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Documentation for XPRBIModem.library Version 1.01, 04 Sep 1992, Dirk Peterson 1. Introduction (or "What is this thing, anyway?") --------------------------------------------------- XPRBIModem.library is an Amiga shared library (with full Lattice C source code) which provides BIModem file transfer capability to any XPR-compatible communications program. The XPR external protocol standard describes an interface method which allows various file transfer protocols to be implemented as Amiga shared libraries which may then be used interchangeably in any compatible communications program. This takes a heavy load off of the comm program author, who no longer has to support scads of different file transfer protocols (many of which are quite tricky to code) in their program in order to make it widely useful and popular. The comm program is also smaller and more efficient as a result, since all those obscure protocols (you know, the ones *you* don't need) are no longer taking up space. The XPR standard also helps users, who can mix and match their favorite file transfer protocols (and implementations thereof) with their favorite comm programs. And when new protocols are invented, the user simply plugs in a new library, and voila!, it's ready to use. Hopefully, making protocols easy to support will allow more and better comm programs to be written, as authors can concentrate on their programs instead of constantly re-inventing the wheel. Of course, for all of this wonderful stuff to happen, there needs to be a good selection of these XPR protocol libraries available to the public. It's the classic chicken-and-egg problem; comm program authors won't be motivated to support the XPR standard unless there are a goodly number of protocols available for it. And other programmers won't be motivated to write XPR protocol libraries until there are a goodly number of comm programs which can use them. In an effort to do my bit [ B^) ] for the Amiga community, which has given me so many neat toys to play with over the past few years, I decided to try and help get the ball rolling. Hopefully, the early availability of a BIModem library will help stimulate interest in the XPR standard, resulting in better Amiga telecomms for all of us. And by making my source code PD, I hope to help others interested in writing XPR protocol libraries by giving them some serious example code. Also, having BIModem library code readily available to John Q. Hacker should help ensure a steady stream of new lemon-fresh enhanced BIModem libraries (with enzymes) for all of us to use in the future. Of course, no discussion of the XPR standard would be complete without giving proper credit to the author, Willy Langeveld of the Stanford Linear Accelerator Center. Many thanks are due him for this effort. If you have any further questions about the XPR standard, be sure and download the spec; it should be available on BIX (since he's a sysop there), or on most other major systems. And I'll try to keep the current version available on my BBS, as well. All files in this archive which are not copyrighted are hereby released to the public domain (which they were anyway, by way of not being copyrighted, but I want to make sure YOU realize that). Do as you like with them. Please make lots of copies and distribute them all over the place, and make lots of derivative works, and everything! Heck, you can even publicly perform and/or display this code if you can figure out how... 2. Installation (OK, enough chatter; let's get to work) -------------------------------------------------------- Couldn't be easier. Just copy the XPRBImodem.library file into your LIBS: directory. All XPR-compatible comm programs should provide a way for you to select which XPR protocol you wish to use, either by giving you a file requester showing LIBS:xpr*.library, or by automatically detecting these libraries and adding them into their menus. WARNING: Versions of VLT prior to revision 4.107 had a bug in the xpr_sflush() routine which caused random Guru 3 crashes on some systems. If you're using a version of VLT older than 4.107, it would be a good idea to upgrade to the latest rev. Besides, there's a bunch of new features you're missing, anyway... ANOTHER WARNING: Versions of VLT prior to 5.034 had a bug in the xpr_sread() function which caused them to (at least sometimes) fail to return any bytes received so far when an xpr_sread() call timed out. This version of XPRBIModem.library requires VLT version 5.034 or later. (Yes, Willy, it really was broken B-)) 3. Options ----------- The XPR standard lays out two ways for the comm program user to specify options for the XPR protocol. The more primitive option is for the comm program to provide a method of passing an option string to the XPR library before transferring files. The precise format and usage of this option string is left up to the XPR protocol author; the comm program just sends it verbatim. If an environment variable is found with the same name as the XPR protocol (i.e. there's a file in the ENV: directory called "XPRBImodem"), the comm program is supposed to use this string (contents of file) to initialize the protocol options. Also, a menu option or some such should normally be provided which will allow the user to be prompted for the option string interactively. Version 2.0 of the XPR standard created a new, more sophisticated way for the comm program user to specify XPR options. If the comm program supports it, the XPR library can give the comm program a list of option prompts, and the comm program can then let the user interactively set the various options individually, possibly even using nice gadgets and stuff. In any case, no matter how your particular comm program feels like handling it, these are the options supported by this implementation of BIModem: T{Y|N|?