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15.13 XAcc

The XAcc protocol was originally designed for non-multitasking versions of GEM to allow data exchange between the main application and any number of accessories. Since the AES did not provide a function to find the application IDs (apIDs) of other applications without knowing their names, XAcc had to rely on the undocumented feature that the main application always has the apID 0. Therefore XAcc in its present (1) form does not work in a multitasking environment. However, AES 4.0 provides the new function appl_search, which allows any application to find the apIDs of all other applications running concurrently. This makes it possible to design a modified XAcc that does not use any 'dirty tricks'. This document contains a proposal for such a modified XAcc; the changes with respect to the previous definition are small and modifying an existing XAcc-based application should be a matter of minutes. Since single-tasking TOS will still be with us for a while, applications are encouraged to implement both 'traditional' and 'modern' XAcc, depending on the version number of the AES.

15.13.1 Purpose of XAcc

The GEM AES functions appl_write and appl_read can be used to exchange data between GEM applications running concurrently. In practice however, some problems need to be solved to make good use of these two functions:

The communications protocol described in this document solves all these problems. It was designed for two distinct purposes:

A potential problem caused by this protocol should be mentioned at this point: for single-tasking GEM versions, it relies on the currently undocumented fact that the main application's apID is always zero. Without this assumption there is no way to exchange data without using appl_find. Although this fact is not documented, it holds for all single-tasking versions of GEM in existence until now, both for MS-DOS and the Atari ST (this information was confirmed by Digital Research Germany). Of course the main application's apID may be different in future versions, although there is no reason to change the current behaviour for single-tasking systems. For AES 4.0 (and later) the above assumption is not needed anyway, so no compatibility problems are to be expected in the future.

A further requirement is that all programs not using this protocol must ignore its messages. This should not be a serious problem, as all GEM applications should ignore messages they do not understand. At the time of writing no programs are known to violate this rule.

15.13.2 Classic XAcc

The "classic" XAcc protocoll was finally defined on November 28, 1992. All known XAcc applications implement the protocol this way. XAcc message groups

[Note: The "levels" used in previous XAcc versions have been replaced by this new concept. Compatibility issues are discussed in a special section at the end of this document.]

Both main applications and accessories can have widely different needs for communication with other programs. Therefore XAcc defines several groups of related messages (1) that deal with a certain range of data types. The message groups always indicate the messages understood by a program, not the messages it might send to other ones. If a program supports a certain message group, it must correctly respond to all corresponding messages, whether it can actually use the supplied data or not.

In addition to XAcc message groups, there are the so-called "basic messages", which must be supported by any XAcc-aware program, and program-specific so-called "special messages".

The basic messages deal solely with identification, but no real data exchange. They are already sufficient for programs that either do not exchange data with others at all or use only special messages to communicate with a number of other specific programs.

Message group 1 specifies the exchange of ASCII-format character data.
Message group 2 deals with the exchange of drawings and pictures using the GEM metafile format and the GEM bit-image file format.

Future extensions might include sound or spreadsheet data. In addition, a message group could be defined to handle command interchange between applications, e.g. for a "Drag&Drop" protocol (2). XAcc messages

There are two kinds of XAcc messages: standard messages, which must be understood by every participating program, and special messages intended for communications between specific program combinations. The standard messages have numbers ranging from 0x400 to 0x7ff, special messages start from 0x800. The latter ones may only be sent after the receiver has been identified and is known to understand them. The following description is only concerned with standard messages. In addition to XAcc standard messages, the AES messages normally sent by the screen manager may be used. The most useful ones are AC_OPEN and MN_SELECTED; the latter one requires a knowledge of the receiver and therefore belongs to the special messages. Basic XAcc messages
ACC_ID    = 0x400
ACC_OPEN  = 0x401
ACC_CLOSE = 0x402
ACC_ACC   = 0x403
ACC_EXIT  = 0x404

These messages provide XAcc initialization and organization. This is the only part of XAcc which has to be implemented in a different way for single- and multi-tasking GEM versions. Note that the procedure described for 'multitasking' actually only depends on the existence of appl_search and hence on an AES version number >= 4.0. If some future single-tasking AES supports appl_search, the 'multitasking' initialization should be used. Multitasking AES versions with a version number < 4.0 should never exist; to be on the safe side, applications should not attempt to use XAcc if such a situation is detected (1). Single-tasking GEM versions

The communication between the main application and the accessories is initiated in the following way:

  1. When a main application is started (or terminated), all desk accessories receive an AC_CLOSE message from the AES screen manager. In response they must send an identification to the main application according to the following format:

         msg[0]:  ACC_ID (0x400)
         msg[1]:  sender's apID
         msg[2]:  length of the message - 16, giving 0
         msg[3]:  program version number and message groups
         msg[4] and msg[5]:   pointer to sender's name
         msg[6]:  menu number (menu_id) as returned by menu_register
         msg[7]:  reserved (see ACC_ACC)

    The low byte of msg[3] contains a bitmap indicating which message groups are understood by the sender. Bit zero is set for message group 1, bit one for message group 2, and so on. This is independent of the message types which the sender might itself send to others. The sender of a message must ensure that it is understood by the receiver. The high byte is used to indicate a program version number using an arbitrary encoding scheme.
    The pointer to the sender's name is stored in a machine-dependent format. The name itself is a character string following C conventions, i.e. a string of characters terminated by a zero byte. To avoid name conflicts, long names are preferred to short abbreviations. The name must be available at the given address at any time, it may not be removed after initialization. As the version number is stored in msg[3], it should not occur again in the name. (1)
    Accessories using more than one menu entry must issue one ACC_ID message for each entry used. Accessories without a menu entry must use a number of -1.
    Since msg[1] and msg[2] have the same meaning for all message types, they are no longer mentioned from now on.

