Slowdos v2.x (hereafter referred to as Slowdos), is an extension to +3 BASIC which allows MSDOS discs to be read and written from BASIC
Although there have already been a couple of programs which can be run on the +3 which allow MSDOS discs to be used, they are limited in scope: The original Slowdos only copied files, and MSODBALL (by John Elliot) runs only from CP/M and uses an obscure format which could be read by both MSDOS and CP/M.
Enter in here Slowdos, the program which allows all manner of functions to be performed on MSDOS discs from BASIC.
Slowdos will run on any +2a or +3 (hopefully regardless of issue), however for practical usage a +3 with an external disc-drive is recommended.
The external drive should be double-sided and capable of reading 80 tracks ie a DSDD disc-drive. Slowdos has been developed with 3.5" drives in mind, though there is no reason why it shouldn't work with a DSDD 5.25" drive.
It is possible that Slowdos will work with single density drives, although they to all intents and purposes obsolete, but I make no guarantees as to data integrity.
A definitive list of commands now follows, it is not intented to be a tutorial as to how to use them, it is presumed that the concepts behind them is already known from use of the equivalent +3 commands.
Key to symbols used:
a(n) = 16 bit number dd = drive no 1,2,* f = filename u1 = source filename u2 = destination filename ss = stream number
All parameters in parenthesis [ ] are optional.
CAT [#ss,]dd"f"
Catalogues a disc, to stream ss (default is the screen), the file name may be wild. The displayed format is identical to that of a normal +3 drive. NB Hidden (system) files are automatically shown.
LOAD Pdd"f"
Load a file from the disc, all the usual BASIC extensions may be used ie CODE, DATA, SCREEN$. In addition the extension S can be used to load a 48k snapshot.
The snapshot format is the .SNA format, supported by all emulators and is the de facto standard for 48k snapshots.
SAVE Pdd"f"[!]
Save a file to disc, as with LOAD all the usual BASIC extensions may be used. If ! is specified before any of the BASIC extensions then the file is saved without a PLUS3DOS compatible header
MERGE Pdd"f"
Merge a BASIC file on disc with the one in memory
ERASE Pdd"f"
Erase the file f from the disc
FORMAT Pdd[!][;"f"]
Format the current disc in DSDD MSDOS format. Confirmation is asked prior to formatting. If ! is specified then the disc will not be formatted, but merely initialised. The filename f is the disc name, this is not used by Slowdos, but is provided for ease of use of Slowdos formatted discs on other machines.
ERASE Pdd"u1" TO "u2"
Rename the file u1 giving it the name u2
MOVE Pdd"f" TO #ss
Copy the file f to the stream ss, note that file filtering takes place, all character codes below 32 are replaced with a space.
COPY Pdd"u1" TO "u2"
Copies the file named u1 on the MSDOS disc to the file named u2 on the default +3 drive. u2 may be a drive in which case u1 can be wild, keeping the original filenames. Note that all the files saved on the +3 disc will be saved with PLUS3DOS headers, and if appropriate the headerdata filled to create files loadable by +3 BASIC. The default for unrecognised files of length shorter than 65535 bytes is to be a code file with a load address of 0. 48k snapshots are saved as filetype 4.
COPY "u1" TO Pdd[!]["u2"]
Copy the file u1 from the default +3 drive to the MSDOS disc. If u1 is wild then omit u2. If the ! parameter is supplied then the files saved on the MSDOS disc will be headerless.
LOAD @dd,tt,ss,aa
SAVE @dd,tt,ss,aa
These commands are used for reading/ writing disc sectors from memory. tt is the track, 0 - 79 (side 1), 80-159 (side 2). ss is the sector number (1-9), and aa is the memory address in memory configuration 5,2,0 (normal configuration)
MOVE TO Pdd"f"
Change directory, equivalent to the CD command on larger computers. Inside each subdirectory there are always two files. A "." file which refers to the current directory and a ".." which points to the parent directory.
A full path may be specifed by stringing directories together thus:
MOVE TO pdd"dir1/dir2/dir3...."
Note the use of the / not \ - this is in line with all real operating systems, UNIX, VAX, AmigaDOS etc
To move back to the root directory leave the pathname out or make it null.
Once inside a subdirectory, usage of Slowdos is not affected, it is still possible to load/save/copy/rename etc files.