|C} Text translation mode: TY = Text Yes; if receiving, translate CR/LF pairs or solo CR chars to normal Amiga LF chars. Ignore data past ^Z. If sending, suggests to receiver that they should receive this file in text mode. TN = Text No; receive file verbatim, without changes. If sending, suggest to receiver that they receive this file verbatim, without translations. T? = Text status unknown; if receiving, use sender's suggestion as to whether to do EOL translations or not. If sending, tell receiver to use default mode, 'cause we don't know either. TC = Text mode set by Comm program; the library asks the comm program whether or not to use Text mode for each file. If the comm program doesn't support the necessary xpr_finfo() call, or if the call fails, this option acts like T?. From the user's point of view, what this option normally does is set the Text mode to match the comm program's built-in text/binary/end-of-line/translation mode, if any. O{Y|N|R|S} Overwrite mode: OY = Overwrite Yes; if about to receive file with same name as one which already exists, delete the old file and receive the new file in its place. ON = Overwrite No; if about to receive file with same name as one which already exists, append ".dup" onto the name of the new file to keep them separate. OR = Overwrite Resume; if about to receive file with same name as one which already exists, resume receiving file data from the current end of the existing file. OS = Overwrite Skip; if (etc.), tell sender never mind, skip this file, we don't want it. Batch transfers will move on to the next file in the set, if any. Bnnn Buffer size: XPRBIModem.library adds a layer of file I/O buffering in addition to whatever the comm program may or may not provide. This option sets the size of XPRBIModem's file I/O buffer in kilobytes. The minimum value is 1 KB, for those using RAM drives or fast hard drives, or those whose comm programs already provide sufficient buffering. The maximum value is as much contiguous RAM as you have available in your Amiga. If you specify more than is actually available, XPRBIModem will keep decrementing the buffer size requested by 1 KB until the memory allocation works. That way, if your RAM is too fragmented to use the amount you request, XPRBIModem simply uses the largest block available. Buffering is especially helpful for floppy drive users; it keeps your drive from continuously gronking and slowing things down all through the transfer. NOTE: Versions of VLT prior to 5.034 couldn't handle buffer sizes >= 32 KB. If you wanted to use larger buffers before and couldn't, try again now. Fnnn Frame size: Although normally avoided, BIModem has the ability to require an ACK to be sent from the receiver to the sender every X-many data bytes. Normally you don't want to use this feature, because not waiting for ACKs is part of how BIModem works so fast. However, this feature can be very useful in conjunction with file I/O buffering on slow devices (namely those floppy drives). If you set up a large I/O buffer to avoid gronking your floppy so often, you'll find that when the buffer finally *does* get around to being flushed that it can take a looonng time; so long, in fact, that the delay can cause timeouts and errors. But if you set your BIModem to require the sender to wait for an ACK every buffer's-worth of data, the sender will politely wait for you to flush your buffer to the slow floppy and send it an ACK saying it's OK to continue now. This value should be set to 0 to disable ACKs (normal mode), or set it to the actual number of data bytes allowed between ACKs. For example, if you set B64 because of your floppy, you should also set F65536. Ennn Error count: This allows you to set the number of sequential errors which will be required to convince BIModem to abort the transfer. The normal value is 10, meaning that 10 errors must happen in a row with no valid data being transferred in order to cause an abort. This setting is provided for those using XPRBIModem with a BBS, who may wish to use a relaxed setting, or those with really lousy phone lines who are desparate and patient enough to want the transfer to continue in spite of horrible performance. A{Y|N} Auto-activate mode: AY = Auto-activate Yes; if the comm program supports the ability, the library will automatically go into receive mode when the start of a BIModem download is detected. AN = Auto-activate No; don't try to automatically start downloading, make the user activate it. D{Y|N} Delete after sending: DY = Delete Yes; delete each file after it has been sucessfully sent. DN = Delete No; don't delete files after sending them. K{Y|N} Keep partial files: KY = Keep Yes; keep the fragment of a file received so far if file reception is aborted. This allows you to use the Overwrite Resume option above to pick up where you left off on your next attempt. KN = Keep No; delete any partially-received file after an aborted transfer. S{Y|N} Send full directory path: SY = Send path Yes; send full filenames including directory path to receiver. SN = Send path No; send only simple filenames, not including directory path. R{Y|N} Receive full directory path: RY = Receive path Yes; use full filename exactly as received, instead of using the P option directory path. RN = Receive path No; ignore received directory path (if any), use P option directory path instead. P{dir} Path to use for received files: Px = Store all received files in directory "x" if option RN set. Ignored if option RY set. "x" can be any valid existing directory, with or without trailing "/" (e.g. "Pdf0:", "PComm:hold", etc.). If setting the options via the option string method (either ENV: file or primitive comm program), note that the setting for each option must immediately follow the option character with no intervening characters ("TY", not "T Y" or "T=Y"). When setting multiple options at once, separate the options from each other with commas and/or spaces; for example, "TN,OR,F0". You don't have to specify all options every time; the options you specify will be merged into the current option settings, replacing their old values. Upper/lower case is not significant. The default option settings if you don't change anything are "TC, ON, B16, F0, E10, AY, DN, KY, SN, RN, P". If the comm program supports the xpr_options() call added in version 2.0 of the XPR spec, you should be prompted for each option with a nice prompt message such as "Text mode (Y,N,?,C):" and possibly be able to use Intuition string and/or button gadgets instead of being stuck with the semi-cryptic option string format described above. 