  2. In response to an ACC_ID message the main application sends an identification back to the accessory. The format is identical, except that there is no menu number and thus msg[6] can be used for any other purpose if neccessary. The same applies to msg[7].

  3. In addition to the ACC_ID message, the main application informs all previously registered accessories about the new one by sending them the message

         msg[0]:  ACC_ACC (0x403)
         msg[3]:  program version number and message groups
         msg[4] and msg[5]:   pointer to accessory's name
         msg[6]:  accessory's menu number (menu_id)
         msg[7]:  accessory's apID

  4. A desk accessory receiving the ACC_ACC message from the main application sends an ACC_ID message to the thereby registered accessory, identical to the one previously sent to the main application.

  5. When an accessory is activated by receiving an AC_OPEN message, it sends the following message to the main application:
    msg[0]: ACC_OPEN
    Just before the accessory returns control to another program, it sends the message
    msg[0]: ACC_CLOSE
    When receiving ACC_OPEN, the main application restores all system variables it has changed to their original values (if possible and neccessary). After receiving ACC_CLOSE, it may set them again to any desired value.
    Accessories should change system variables only after sending ACC_OPEN and restore them before ACC_CLOSE.
    There have been some problems with the implementation of ACC_OPEN and ACC_CLOSE that should be mentioned. The system was designed with window-less accessories in mind, i.e. accessories that only display a dialog box. For these accessories, the above procedure is well-defined. Accessories that use windows however have no way to find out if they have been activated or deactivated, because they do not receive a message to indicate this (starting from AES 4.0, this problem is solved). Therefore such accessories must be careful with ACC_OPEN and ACC_CLOSE. The most important thing is to guarantee that ACC_OPEN and ACC_CLOSE always occur in pairs, and that in between no other program gains control. How exactly this is implemented depends on the specific application. Sometimes the best implementation is not to use ACC_OPEN and ACC_CLOSE at all.

After initialization is completed, all participating programs know the identity of all other ones, either by receiving an ACC_ID message or by receiving an ACC_ACC message. The main application is always informed about accessory activities. If in addition it proves neccessary to inform one accessory about the activation of another one, this can be accomplished by sending special messages (starting from 0x800). Multitasking GEM versions

The initialization procedure is much simpler in this case. Any application, i.e. both 'standard' applications and accessories, uses appl_search to detect all currently running AES processes when it is started. To each application or accessory (i.e. everything but system processes) it sends an ACC_ID message:

  msg[0]:  ACC_ID (0x400)
  msg[1]:  sender's apID
  msg[2]:  length of the message - 16, giving 0
  msg[3]:  program version number and message groups
  msg[4] and msg[5]:  pointer to sender's name
  msg[6]:  menu number (menu_id) as returned by menu_register
  msg[7]:  reserved

The low byte of msg[3] contains a bitmap indicating which message groups are understood by the sender. Bit zero is set for message group 1, bit one for message group 2, and so on. This is independent of the message types which the sender might itself send to others. The sender of a message must ensure that it is understood by the receiver. The high byte is used to indicate a program version number using an arbitrary encoding scheme.

The pointer to the sender's name is stored in a processor-dependent format. The name itself is a string of characters terminated by two zero bytes. To avoid name conflicts, long names are preferred to short abbreviations. The name must be available at the given address at any time, it may not be removed after initialization. It must also reside in globally accessible memory. As the version number is stored in msg[3], it should not occur again in the name. (1)

Applications using more than one menu entry must issue one ACC_ID message for each entry used. Accessories without a menu entry must use a number of -1.

When receiving an ACC_ID message, an application replies by sending a message of the same format to the original sender, the only difference being that ACC_ACC is used instead of ACC_ID. Applications with several menu entries must again send one message for each entry.

The messages ACC_OPEN and ACC_CLOSE are not used in multitasking systems.

Note: The only difference between ACC_ID and ACC_ACC for multitasking systems is that an application receiving ACC_ID sends ACC_ACC as a reply, whereas no reply is sent on receiving ACC_ACC. This prevents applications from sending ACC_ID to each other indefinitely. Obviously the name ACC_ACC has lost its original meaning and probably should be changed. But since the symbolic names do not influence the actual behaviour of any program, this is not really important at all.

