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Text File | 1990-02-04 | 11.8 KB | 397 lines

────────────────────── Zmodem 'Crash recovery' ────────────────────── Explanation : for example, let's imagine that you're in the middle of the downloading of a 200 K file. For some reason, you fall asleep, or, tired of waiting you go out to make a cup of coffee, your child comes and type at the keyboard an Alt-N, or your wife yells at you and disconnect the phone. Horror, you've got only the first 190 K's. Should you call back your favorite BBS and start again the downloading from 0 ? What a waste... but, didn't you know that Dsz have 'Crash recovery' feature : it allows to resume the download at the point where it was aborted priorly. Only the last missing 10 K's will be downloaded to complete the 200 K file. The problem, you ask yourself, how can I exploit this 'Crash Recovery'? - First : no panic, you can make the 'Crash recovery' at any time you want, say, tomorrow when your child is at school and your wife is at the market. - Second: don't touch the truncated file which you've already received. (You can see that it is incomplete by typing at DOS prompt DIR : the truncated file has no date on it ). If you want to check if it is workable with the missing part, copy it to another directory and work on the copy. - Third: make sure that it is in your usual downloading directory. - Fourth: log back onto your BBS. Proceed normaly. For example, on this Opus BBS, at the File section, enter : d z filewant.big where 'd' is the normal Opus download request, 'z' is Zmodem protocol, and 'filewant.big' is the file which download was aborted priorly. ( That's a nicety on Opus that successive commands can be put on a single line, instead of waiting each time for a prompt ). - Fifth: from your comms program, make a shell to DOS. Now, that's here where 'Crash recovery' will be possible. Instead of typing the normal 'dsz rz', enter : dsz rz -r That's all, Dsz will do the rest. Ouf ! ─── With the '-r' option, Dsz automatically check the current directory for 'filewant.big'. If size doesn't match what Opus is sending, Dsz request that Opus send only the missing part and appends it to the file. ─── Since the day I've learned this 'Crash recovery' possibility, I've made systematic use of it. Now, I voluntarily abort huge file downloading, I take a look at the firsts K's to check if I'll want to complete the downloading or no. ────────────── Timing options ────────────── When using Dsz, it may be that you see a lot of 'Time-out', or it may be that the performance of Zmodem file transfer seems bad. ( Performance is bad if at 1200 bauds you get less than 105 char/sec throughput ). The cause may be that your PC is a too fast clone ! Too fast, the protocol 'times-out', and request retransmission of a packet, which in fact is already on the way, at times the same packet is sent over and over even if there's no error. ─── Make a rough check whether your system require timing change or not. Type : dsz d rz ( The 'd' allows to make timing test without being on-line ). After about 10 seconds, you should see the message : Byte -1 retry 0: TIMEOUT Then after another 10 secs : Byte -1 retry 1: TIMEOUT etc. If the time between the TIMEOUTs is less than 10 seconds, your system is probably too fast. To make Dsz timing changes, you may try one or more combination of the following : ┌──> dsz pa10000 d rz { change the "global" timing 'a' parameter } │ dsz z pp500 d rz { change the "in-packet" Zmodem time-out } │ dsz z pt1000 d rz { change the "receiving" Zmodem time-out } │ dsz z pT4000 d rz { chnage the "sending" Zmodem time-out } │ │ ────────────────────────── NOTE: EXPERIMENT WITH THE paX NUMERIC PARAMETER FIRST! THE FOLLOWING IS AN EXCERPT FROM THE DSZ manual: paX Calibrates certain protocol timeouts used with XMODEM and YMODEM transfers (Cybernetic Data Recovery(TM)). This parameter does not affect ZMODEM transfers. The a numeric parameter is automatically set to 2000 for a 4.77 mHz PC or XT, 4000 for a PS2/30, 6000 for an 8 mHz 1ws AT, and 12000 for a PS2/80. If your computer has a speedup card or otherwise runs unusually fast (or slow!) for its type, you may set the a numeric parameter to a value that reflects its speed. EXAMPLE: dsz port 2 pa4000 rb ─────────────────────────── Or you may combine all : dsz pa10000 z pp500 pt1000 pT4000 d rz ( All cases are significant, options must be separated by spaces, and after a 'z' option, all 'p' are related to the 'z' option. Typing "dsz pa3000 z pp100 pt400 d rz" is correct, but "dsz z pp100 pt400 pa3000 d rz" is not ). Try until you find some correct 'pa', 'z pp', 'z pt', 'z pT' values. ─── Hints to facilitate the search of good timing parameters: - For downloading, it is sufficient to change only the 'z pt' parameter. - Start with a big 'z pt' value. With your watch, take note of the time between the TIMEOUTs messages. Divide this time by 10. With the divisor you've calculated, divide your initial 'z pt' value. Example : Suppose that after you type "dsz z pt2000 d rz" you get a timing of 120 seconds between two succesive TIMEOUT. 