNum, ChanExceptions; FROM IOConsts IMPORT ReadResults; FROM ChanConsts IMPORT FlagSet; FROM SYSTEM IMPORT ADDRESS; (* Devices need to identify themselves in order to allow a check to be made that device-dependent operations are applied only for channels opened to that device: *) TYPE DeviceId; (* values of this type are used to identify new device modules and are normally obtained by them during their intialization *) PROCEDURE AllocateDeviceId (VAR did : DeviceId); (* Allocates a unique value of type DeviceId and assigns this value to the parameter did *) (* a new device module open procedure obtains a channel by calling MakeChan *) PROCEDURE MakeChan ( did : DeviceId; VAR cid : ChanId); (* Attempts to make a new channel for the device module identified by did. If no more channels can be made, the identity of the bad channel is assigned to cid. Otherwise, the identity ofa new channel is assigned to cid. *) (* If a channel is allocated but the call of the device module open procedure is not successful, and on a successful call of a device module close procedure, the device module unmakes the channel and returns the value identifying the bad channel to its client: *) PROCEDURE UnMakeChan ( did : DeviceId; VAR cid : ChanId); (* If the device module identified by the parameter did is not the module that made the channel identified by the parameter cid, the exception wrongDevice is raised. Otherwise, the channel is deallocated and the value identifying the bad channel is assigned to cid. *) (* If the call of the device module open procedure is successful, the device module obtains a pointer to a device table for the channel, which will have been initialized by MakeChan. It then changes the fields of the device table to install its own values for the device data, supported operations, and flags, and returns to its client the identity of the channel. *) TYPE DeviceTablePtr = POINTER TO DeviceTable; (* Values of this type are used to refer to device tables *) (* Device modules supply procedures of the following types: *) TYPE LookProc = PROCEDURE (DeviceTablePtr, VAR CHAR, VAR ReadResults); SkipProc = PROCEDURE (DeviceTablePtr); SkipLookProc = PROCEDURE (DeviceTablePtr, VAR CHAR, VAR ReadResults); TextReadProc = PROCEDURE (DeviceTablePtr, ADDRESS, CARDINAL, VAR CARDINAL); TextWriteProc = PROCEDURE (DeviceTablePtr, ADDRESS, CARDINAL); WriteLnProc = PROCEDURE (DeviceTablePtr); RawReadProc = PROCEDURE (DeviceTablePtr, ADDRESS, CARDINAL, VAR CARDINAL); RawWriteProc = PROCEDURE (DeviceTablePtr, ADDRESS, CARDINAL); GetNameProc = PROCEDURE (DeviceTablePtr, VAR ARRAY OF CHAR); ResetProc = PROCEDURE (DeviceTablePtr); FlushProc = PROCEDURE (DeviceTablePtr); FreeProc = PROCEDURE (DeviceTablePtr); (* Carry out the operations involved in closing the corresponding channel, including flushing buffers, but do not unmake the channel. This procedure is called for each open channel at program termination. *) TYPE DeviceData = ADDRESS; DeviceTable = RECORD (* Initialized by MakeChan to: *) cd : DeviceData; (* the value NIL *) did : DeviceId; (* the value given to MakeChan *) cid : ChanId; (* the identity of the channel *) result : ReadResults; (* the value notKnown *) errNum : DeviceErrNum; (* undefined *) flags : FlagSet; (* FlagSet{} *) doLook : LookProc; (* raise exception notAvailable *) doSkip : SkipProc; (* raise exception notAvailable *) doSkipLook : SkipLookProc; (* raise exception notAvailable *) doTextRead : TextReadProc; (* raise exception notAvailable *) doTextWrite : TextWriteProc; (* raise exception notAvailable *) doLnWrite : WriteLnProc; (* raise exception notAvailable *) doRawRead : RawReadProc; (* raise exception notAvailable *) doRawWrite : RawWriteProc; (* raise exception notAvailable *) doGetName : GetNameProc; (* return the empty string *) doReset : ResetProc; (* do nothing *) doFlush : FlushProc; (* do nothing *) doFree : FreeProc; (* do nothing *) END; (* The pointer to the device table for a channel is obtained using the following procedure: *) PROCEDURE DeviceTablePtrValue (cid : ChanId; did : DeviceId): DeviceTablePtr; (* If the device module identified by the parameter did is not the module that made the channel identified by the parameter cid, the exception wrongDevice is raised. Otherwise, a pointer to the device table for the channel is returned. *) (* A device module can ask if it opened a given channel. It does this to implement a corresponding enquiry function that is exported from the device module: *) PROCEDURE IsDevice (cid : ChanId; did : DeviceId): BOOLEAN; (* Tests if the device module identified by the parameter did is the module that made the channel identified by the parameter cid. *) TYPE DevExceptionRange = ChanExceptions; (* [notAvailable .. textParseError] *) PROCEDURE RAISEdevException (cid : ChanId; did : DeviceId; x : DevExceptionRange; s : ARRAY OF CHAR); (* If the device module identified by the parameter did is not the module that made the channel identified by the parameter cid, the exception wrongDevice is raised. Otherwise the given exception is raised and the string value of the parameter s is included in the exception message. *) PROCEDURE IsIOException (): BOOLEAN; (* Returns TRUE if the current coroutine is in the exceptional execution state because of the raising of an exception from ChanExceptions Otherwise returns FALSE *) PROCEDURE IOException (): ChanExceptions; (* If the current coroutine is in the exceptional execution state because of the raising of an exception from ChanExceptions, returns the corresponding enumeration value, and otherwise raises an exception. *) END IOLink.