Since in a multitasking environment every participating application can terminate, some means must be provided to tell other applications about this. Therefore the message ACC_EXIT has been added to the list of level 0 messages. Before terminating, any application sends

  msg[0]:  ACC_EXIT (0x404)
  msg[1]:  sender's apID
  msg[2]:  length of the message - 16, giving 0

to all applications that have ever registered themselves by sending ACC_ID or ACC_ACC. Extended names

Experience with XAcc has shown that it would often be useful to have more information about an application than specified with ACC_ID messages. For example it is sometimes useful to check for a special feature that is not unique to a single program, but to several similar ones. This was the motivation for the introduction of "extended names".

An "extended name" is a character string of the format:


i.e. a "standard" name followed by the string "XDSC" (for "eXtended DeSCription"), followed by a list of strings containing additional information. The end of the list is marked by an additional zero byte.

Each information string indicates by its first byte what kind of information it contains. Currently the following types are defined:

'1' - application type (human-readable)
The text following this byte (an ASCII-1, 0x31) should roughly specify the type of application, e.g. "word processor" or "spreadsheet". The purpose is for applications to present this information to the user to let him/her decide where data should go. This is not the place for advertising hype; a word processor should call itself "word processor" and not "document editing and design system".
It should be clear that the text should be understandable for end users, especially it should be in the language used for the user interface.
'2' - application type (machine-readable)
Currently defined are:
"WP" - Word processor
"DP" - DTP
"ED" - Text editor
"DB" - Database
"SS" - Spreadsheet
"RG" - Raster graphics application
"VG" - Vector graphics application
"GG" - General graphics application
"MU" - Music application
"CD" - CAD
"DC" - Data communication
"DT" - Desktop
"PE" - Programming environment
'X' - extended features This string is used to indicate special communication capabilities of an application. It can be used to give more specific information than just the message groups understood. Since this information is meant to be used by other applications rather than end users, short abbreviations are sufficient.
'N' - generic name Often several related, but not completely identical, applications have different names. Marketing requirements may even dictate changes of the "official" brand names, making them unsuitable for a "technical" identification. In such cases a "generic" name for all these programs can be specified, which is mainly used by other programs wishing to use special messages.

The "normal" name should be the "official" name of the program, just as it is used on the package, in the manual, and in similar places. It should be presentable to the user to let him/her decide where to send data.

Example: The address database "That's Address" identifies itself with the extended name (in C syntax)

"That's Address\0XDSC\01database\02DB\0XMM\0XSU\0",

indicating that it is a database with features "MM" and "SU". The first one indicates a special mail merge mode, the second one the possibility of retrieving data by sending the key via ACC_TEXT. (Further information on this program can be obtained from its manual.) Message group 1
ACC_ACK  = 0x500
ACC_TEXT = 0x501
ACC_KEY  = 0x502
  1. Transmitting text data:

         msg[0]:  ACC_TEXT (0x501)
         msg[4] and msg[5]:   pointer to text

    The text may contain all printable ASCII characters (code >= 32) and the following control codes:
    0x09 TAB (may be interpreted as a space by the receiver)
    0x0A LF (usually ignored by receiver)
    0x0D CR (used to mark an end-of-line (or end-of paragraph)
    Other control codes may only be used if the receiver is known to understand them. The text is terminated by a zero byte. After the text has been interpreted completely, the receiver acknowledges by sending
         msg[0]:  ACC_ACK (0x500)
         msg[3]:  0 if the text was simply ignored
                  1 if it was used in some sensible way

    The sender of a text message may not change the text nor send any other text messages to the same receiver until is has received the acknowledgement.
    The sender must make sure that the memory used to store the text is globally accessible.
    The receiver should normally interpret the text as if it were typed from the keyboard. A word processor would for example insert it into the currently edited document (this implies using CR as an end-of- paragraph mark), a command line interpreter would interpret the text as a command (which implies using CR as an end-of-line mark).

  2. Simulation of a key press:

         msg[0]:  ACC_KEY (0x502)
         msg[3]:  scancode of the simulated key and corresponding
                  ASCII-code (as returned by evnt_keybd)
         msg[4]:  state of the SHIFT keys (as returned by Kbshift)

    This message should be regarded identical to a keyboard event(1). It can be used to send control commands to a receiver which might have been issued from the keyboard. Of course this requires a knowledge of the receiver, as no standard keyboard command sets exist. It should be noted that the receiver is free to use only the ASCII-code or only the scan code, or both of them.
    This message is acknowledged after its interpretation with:
         msg[0]:  ACC_ACK (0x500)
         msg[3]:  0 if ACC_KEY was ignored or a given command was not
                  understood, 1 if some action was taken.

To prevent a deadlock if a program does not properly acknowledge a message, the sender should have some way to recover. An accessory could for example stop waiting for an acknowledgement after the next AC_OPEN, a main application might time out after a sufficiently long period. Message group 2
ACC_META = 0x503
ACC_IMG  = 0x504

These message are used to exchange drawings and pictures. Only the file formats defined in the GEM documentation are used; they are sufficient to meet most requirements, and any GEM application should be able to handle them anyway.