4. Serial port settings ------------------------ BIModem (at least this implementation of it) requires that your serial port be set to 8 data bits, no parity, 1 stop bit. This allows BIModem to send full 8-bit binary data bytes without having them munged on the way through the modem. If your comm program supports the xpr_setserial() function, XPRBIModem will use it to set your serial port to 8N1 before doing a transfer, and will set your port back the way it was again after it's done. If your comm program doesn't support xpr_setserial(), you'll need to make sure it's in 8N1 mode yourself. BIModem works well in all serial port handshaking modes; none, XON/XOFF, or 7-wire/RTS/CTS. Since any or all of those handshaking modes may be appropriate at different times, with different modems or remote systems, XPRBIModem lets you set the handshaking mode and doesn't mess with it. 5. Receiving files ------------------- Once you get the BIModem options and your serial port configuration set up properly, you're ready to actually use this thing (gasp!). Receiving files via BIModem is quite simple. First, get the file sender going by using whatever command it wants. BIModem is a batch file transfer protocol, meaning that it's capable of transferring several files in a single exchange, so the remote system may allow you to specify multiple files to be sent to you at one time. It may also allow you to use wildcard characters in the filename(s); this is all system dependant. This may be all you have to do. If you specified option AY (auto-activate on), and your comm program supports it, XPRBIModem should automatically activate at this point and start receiving your files. If you specified AN, or your comm program doesn't support auto-activation, you should now use whatever option your comm program provides to activate file reception; this will usually be a menu option or button gadget. Either way, once XPRBIModem starts receiving files, it should automatically receive all of the files you specified into the proper directory as indicated by the R and P options. Make sure that you have set the BIModem options properly before starting the transfer; especially, make sure you only use TY if you know that all of the files being transferred in this batch are printable ASCII text files. If you use TY on normal binary files like .ARCs or .ZOOs, they'll be mangled beyond use. 6. Sending files ----------------- Sending files using BIModem is fairly straightforward. First, activate the file receiver with whatever command the remote system requires. You may or may not need to specify a filename or directory to the remote system; this depends on their implementation of BIModem. Once the remote system is ready to receive files, activate your comm program's BIModem send function. Your comm program will prompt you for which file(s) to send. Although BIModem is a batch protocol, your comm program may or may not allow you to specify multiple file names to be sent; also, wildcards may or may not be supported. These decisions are up to the comm program author; BIModem will handle multiple files and wildcards if the comm program allows them. Once you've specified the file name(s), the file(s) will be sent to the remote system. Note that the T option serves only as a suggestion to the receiving system when sending files; the receiver makes the final decision as to whether to take your advice or to force the files to be received in text or binary mode. If errors occur while sending the file(s), you'll probably notice a small enhancement I made to the normal BIModem error recovery procedures. Normally, file transfer protocols have to compromise between efficient data transmission on good, clean phone lines and quick error recovery on bad, noisy phone lines. If you pick a large packet size, you get high throughput on clean lines due to low packet overhead, but you have slow recovery times and large amounts of retransmitted data on noisy lines. If you've used YModem on noisy lines you've seen this problem. But, if you use small packets to reduce retransmitted data on noisy lines, you increase the amount of time the protocol spends sending packet overhead, and your throughput suffers. The solution is to vary the block size according to the experienced error rate during the transfer. That way you aren't stuck with a rigid packet length which will sometimes be the wrong size no matter what. I came up with this idea back when I first wrote the BIModem code for Opus, and cleared it for future compatibility with BIModem's designer, Chuck Forsberg, back then. Since then the basic concept has been extensively tested in the Opus BBS system, and has proven quite effective; it has also been incorporated into various other BIModem implementations over time. The actual algorithm for deciding what size packets to use when is pretty much up to the protocol author; XPRBIModem uses a modified version of the Opus algorithm which prevents locking the packet size at a small value when a large one-time burst of errors occurs. 