120 divided by 10 gives 12. 2000 divided by 12 gives approximately 167. Try then with "dsz z pt167 d rz". ─── Once you have find, you should write a batch file which makes the timing settings each time Dsz is called ( otherwise each time Dsz reverts to its default settings ) . For example DSZ.BAT : echo off dsz pa6000 z pt167 %1 %2 %3 %4 %5 %6 %7 %8 %9 In case you use an RZ.BAT batch file which contained : dsz rz %1 %2 %3 Change it to : dsz pa6000 z pt167 rz %1 %2 %3 ─── Note that timing options are different from file transfer options. Timing parameters, just as 'CON' or 'port' or 'speed' options described in DSZ.DOC must precede 'rz', while the "Crash recovery" '-r' option must follow 'rz'. ───────────────────────────── An overview about Dsz options ───────────────────────────── It is easy to understand if you consider that Dsz requires 3 groups of options: - The first group are those related to the system on which you run Dsz, such as timings, which port your modem is connected, etc. With the 'pa', 'z pt', 'CON' etc, you tell the configuration to Dsz. - The second group specifies what you want to be done with Dsz : send or receive, and which protocol you request ( X, Y or Z-modem ). - The third group of option is dependent on the transfer protocol you have requested. You tell what kind of modification to the protocol you want. Thus '-r' Crash recovery is specific to Zmodem. Filenames may or may not be needed, depending on the transfer protocol requested. ─── You can mix as many options as you want. The only important requirement is that the order should be consistent : the options are context-dependent. Thus if you want only to have a look at the default 'p' parameters, enter : dsz p Or you want to look at the default 'z p' parameters, enter : dsz z p Or you want to look at 'p' and 'z p' together, enter : dsz p z p Or if you want to make a Zmodem download with full debugging report, with modem connected to COM2 at 2400 bauds and on a system which require timing fine tuning, the command may be : dsz CON port 2 speed 2400 pa7300 pv9 z pt92 pT1200 rz | | ( 'pv9' means Verbose Level 9 - must not follow a 'z' ). You can put more configuration option between the 'dsz' and 'rz', for example you may insert a 'd' to test off-line, and you may insert lone 'p' to view that the 'pa' is indeed changed to 7300 : dsz CON port 2 speed 2400 pa7300 pv9 p z pt92 pT1200 p d rz | | The first lonely 'p' prints out a list of the 'p' parameters settings. The second lonely 'p', since it follows a previous 'z', it prints out a list of the 'z p' parameters settings. ─── Following is a summary table of Dsz options. A table is convenient to test possibilities in case you need it. More detailed explanations would require the manual, I'm waiting for my registration... ────────────────────── ──────────────── ─────────────── Configuration settings Transfer request Protocol option ────────────────────── ──────────────── ─────────────── CON rz {receive Zmodem} [-abnpr+y] [filename] LARG sz {send Zmodem} [-abnpr+y] wildcard port # rx {receive Xmodem} [-abc+y] filename speed # sx {send Xmodem} [-k] filename d rb {receive Ymodem} [-ab+y] [filename] handshake sb {send Ymodem} [-k] wildcard restrict p?# z p?# ───────────────────── ───────────────── ─────────────── Where # is a number, It should be obvious -a would mean translate ? is a letter. rz sz rx sx ... the end of line (no need Any mixing of the may not be mixed to worry what EOL is on above is valid each system: with the -a option, Zmodem manages itself the translation so that it suits the system, Unix| DOS| CPM) -b binary transfer (it is the default) -r Crash recovery (dont mix with -a option !) -k use 1K blocks -c use CRC -+ append to existing file -n replace destination file if source file is newer -y overwrite existing file -p protect file [ ] means optional, do not type those [ and ] in the dsz command ! Valid mixtures depend on the kind of transfer requested. Thus 'sx' can accept only '-k', while 'rz' may accept '-an'. ─── As an afterthought, it comes to me that in fact Dsz is many programs in one. It would ease users life if a batch menu is written to select options...