  1. Sending a metafile:

         msg[0]:  ACC_META (0x503)
         msg[3]:  1 for the final part, 0 otherwise
         msg[4] and msg[5]:   pointer to data
         msg[6] and msg[7]:   length of data (32 bit longword)

    The metafile data is sent in the same format as it would be stored on disk. As metafiles can become quite large, and often accessories in particular do not have sufficient memory free to store them, a file can be sent in several pieces. The receiver has to take care of assembling all parts to restore the original data, if neccessary by writing the parts to a file. The last part of a file is marked by msg[3]=1. The sender may send no other data between the parts of a file. msg[6] and msg[7] contain the length of the part being sent, not the total length.
    The receiver acknowledges each part as described for group 1. As for text messages, the sender must make sure that the data to be transferred is stored in globally accessible memory.

  2. Sending a bit image file:
    msg[0]: ACC_IMG (0x504)
    otherwise identical to 1. Compatibility considerations

There are two major changes with respect to the original(1) XAcc definition:

  1. "Levels" have been replaced by "message groups"
    The motivation for this change was that the classification according to exchangeable data types was not really a hierarchical one; there is no reason why a programm accepting graphics should also be able to understand text. The new scheme makes no such arbitrary assumptions.
    There is only one situation in which a possible incompatibility could occur: an application following the "old" convention encounters a "new" application and one of them indicates 2 in the level/message group byte. This would be interprets as "graphics only" by one and as "graphics and text" by the other. Since the number of level-2 applications was always extremely small (in fact, the author(2) knows only of a single one), this should be no problem in practice.

  2. Extended names have been introduced
    This could lead to a problem in the extremely unlikely case of an "old" application using a name string which is accidentally followed by "XDSC".

In any case it is expected that most applications will be converted to the new rules soon, if only to support MultiTOS.

15.13.3 Extended XAcc

This chapter describes developments of the XAcc protocol after "Classic XAcc" (11/28/92). Last changes have been made on June 15, 1995.

Seit der letzten offiziellen Dokumentationen zum XAcc-Protokoll haben sich einige Erweiterungen ergeben, die nun zusammengefaßt worden sind. Einige der Erweiterungen sind aus speziellen Formen des Datenaustauschs zwischen der Textverarbeitung That's Write und der Adreßverwaltung That's Address bzw. dessen Nachfolger no|Address hervorgegangen. Trotzdem sind diese Erweiterungen auch beliebigen anderen Applikationen zugänglich und die Verwendung dieser Applikationsnamen in der folgenden Dokumentation hat nur beispielhaften Charakter (That's Address = TA und That's Write = TW). Bei den Erweiterungen handelt es sich um: MailMerge-Protokoll

Dieses Protokoll arbeitet aus historischen Gründen mit ACC_TEXT- Messages. Das TW schickt dem TA zuerst eine ACC_TEXT -Messages mit einem String, der mit "#I" beginnt und nach dem 'I' den SDF- Formatstring beinhaltet, der dem TA sagt, welche Teile eines Adreßdatensatzes übertragen werden sollen.

Beispiel: "#IA1,A2,A3,A4,T1" (die ersten 4 Adreßfelder und die 1. Telefonnr.).

Bei erfolgreichem Empfang dieser Nachricht wird dem TW eine ACC_TEXT- Message mit dem String "0" zurückgesendet, ansonsten ein Leerstring ".

Nun kann TW beginnen, die einzelnen Adreßdaten mittels der ACC_TEXT- Message "#N" anzufordern. Bei Empfang einer solchen Nachricht schickt TA für jedes Adreßfeld einer Adresse eine ACC_TEXT-Message und zum Abschluß eines Datensatzes einen Leerstring ". Remote-Mailmerge-Protokoll

Für dieses Protokoll gibt es zwei neue XAcc-message Typen, nämlich:

#define ACC_FORCESDF        0x520
#define ACC_GETSDF          0x521

TA sendet dem TW ein ACC_FORCESDF, wenn eine Adresse oder eine Adreßliste an das TW geschickt werden soll. Im Falle, daß es sich nur um eine Adresse handelt, steht in msg[4]+[5] ein Pointer auf das Suchwort der Adresse, bei einer Adreßliste steht in msg[4]+[5] ein Pointer auf "#L". Die ACC_FORCESDF-message muß mit einem ACC_ACK bestätigt werden (msg[3]==1 -> OK und msg[3]==0 -> ERROR).

Wenn TW ein "#L" bekommst, dann fährt TW ein ganz normales MailMerge- Protokoll (eingangs erklärt). Wenn TW ein Suchwort bekommt (max. 20 Zeichen lang), dann fordert TW beim TA diese Adresse mittels ACC_GETSDF an. Die ACC_GETSDF-message muß in msg[4]+[5] einen Pointer auf einen Buffer haben, in dem zuerst das Suchwort mit abschließendem '\0' steht und dann der XDF-Formatstring steht (Bsp.: "JÖRG\0A1,A2,A3\0").

Wenn TA die ACC_GETSDF-message verstehen kann, dann schickt es ein ACC_ACK mit msg[3]==1, ansonsten ein ACC_ACK mit msg[3]==0. Anschließend bekommt TW die Daten dieser einen Adresse wie beim normalen MailMerge- Protokoll.

TW muß in seinem XDSC-String ein "XRM" zu stehen haben, damit TA von sich aus ein Remote-Mailmerge-Protokoll startet.