VERIFY Ddd"f"
This commands are inoperative, they pass syntax to avoid problems with programs that do use them.
POKE @a1,a2
Does a 16 bit poke for the entire memory configuration (ROM3, pages 5,2,7). This command is mainly supplied for small patches to Slowdos (should they be needed), however it does have other uses - try POKE 60433,col and POKE 60431,col to change the editing colours for the top and bottom of the screen.
Slowdos accesses a number of file formats used by emulators on other machines. The most common of these is the snapshot file, the usage of this was detailed above, but to recap:
LOAD Pdd"f"S will load a 48K .SNA file and lock the machine in 48k mode.
LOAD Pdd"f"S! will load a 48k .SNA but will not lock the +3 in 48k mode. If you manage to break out of the program then the chances are that you will be in 48k mode, but you can return to 128k with Slowdos running via a PRINT USR 23354. Please note with this that crashes/spurious effects may sometimes result whilst using the snapshot due to the fact that data in the printer buffer isn't loaded.
Slowdos also supports the .TAP file format. A TAP file is in essence an image of a cassette tape, and is often used to preserve the loading screen of a game, it is also used by Alchemist Software to distribute Alchnews for use on emulators.
Slowdos treats TAP files as (limited) sub-directories, limited in the respect that they are not random access nor can a CATalogue be performed. However it is possible to copy files out of a TAP file to +3 disc.
To enter a TAP file use the command
MOVE TO Tdd"f"[IN]
Please note the use of T and not P (as for subdirectories). The filename f must have the extension .TAP.
Once inside a TAP file the command LOAD P*"" may be issued to load the first BASIC file found within it. As you may have deduced it is necessary to prefix the filename with a P* - this is so as to fail +3 syntax and to pass the command to Slowdos. As a result it should be obvious that any program within the TAP which loads files from BASIC will have to slightly modified
- namely the P* inserted before the filename. I believe that this is a minor inconvenience when compared to the flexibility that being able to access a TAP file provides.
Following logically, any program which loads headerless files will not work, however it is possible to copy headerless files to +3 disc, and then modify the program so that it does work on a +3 - in essence converting the program back to its native computer. The syntax of the COPY command is exactly the same as for dealing with normal directories.
MOVE TO Tdd"f"OUT
This is a very powerful command which allows files on the +3 to export files for use with emulators.
The file format used is (not unsuprisingly) the .TAP format, to use it you can either copy files to it, or save files into it.
To close the .TAP file (when all the files are enclosed) do a MOVE TO Tdd. The file will automatically be closed, and the directory entry written. Please note that if you forget to do this, then the .TAP will not be accessible, but space on the disc will have been allocated.
As a little note to avoid any potential confusion, if you are reading a .TAP file, any writing will take place in the current directory, and if you are writing a .TAP file any reading will access the current directory (on the MSDOS disc).
Unfortunately due to memory constraints it isn't possible to copy files into a .TAP file from an MSDOS disc (and vice versa).
Throughout the list of commands reference has been made to drive numbers, however, since the +3 only supports one external drive, there is only one MSDOS drive,and thus p1 and p2 access the same physical drive.
Although the external drive is used by Slowdos, it is still possible to perform +3 DOS functions on the B: drive, though obviously it isn't possible to use both drives at the same time eg copy from B: drive to MSDOS disc.
To this end, and in order to prevent corruption of +3 discs, only discs which match a template MSDOS disc format will be used by Slowdos, which rejects for use as MSDOS disc any BFORMAT +3 discs. (Obviously it is possible to reformat these discs for use by Slowdos).
All of the routines are fully error trapped and will return to BASIC with a harmless error message should anything untoward occur. In addition the RIC messages from +3 DOS have been disposed of, any errors now result in an error message.
It is well known that the +3 has problems driving certain printers. A set of pokes was found which solved the problem, however these shouldn't be used when Slowdos is installed (crashes may result if you do), instead use POKE @49286,16 which will enable these problem printers to work. - Please note that this POKE has changed from earlier versions of Slowdos and DiSCDOS.
Slowdos survives the 128k NEW command, and need only be reloaded if a reset is performed.
Slowdos occupies the second screen (in page 7), and as such nothing should be placed there lest the +3 crash in an interesting manner! It also uses some additional space in page 7, this doesn't interfere with normal usage of the +3 though it may cause some problems with other programs.