7. Notes for comm program authors ---------------------------------- That's pretty much everything you need to know in order to use XPRBIModem properly. Here are some notes for the "other" XPR standard users, namely the comm program authors: Certain XPR callback functions *must* be implemented by the comm program author in order for XPRBIModem to be used. If any of these functions are not supported by your comm program, XPRBIModem will display an error message and abort when invoked. These required functions are: xpr_fopen(), xpr_fclose(), xpr_fread(), xpr_fwrite(), xpr_fseek(), xpr_sread(), xpr_swrite(), and xpr_update() The xpr_update() function provides many data fields for your comm program to potentially display to the user. These are the XPR_UPDATE struct elements which XPRBIModem will keep updated during transfers: xpru_protocol, xpru_filename, xpru_filesize, xpru_msg, xpru_errormsg, xpru_blocks, xpru_blocksize, xpru_bytes, xpru_errors, xpru_timeouts, xpru_blockcheck, xpru_expecttime, xpru_elapsedtime, and xpru_datarate As you can see, XPRBIModem tries to provide as many status fields as possible. Although all of them are useful, the ones which are most important to BIModem users are filename, filesize, msg and/or errormsg, and bytes. Please try to provide at least these fields in your status display, plus as many of the rest as you can manage. Although only the XPR callback functions listed above are crucial for XPRBIModem, almost all of them are used if they are provided. Although XPRBIModem will function without any of the other routines, its performance or capabilities may be degraded somewhat. Specifically, this is what you give up if you choose not to supply any of these other XPR callback functions: xpr_sflush(): Used when performing error recovery and resync when sending files. If not provided, extra timeout errors and delayed error recovery will be likely. The files will still be transferred properly, but errors will degrade overall throughput more than usual. xpr_chkabort(): Called between sending or receiving packets. If not provided, there's no way for your comm program user to abort a transfer in progress except by trying to somehow force it to decide to give up and abort on its own, such as by turning off the modem and hoping the protocol will abort after enough timeouts (it will, eventually...). xpr_gets(): Called to prompt the user interactively for options when your comm program invokes XProtocolSetup() with a null xpr_filename field (if xpr_options() isn't available instead). If not provided, you'll have to prompt the user for the options string yourself, and pass this string in xpr_filename when invoking XProtocolSetup(). xpr_setserial(): Called to obtain the current serial port settings, and to change the serial port to 8N1 if it's not already set that way. If not provided, XPRBIModem will assume all transfers are being done at 2400 bps, which won't hurt anything, and your users will have to make sure that the serial port is set to 8N1 themselves. xpr_ffirst() and xpr_fnext(): If either of these routines are missing, XPRBIModem will lose the ability to send multiple files in a batch. The xpr_filename pointer passed to XProtocolSend() will be assumed to point to the actual full filename of the single file to be sent in this batch. If both of these routines are provided, XPRBIModem will rely upon them completely to obtain the names of the files to send, and the xpr_filename pointer will not be used for any purpose by XPRBIModem except to be passed to ffirst/fnext. This gives your comm program a way to send not just a single filename template's worth of files in a batch, but a list of different filenames. If, for example, you set xpr_filename to point to the first node of a linked list of filenames and/or templates to be sent, rather than just having it point to a string, you can have your ffirst and fnext routines traverse this linked list in order to determine the next file to be sent. Or you could have xpr_filename point to a buffer containing a list of filenames separated by commas, and your ffirst/fnext routines could return each filename in this list in turn. The key here is that if you provide these two routines, you're in complete control over the series of names fed to XProtocolSend. If you omit these routines, XPRBIModem is stuck with single-file mode. Once again, if these two routines are provided, XPRBIModem will *always* call them; it makes no attempt to use the xpr_filename pointer for anything itself. This is not explicitly spelled out in the XPR standard, but it seems the only reasonable way to handle batch protocols to me. Hopefully other XPR library authors will follow this precedent as well, so that comm program authors will be able to count on multiple-filename batch sessions being handled properly. xpr_finfo(): Used to determine the filesize of files being sent, in order to tell the receiving system how big they are. Also used to determine the size of a file which already exists when in Overwrite Resume mode; XPRBIModem must be able to get the size of the current portion of the file in order to be able to tell the sender where to resume sending from. If this routine isn't provided, Overwrite Resume mode is not allowed. This routine is also used to check if Text mode should be set to Y or N for each file when option TC is set. xpr_options(): If you don't supply this, users will be stuck with setting the library options via the semi-cryptic text string method (ENV: and/or xpr_gets()). This routine and xpr_update() have a lot to do with the look and feel of your program when using XPR libraries; any skimping on these two routines will be painfully obvious to the user. Conversely, doing a nice job on these two routines will really make your program shine. xpr_unlink(): Required by the DY and KN options, so if you don't supply it, those options are not allowed.