TA hat jetzt folgende XDSC-Features (Bsp. ACC):

const char ta2Ident[] = "That's Address ACC\0XDSC\0"
                        "XMM\0XSU\0XDI\0XRM\0NnoAddress ACC\0";
XMM MailMerge
XSU Suchwortübergabe (optional mit anschließendem '?')
XDI Inquiry-Protokoll
XRM Remote-MailMerge Inquiry-Protokoll

Im Prinzip läuft das ganze Inquiry-Protokoll in 2 Stufen ab. Zuerst werden die Daten der verfügbaren Datenbanken ermittelt, und anschließend (zeitlich voneinander völlig unabhängig) werden die einzelnen Felder einer ausgewählten Datenbank erfragt.

Also Part 1 (am Beispiel von TA und TW):

            TA                  |                   TW





    }   /* <n> mal, wobei <n> bei ACC_DSINFO übertragen wurde */

Erklärung der einzelnen Protokollelemente:

Hiermit wird das Inquiry-Protokoll initiiert. Diese Message enthält einen Pointer auf eine Variable des Typs Xacc_Dsi_Request, in dem codiert wird, welche Felder welchen Typs gewünscht sind.
        msg[0]            = ACC_GETDSI (0x510)
        msg[1]            = application id
        msg[4] und msg[5] = Pointer auf die gewünschten Feld-Typen
                            (siehe XACC.H)
Auf ein ACC_GETDSI antwortet die angefragte Applikation mit dieser Message. Hierbei wird ein Pointer auf eine Variable des Typs Xacc_Dsinfo, wenn die Anfrage beantwortet werden kann, oder ein NULL-Pointer, wenn die Anfrage nicht beantwortet werden kann, der anfragenden Applikation übergeben.
        msg[0]            = ACC_DSINFO (0x511)
        msg[4] und msg[5] = Pointer auf Xacc_Dsinfo Struktur
                            (siehe XACC.H) oder NULL

Die anfragende Applikation beantwortet alle Replys seinerseits mit einer ACC_ACK= Message: ACC_ACK:
        msg[0]            = ACC_ACK
        msg[3]            = 1     wenn alles OK ist
                          = 0     wenn ein Fehler aufgetreten ist
                                  (Abbruch des Protokolls)
Wenn die ACC_DSINFO Message von der anfragenden Applikation bestätigt wurde, so wird für jede verfügbare Datei eine ACC_FILEINFO-Message mit einem Pointer auf eine Variable des Typs Xacc_File_Info, oder ein NULL-Pointer bei einem Fehler, an die anfragende Applikation gesendet.
Jede dieser Messages muß, wie oben erwähnt, mit einer ACC_ACK von der anfragenden Applikation bestätigt werden.
        msg[0]            = ACC_FILEINFO (0x512)
        msg[4] und msg[5] = Pointer auf Xacc_File_Info Struktur
                            (siehe XACC.H) oder NULL

Wenn dieser erste Teil des Inquiry-Protokolls erfolgreich beendet wurde, dann kann die anfragende Applikation dem Anwender die Liste der verfügbaren Datenbanken und deren Information 'auf die Nase knallen' und ihn eine Auswahl treffen lassen.

Tut der Anwender dies, so läuft der 2. Part des Inquiry-Protokolls los (wieder am Beispiel von TA und TW):

            TA                  |                   TW



    }   /* <n> mal, wobei <n> bei ACC_FILEINFO übertragen wurde */

Erklärung der einzelnen Protokollelemente:

Hiermit wird von der anfragenden Applikation eine Datenbank ausgewählt (die entsprechende Datenbank-ID hat sie ja bei der ACC_FILEINFO Message in der Struktur Xacc_File_Info empfangen) und gibt der angefragten Applikation bekannt, daß nun die einzelnen Feldinformationen übertragen werden sollen.
        msg[0]            = ACC_GETFIELDS (0x513)
        msg[1]            = application id
        msg[3]            = ID der gewünschte Datenbank
Wenn die ACC_GETFIELDS Message von der anfragenden Applikation bestätigt wurde, so wird für jedes Feld eine ACC_FIELDINFO Message mit einem Pointer auf eine Variable des Typs Xacc_Field_Info, oder ein NULL-Pointer bei einem Fehler, an die anfragende Applikation gesendet.
Jede dieser Messages muß, wie oben erwähnt, mit einer ACC_ACK von der anfragenden Applikation bestätigt werden.
        msg[0]            = ACC_FIELDINFO (0x514)
        msg[4] und msg[5] = Pointer auf Xacc_Field_Info Struktur
                            (siehe XACC.H) oder NULL

In That's / no| Address wurden im Moment die Feldtypen FT_CHAR, FT_DATE und FT_TIME implementiert. Request/Reply-Protokoll

Es werden zwei weitere Message-Typen eingeführt, um einen allgemeinen Datenaustausch zu ermöglichen:

