Serial Backup
Incremental backups for your CP/M system over the serial port
Back in the day, I backed up the files on my ST251N hard drive to floppies. Somewhat to my surprise, 28 years later they were all still readable. But having a finite supply of 5.25" floppy discs, and a handy Linux system standing by with essentially unlimited disc space, I started to get ideas... and Serial Backup was born.
Serial Backup uses a serial link to backup files using Ymodem batch protocol. It sends files that haven't yet been backed up to a remote system. Using Ymodem allows batch sends, and (for anyone running ZRDOS or ZSDOS) the preservation of file timestamps. After each file is successfully sent, its archive bit is set, so it won't be backed up again until/unless it's modified.
Serial Backup logs in to the remote system, starts up its Ymodem program in receive mode, sends all the files modified since the last backup, and logs back out again. The commands that are sent to the remote system are contained in a configuration file so you can customise them to your particular setup.
If run under a ZCPR3.3 system (with a copy of Turbo Pascal patched to have a ZCPR3 header), the program will use the drive map and maximum user number contained in the Z3ENV block. If you're using ZSDOS, it will send each files' modification timestamp as it's backed up. But it will run just fine under vanilla CP/M 2.2 as well (you can define your drive map and maximum user number in the configuration file).
The configuration file
Serial Backup assumes its configuration file is called A:BACKUP.CFG. Since I use ZRDOS and ZSDOS, I set it up as a public file, so it's accessible no matter what user area I happen to be operating in.
| Keyword | Use | Parameter |
|---|---|---|
| Timeout: | Time to wait after each command response | Tenths of seconds to wait after each command |
| ModemTest | Include to test that modem is offline | none |
| ConnectIn: | Command to send on connection (maximum of 5) | Command (up to 40 characters) |
| ConnectOut: | Response to command on previous line | Expected command response |
| DisconnectIn: | Command to send on disconnection (maximum of 5) | Command (up to 40 characters) |
| DisconnectOut: | Response to command on previous line | Expected command response |
Here's an example configuration file:
Timeout:5
ModemTest
ConnectIn:ATDT<<your system name here>>
ConnectOut:login:
ConnectIn:<<Your username here>>
ConnectOut:Password:
ConnectIn:<<Your password here>>
ConnectOut:$
ConnectIn:cd backup
ConnectOut:$
ConnectIn:rz --ymodem -b -y
ConnectOut:receive.
DisconnectIn:exit
DisconnectOut:NO CARRIER
And here's the kind of thing you'd see if you ran the program with that kind of configuration file:
B0:>backup
ATDTlinuxbox
DIALLING linuxbox.mynetwork.com:23
CONNECT 4800
linuxbox login: backupuser
Password:
Last login: Sun Oct 11 16:30:07 CDT 2020 from ampromodem.mynetwork.com on pts/0
No mail.
backupuser@linuxbox:~ $ cd backup
backupuser@linuxbox:~/backup $ rz --ymodem -b -y
rz waiting to receive.
a/f/ease.var 12K
b/f/backup.pas 2.9K
b/f/remote.pas 7.0K
b/f/readme.md 2.8K
b/f/readme.bak 1.6K
b/f/remote.bak 7.0K
b/f/backup.com 19K
b/f/backup.cfg 384
exit
logout
NO CARRIER (00:02:20)
B0>
Patching Turbo Pascal with a ZCPR3 header
Adding a ZCPR3 header to Turbo Pascal is a simple matter of replacing 8 bytes starting at address 0103 (hex) in TURBO.COM. The sequence to be replaced is
0103:5A 33 45 4E 56 01 00 00
You can do this with your favourite binary file editor, or even with DDT.
Patching TURBO.COM in this way and then compiling Serial Backup allows it to access the Zsystem's environment block. This allows the utility to retrieve both the drive map and the maximum user number.
ZRDOS and ZSDOS support
Adding support for ZRDOS or ZSDOS is even easier than adding ZCPR3 support. All you have to do is: nothing. The utility automatically detects when it's being run under ZRDOS or ZSDOS and sends the file modification timestamps.
Paths
Serial Backup sends the drive letter and user number along with the file name. If you're backing up B4:FILE.TXT, the filename that's sent is "b/4/file.txt". The Ymodem program on the remote system must accept a full pathname and create subdirectories as needed (Linux's rz does this out of the box.)
Serial port
Serial Backup assumes that your serial device is available through the reader and punch logical devices, and, as such, through the Aux device in Turbo Pascal.
Serial port speed
One thing that Serial Backup doesn't handle is setting the speed of the serial port. It just uses the port at whatever speed it was previously set to. With no consistent way to set the serial port speed, it's left to an external program to do this.
Serial port input status
As there's no equivalant to the CONST BDOS/BIOS call for the reader device in standard CP/M, you'll have to roll your own. Somewhere in your BIOS is a routine that checks to see if there's a character available from the reader device. You have to track it down and figure out how to call it from the ModemInReady routine in mdminrdy.pas. It may be an extended BIOS call, it may be a port you'll have to read, it may even be a memory location to check for the number of characters available in an interrupt serviced input FIFO.
If your BIOS implements the CP/M IObyte, and allows for switching the logical console device (CON:) to the reader and punch (TTY:), you could try altering the IObyte on the fly to switch CON: from CRT: to TTY:, and then using the BDOS CONST call to see if the reader has a character available. I haven't tried it, but in theory it sounds like it would work.