Linux TU58 Emulation Source CodeI happen to be a fan of DEC PDP-11 systems. In the 1980's they made a block oriented tape device called a TU58 which used self contained "DECtape II" tape cartridges. This unit could be connected to a PDP-11 or VAX via an RS-232 serial line. Both can boot diagnostics packages from this medium. I created and released an MSDOS based TU58 emulation package. Later I discovered that really I had just reinvented the wheel again as Dan Ts'o of Rockefeller University had already published a BSD Unix TU58 emulator. Source code for this emulator can be found at dbit.com and sunsite. Note that this code contains a copyright notice which permits use so long as it is NOT sold to others.Recently I tried to get this code to work under Linux. It was harder than I expected, and I have not been completely successful. If anyone is interested in looking at the unresolved issues, please contact me. I have ended up with an executable that runs on my Linux 150 MHz box and will boot and run RT11 on a PDP-11/23 at 19200 baud. It also works with an MSDOS based test program, rsp.exe, I originally wrote to test my MSDOS based emulation program. However it does not work reliably with E11 which concerns and puzzles me. I've spent about a week on this project and become frustrated. I do not pretend to be a Linux/gcc guru and could use some help. I thought I would put my efforts in the public domain, hoping someone will see what I am missing. I trust I am not breaking any copyright laws by adding modifications to the original work. In summary, the major change is in the serial port initialization. I created a new main module, lmain.c. Under gcc I can't find struct sgttyb, gtty(), nor stty() which were all called from the original init_device() routine in main.c. My new program, ltu58, can be built with gcc using the new 'makefile'. This makefile also includes commands to build btu58 from the original main.c using the gcc BSD compatibility switches. I had hoped this would work, but as near as I can tell the BSD compatibility does not include the required serial port routines (corrections or additions regarding this comment would be appreciated). I left the original code which attempts to handle permissions if one is not the root user, but I don't think ltu58 works unless its run by root. I made changes in the debug.c file as I couldn't figure out how to get the major and minnor mode of the serial device from the file name under Linux. There is likely a method I don't know, but I just create debug files (if DEBUG is defined) based on the device name. I also made modifications to tu58.c, primarily adding debug statements. However fread() and fwrite() exist in libc, and I renamed these functions by prepending 'tu58' to the names in tu58.c and file.c to avoid conflicts. The only major problem I found was a call in file.c from fposition() to fupdate(). This is done each time the RT11 directory block, 6, is accessed and reopens the emulated tape file. This appears to close the file the program is using and index the global variable fpt out of range. Commenting out this RT11 specific code allowed the program to run successfully with an 11/23 system. There is a comment in the source code regarding this call and in the readme.txt which mentions 'rtpip', a program I know nothing about, any help would be appreciated here also! When I got ltu58 to work with my test program, rsp.exe, I thought I was home free. However I find E11 by John Wilson a very useful test platform, and I can't get ltu58 to run reliably with the MSDOS Demo version of E11 V3.0. I'd like this to work as its a great validation test as well as a good method of creating bootable DECtape II XXDP images. I have followed recent newsgroup discussions regarding E11 and TU58 tape drives which suggest using the /TXMAX:1 switch in the com port assign statement, but this doesn't seem to be the problem. Both my Linux and MSDOS based code sees E11 sending 0xff,0xff where I would expect a break. This does not seem to be a major problem, but ltu58 displays a message about an unknow octal flag 0377 when this occurs. However ltu58 seems to get lost after the 1st or second command packet from an RT11 dir command sent by E11. The programs end up in some sort of deadlock where each is waiting for data. I am suspicious of tu58.c where there is a call from evalflag() to clearbuf() which in turn calls clearcbuf() when the flag TUF_INITF is recieved, but not at all sure this is wrong. Logically flushing the input buffer at this point seems ok, however in my tests E11 seems to have already sent the next command packet when the TUF_INITF flag is seen. Oddly I can sometimes get ltu58 and E11 to work together by adjusting the baud rate. It seems to work at some baud rates and not at others. The E11 throttle setting can also make a difference!
If this puzzle interests you, please pick up the pieces and see what
you can do. I have created a Linux Lha
archive
that includes this descriptive file, the modified emulator source code,
a Linux version of ltu58, and my MSDOS test program, rsp.exe, as indicated
below: Listing of archive : LTU58.LZH
Name Original Packed Ratio Date Time Attr Type CRC
-------------- -------- -------- ------ -------- -------- ---- ----- ----
checksum.c 524 279 53.2% 00-03-01 10:19:14 a--w -lh5- 445C
debug.c 1549 767 49.5% 01-09-04 09:49:26 a--w -lh5- 3562
debug.h 591 230 38.9% 02-02-22 18:13:52 a--w -lh5- 497D
file.c 4830 1902 39.4% 02-02-27 15:01:56 a--w -lh5- 07FC
io.c 2239 889 39.7% 00-03-01 10:13:52 a--w -lh5- 5EAD
lmain.c 5827 2524 43.3% 02-02-21 17:14:22 a--w -lh5- F95E
ltu58 44730 16818 37.6% 02-02-27 15:08:52 a--w -lh5- FEC1
main.c 2871 1266 44.1% 00-03-01 10:16:04 a--w -lh5- A1B1
makefile 1315 534 40.6% 02-03-01 10:37:44 a--w -lh5- 28D1
readme.txt 2276 1204 52.9% 01-09-01 14:34:36 a--w -lh5- F282
rtdir.h 1000 320 32.0% 00-03-01 10:15:30 a--w -lh5- 642C
tu58.1 1166 595 51.0% 00-03-01 09:53:14 a--w -lh5- 79E5
tu58.c 6687 2616 39.1% 02-02-27 15:08:36 a--w -lh5- CB90
tu58.h 2777 1204 43.4% 01-09-03 10:48:22 a--w -lh5- 3CEF
RSP.EXE 86073 41398 48.1% 01-05-13 11:55:48 a--w -lh5- B04C
CONSOLE.INI 34 34 100.0% 00-02-24 21:40:40 ---w -lh0- B8DE
LTU58.HTM 9616 4375 45.7% 02-03-01 12:06:12 a--w -lh5- 7AC9
-------------- -------- -------- ------ -------- --------
17 files 172497 76241 44.2% 02-03-01 11:52:08
The following files are identical to the original distribution, but the
time stamps have inadverantly been changed:readme.txt, tu58.1 - these are documentation files main.c, checksum.c, io.c, debug.h, rtdir.h, tu58.h The original distribution also included empty.c which is not required for the Linux build.
Build ltu58 under linux via "make ltu58". RSP.exe and console.ini are the only MSDOS files included. Source code for my rsp.exe is available if anyone is interested, but its not real exciting. It initializes the COM port based on the console.ini file contents, a sample for COM1 at 9600 baud on irq 4 is included. The irq line may be omitted, in which case the PC defaults are used. The program is interactive and will test most RSP (radial serial protocol) commands. The first letter of each interactive operation triggers the operation. Several prompt for more data, ie start block and number of bytes. The default mode is to dump any input on the serial line in hex to the screen. For example, issue a read command by pressing 'R' and it will prompt for the start block and # of bytes desired. Then send RSP packet commands to the host and dump the data it returns to the screen. Copy, 'C' is an exception in that it writes the data packets to a file rather than dumping to the screen. One can copy all or a portion of an emulated TU58 tape this way, and it seems to work fine with ltu58 at 19200 baud! Conversely Write, 'W', will copy blocks from a source file back to the emulated TU58 tape. |
PDP-11 >