#define ACC_REQUEST     0x480
#define ACC_REPLY       0x481
Mittels dieser Nachricht fordert man bei einer anderen Applikation einen Dienst an. Der Aufbau dieser Nachricht ist folgendermaßen:
      msg[0]:     ACC_REQUEST (0x480)
      msg[1]:     Application-ID des Senders
      msg[2]:     0
      msg[3]:     Das high-Byte ist frei für Applikationsspezifische
                  Informationen und im low-Byte ist der Typ der
                  Daten codiert, die mit dieser Nachricht verschickt
                  0x01  String, d.h. msg[4]+msg[5] ist
                        ein Pointer auf den String
                  0x02  Env-String, d.h
                        msg[4]+msg[5] ist ein Pointer
                        auf den Env-String (mehrere durch
                        '\0' getrennte Strings mit
                        abschließenden doppelten '\0'-Bytes)
                  0x03  binär-Daten, d.h.
                        msg[4]+msg[5] ist ein Pointer auf
                        die binär-Daten. In diesem Fall muß der
                        Empfänger natürlich über die Struktur
                        Bescheid wissen! (lokale Typunterscheidung
                        ist z.B. mittels des high-Bytes möglich)
                  0x04  code, d.h. msg[4] bis msg[7]
                        enthalten direkt die Daten (sinnvoll bei
                        Übertragung von Datenmengen bis 8 Byte)
      msg[4,5]:   Pointer auf die Daten (außer Typ 0x04)
      msg[6,7]:   Länge des Datenbereichs incl. eventueller
                  '\0'-Bytes (außer Typ 0x04)

Es existieren zwei verschiedene Möglichkeiten, diese Nachricht zu beantworten:
  • ACC_ACK mit msg[3]=0, wenn die empfangende Applikation diese Nachricht nicht bearbeiten kann

  • ACC_REPLY, wenn die Nachricht bearbeitet werden konnte und eine Antwort zurückgeschickt wird

Mittels dieser Nachricht wird eine ACC_REQUEST Anforderung erfolgreich beantwortet. Der Aufbau dieser Nachricht ist folgendermaßen:
            msg[0]:     ACC_REPLY (0x481)
                .       siehe ACC_REQUEST!

Applikationen, die oben beschriebene Protokollelemente unterstützen, müssen in ihrer XDSC-Beschreibung das Extended-Feature "RQ" enthalten haben.

15.13.4 Example: no|Link's XAcc protocol

Das no|Link-Accessory wurde für die Ansteuerung von Infrarotgeräten konzipiert und beinhaltet eine XAcc-Kommunikationsschicht für die Ansteuerung durch spezielle Applikationen. Zum momentanen Zeitpunkt wird das Media-Link-Interface von Catch Computer unterstützt. Eine weitere Anpassung an das no|Remote-Interface von no|Software ist in Arbeit.

Das no|Link-Accessory verwaltet alle Informationen, die zur Ansteuerung der verwendeten Infrarot- oder sonstiger Hardware benötigt werden. Jedem hardwareabhängigen Code (z.B einem Infrarotsignal) wird ein Befehl zugeordnet, und für jedes Gerät (z.B. Videorekorder) existiert eine Liste solcher Befehle.

Will nun z.B. eine Applikation für die Fernbedienung eines Videorekorders ein Infrarotsignal für die Play-Taste senden, so schickt es no|Link eine XAcc-Nachricht, in der das Kommando <senden>, das Gerät <VIDEOREKORDER> und der Befehl <PLAY> codiert sind.

Damit eine Applikation mit no|Link vollständig kommunizieren kann, muß diese das Request/Reply-Protokoll unterstützen, was als Extended- Feature in der XDSC-Beschreibung durch ein "RQ" bekannt gemacht wird. Nur so ist es möglich, die Liste der eingetragenen Geräte von no|Link erhalten zu können.

Wenn die Applikation auch Codes vom Accessory empfangen können will (nur mit entsprechender Hardware möglich), so muß als Extended-Feature in der XDSC-Beschreibung zusätzlich ein "RR" (Remote Receive) enthalten sein. Alle Applikationen, die mit noLink arbeiten wollen, müssen den XAcc-Level 1 unterstützen.

Als Application-Type enthält das no|Link-Accessory im XDSC "\2RC" (Remote Control).

Die vollständige XAcc-Identifikation von no|Link lautet zur Zeit folgendermaßen (in C-Syntax):

    char xaccNoLinkIdent[] =    "Infrarot Manager\0"

Eine denkbare XAcc-Identifikation für eine no|Link-Applikation könnte so aussehen:

    char xaccIdentstring[] =    "VideoControl\0"
                                "1Video Fernbedienung\0"
                                "Nno|Video ACC\0";

Die Kommunikation zwischen Applikation und dem no|Link-Accessory findet hauptsächlich über ACC_TEXT Messages statt.

Das Accessory versteht zur Zeit folgende Befehle, die als String mittels einer ACC_TEXT Message versendet werden müssen (<X> := <Gerät>:<Befehl>):

"S <X>" Senden eines Befehls, z.B: "S VIDEO:PLAY".
"P <X>" Präparieren eines Befehls, z.B: "P VIDEO:PLAY". Hierbei wird der Infrarot-Hardware der Code für diesen Befehl mitgeteilt, aber noch nicht abgeschickt.
"S" Senden des zuletzt präparierten Befehls.
"T <X>" Test der Existenz eines Befehls.
Insbesondere bei der Neuinstallation einer Fernsteuerungs- Applikation sollten alle Geräte und Befehle, die diese Applikation verwendet, dem Accessory mitgeteilt werden!
Wenn no|Link den mitgelieferten Befehl nicht kennt, so wird der Benutzer aufgefordert, die nötige "Lernprozedur" zu tätigen bzw. dem neuen Befehl einen schon vorhandenen zuzuweisen.
Es sollte in jeder Fernsteuerungsapplikation eine Funktion geben, die es dem Benutzer ermöglicht, alle unterstützten Befehle zu "testen" - am besten über einen "Anmelden"-Button.

Die Testfunktion ist die einzige, die u.U. eine Interaktion mit dem Benutzer führt. Alle anderen vollführen keine Ausgabe.

Als Antwort erhält die Applikation eine ACC_ACK-Message, bei der in msg[3] der Erfolg der Behandlung des Befehls vermerkt ist:

1 Operation war erfolgreich
0 Gerät/Befehl ist nicht vorhanden bzw. Fehler bei der Bearbeitung

Geräte- und Befehlsnamen dürfen maximal 32 Zeichen lang sein und dürfen KEINEN ':' enthalten. Es wird nicht zwischen Groß- und Kleinschreibung unterschieden.

Eine Applikation kann vom Accessory eine Liste der eingetragenen Geräte anfordern. Hierfür muß die Applikation das neue XAcc- Request/Reply-Protokoll verstehen (siehe oben bzw. XACC.H).

Um die Liste anzufordern, wird von der Applikation ein ACC_REQUEST an das Accessory geschickt, wobei diese Nachricht folgendermaßen aufgebaut sein muß:

    msg[0] = ACC_REQUEST (0x480)
    msg[1] = apid
    msg[2] = 0
    msg[3] = 0x04       /* Datentyp: Code */
    msg[4] = 'D'        /* 'D' steht für "devices" */
    msg[5] = 0
    msg[6] = 0
    msg[7] = 0

Als Antwort erhält die Applikation, wenn ein Fehler auftrat eine ACC_ACK- Message mit msg[3] == 0, oder bei Erfolg eine ACC_REPLY- Message:

    msg[0] = ACC_REPLY (0x481)
    msg[1] = apid von no|Link
    msg[2] = 0
    msg[3] = 0x02       /* Datentyp: Environment-String */
    msg[4]+msg[5] = Pointer auf einen global zugreifbaren
                    Speicher, in dem die Liste der Geräte
                    in folgendem Format steht:
    msg[6]+msg[7] = long-value, der die Größe des Buffers
                    angibt (inkl. der abschließenden zwei

Der Empfang einer ACC_REPLY-Message muß abschließend mit einer ACC_ACK- Message bestätigt werden, damit das no|Link-Accessory seine Resourcen wieder freigeben kann!

15.13.5 XACC.H

/*                                                                  */
/*                XAcc definitions (PureC syntax)                   */
/*                                                                  */

#ifndef __XACC__
# define __XACC__

    XAcc message types
/* Level 0 */
# define ACC_ID             0x400
# define ACC_OPEN           0x401
# define ACC_CLOSE          0x402
# define ACC_ACC            0x403
# define ACC_EXIT           0x404

/* Level 1 */
# define ACC_ACK            0x500
# define ACC_TEXT           0x501
# define ACC_KEY            0x502

/* Level 2 */
# define ACC_META           0x503
# define ACC_IMG            0x504

 * extended XACC Message-Types:
 * Diese Messages sind relativ "unabhängig" vom XACC-Level der
 * Applikationen, d.h. sie sollten nur verwendet werden,
 * wenn der Kommunikationspartner in seiner XDSC-Beschreibung
 * über das ensprechende Extended-Feature verfügt!

/* Reuest/Reply Protokoll: (Extended-Feature "RQ")      */
/*        ACC_ACK Messages sind Teil des Protokolls und */
/*        müssen deshalb verstanden werden!             */
# define ACC_REQUEST        0x480
# define ACC_REPLY          0x481

/* Inquiry Protokoll: (Extended-Feature "DI")           */
/*        ACC_ACK Messages sind Teil des Protokolls und */
/*        müssen deshalb verstanden werden!             */
#define ACC_GETDSI          0x510
#define ACC_DSINFO          0x511
#define ACC_FILEINFO        0x512
#define ACC_GETFIELDS       0x513
#define ACC_FIELDINFO       0x514

/* Remote MailMerge Protokoll: (Extended-Feature "RM")  */
/*        ACC_ACK Messages sind Teil des Protokolls und */
/*        müssen deshalb verstanden werden!             */
#define ACC_FORCESDF        0x520
#define ACC_GETSDF          0x521

    definitions for the Request/Reply protocol
/* Datentypen des Request/Reply: */
#define RQREP_TYPE_BIN      3
#define RQREP_TYPE_CODE     4

    definitions for the Inquiry protocol
#define DSI_VERSION         0x0100

/* field data-types:
 *    values lower than 128 are 'human readable types' and
 *    values greater/equal 128 are 'machine readable types'
#define FT_CHAR        0x00  /* string                                */
#define FT_DATE        0x02  /* string in _IDT format.                */
                             /* dflt: DD.MM.YY if no _IDT available   */
                             /* For more about _IDT see MINT          */
#define FT_TIME        0x03  /* string: HH:MM:SS                      */

#define FT_BYTE        0x80  /* 2  byte HEX-string                    */
#define FT_UBYTE       0x81  /* 2  byte HEX-string                    */
#define FT_SHORT       0x82  /* 4  byte HEX-string                    */
#define FT_USHORT      0x83  /* 4  byte HEX-string                    */
#define FT_LONG        0x84  /* 8  byte HEX-string                    */
#define FT_ULONG       0x85  /* 8  byte HEX-string                    */
#define FT_FLOAT       0x86  /* 8  byte HEX-string                    */
#define FT_DOUBLE      0x87  /* 20 byte HEX-string                    */
#define FT_ENUM        0x88  /* 4  byte HEX-string                    */
#define FT_BOOL        0x89  /* string: "T" or "F"                    */
#define FT_BITFLD      0x8A  /* at 8 Bit aligned HEX-string           */
#define FT_TIME_T      0x90  /* 8  byte HEX-string (time_t, see UNIX) */

typedef struct {
    int     version;
    char    field_types[32]; /* max. count of 256 fieldtypes are      */
                             /* available (see definements above)     */
                             /* Each bit in this field represents a   */
                             /* valid field-type, where type 0 is     */
                             /* the lowest bit of the first character */
                             /* and type 255 the highest bit of the   */
                             /* last character                        */
} Xacc_Dsi_Request;

typedef struct {
    int     db_anz;          /* count of available data bases         */
} Xacc_Dsinfo;

typedef struct {
    long    db_id;           /* ID of the data base                   */
    char    fname[32];       /* Filename of the data base. if you     */
                             /* are using a GEMDOS or DOS filesystem  */
                             /* it must have a <8.3> format.          */
    char    title[32];       /* A max. 32 byte long description of    */
                             /* the data base.                        */
    time_t  crea_time;       /* The creation date/time of the data    */
                             /* base file.                            */
    time_t  mod_time;        /* The last modification date/time of    */
                             /* the data base structure.              */
    int     n_fields;        /* The number of fields that are         */
                             /* available corresponding to the        */
                             /* requested field typs given by the     */
                             /* ACC_GETDSI message                    */
} Xacc_File_Info;

typedef struct {
    int     fld_size;        /* the count of bits into the field      */
    int     n_fields;        /* The count of field elements           */
    int     elem_size;       /* The length of one field element       */
    char    field_buff[0];   /* from here the list of the <n_fields>  */
                             /* elements follows in this format:      */
                             /* 2 byte <bitno> and <elem_size> byte   */
                             /* description.                          */
                             /* e.g. (<elem_size>=10):                */
                             /*    "\0\1private\0\0\0"                */
                             /*    "\0\2sex\0\0\0\0\0\0\0"            */
                             /*    "\0\4dealer\0\0\0\0"               */
                             /* The value "06" identifies the 2nd     */
                             /* and the 3rd element.                  */
                             /* NOTE that you can't use sizeof()      */
                             /* because of this declaration.          */
} Bitfld_Info;

typedef struct {
    int     n_enums;         /* The count of enum-elements            */
    int     elem_size;       /* The length of one enum element        */
    char    enum_buff[0];    /* from here the list of the <n_enums>   */
                             /* elements follows in this format:      */
                             /* 2 byte <id> and <elem_size> byte      */
                             /* description.                          */
                             /* e.g. (<elem_size>=10):                */
                             /*    "\0Aprivate\0\0\0"                 */
                             /*    "\0Bsex\0\0\0\0\0\0\0"             */
                             /*    "\0Edealer\0\0\0\0"                */
                             /* The value "0042" identifies the 2nd   */
                             /* element.                              */
                             /* NOTE that you can't use sizeof()      */
                             /* because of this declaration.          */
} Enum_Info;

typedef union {
    ulong        n_elems;      /* for types like char,uchar this is     */
                               /* the length of the field               */
    Enum_Info    *enum_info;   /* enum is a special type, which needs   */
                               /* more description than the length!     */
    Bitfld_Info  *bitfld_info; /* a bitfield like used in TA2 for the   */
                               /* info-flags                            */
} Type_Desc;

typedef struct {
    char         id[8];      /* The export-identifier of the corres-  */
                             /* ponding field, i.e. "A1" for the      */
                             /* first address field of Clever or TA2  */
    char         name[16];   /* A short description                   */
    char         desc[32];   /* A long description                    */
    int          type;       /* The data type. Must be one of the     */
                             /* constants defined at the top of this  */
                             /* file                                  */
    Type_Desc    t_desc;     /* This union contains either the length */
                             /* of the field or a pointer to a info-  */
                             /* struct if the type is a special one   */
                             /* like enum or other user-defined types */
} Xacc_Field_Info;

#endif    /* #ifndef __XACC__ */

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