Because of the +3 CAT syntax problem any CAT phrase involving a numeric variable will not be able to be entered unless the variable(s) exists. All other comands are unaffected, so the value of remedying it seems dubious.
v1.0 Original version of program released back in 1994 ??.8.94 v1.1 Bug release ??.12.94
v2.0 Crippled demo version of the new Slowdos 5.12.97
v2.1 Fully featured version of the new Slowdos 7.12.97 (intern)
v2.2 Added .TAP, subdirectory support. Added the ! option 16.12.97 to snapshot loading. Optimized the code a lot.
v2.3 Added writing to .TAP files, added in system calls 2.3.98 (see Appendix II), incredible amount of optimization made - some 300 bytes saved! Sorted out erasing of files created on Sparc stations, cleaned up a potential problem in SAVEing of arrays.
v2.4 Full compatibility with +3B Syntax ROM, 24.2.2001 either english or spanish version
The snapshot format supported by Slowdos is the common used .SNA format derived from the Mirage Microdriver format. This is the de facto standard for 48k snapshots and is supported by all major emulators.
The format of the file is as follows:
Offset Bytes Description
0 1 i
1 2 hl'
3 2 de'
5 2 bc'
7 2 af'
9 2 hl
11 2 de
13 2 bc
15 2 iy
17 2 ix
19 1 Interrupt (bit 2=IFF2 1=EI/0=DI)
20 1 r
21 2 af
23 2 sp
25 1 Intmode (0=im0/1=im2/2=im2)
26 1 Border colour
27 49152 Ram dump (16384...65535)
As of v2.3, Slowdos gives you, the programmer, the ability to access MSDOS discs in a simple way, without having to write your own routines. Via these system calls you can do whatever your imagination allows - for example you could read different emulator file formats or you could write a file manager! - It's up to you!
All of the calls, are referenced by calling address 49155 in page 7 with l holding the routine number, at the moment, the following routines are accessible:
1, r_mslog
Entry parameters: none Exit parameters: standard
Log an MSDOS disc in, read in the FAT, check format
2, r_getpar
Entry parameters: none Exit parameters: de=address of header in page 7
Get the address of the file header in page 7, this is 7 byte block ala +3 DOS as is arranged as follows:
|----------------|-----|-----|-----|-----|-----|-----|-----|
| Byte | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|----------------|-----|-----|-----|-----|-----|-----|-----|
|Program | 0 |File length|8000h/LINE |prog offset|
|Numeric array | 1 |File length| xxx |name | xxx | xxx |
|Character Array | 2 |File length| xxx |name | xxx | xxx |
|Code | 3 |File length| load addy | xxx | xxx |
|Snapshot | 4 |File length| xxx | xxx | xxx | xxx |
|Longfile | 5 | 32 bit file length | xxx | xxx |
|----------------|-----|-----------------|-----|-----|-----|
3, r_rdopen
Entry parameters: ix=ufia
Exit parameters: standard
Open a file on the MSDOS disc for reading. If the file has a standard +3 header, then this header is recognized, and the header block filled out accordingly. If no header is present and the file is <65536 bytes, then a header is faked such that it is a CODE file with load address 0.
4, r_rdbyte
Entry parameters: none
Exit parameters: a=byte
Read a byte from the currently open file.
5, r_rdblok
Entry parameters: de=address to load to
bc=number of bytes to read
h=page to load to
Exit parameters: none
Read a chunk of code from the currently open file to memory in the page given by h
6, r_wropen
Entry parameters: ix=ufia
Exit parameters: none
Open a file for reading, if the filetype in the ufia is specified as type 5, then no +3DOS style header will be created.
7, r_wrbyte
Entry parameters: a=byte to write
Exit parameters: none
Write the byte in a to the currently open file
8, r_wrblok
Entry parameters: de=address of block
bc=length of block
h=RAM page
Write a block of memory to disc
9, r_wrclos
Entry parameters: none
Exit parameters: none
Close the currently open file, write the directory entry and FAT.
10, r_erase
Entry parameters: ix=ufia
Exit parameters: none
Erase the files specified by the ufia - may be wild
11, r_snpload
Entry parameters: none
Exit parameters: none
Load the currently open reading file as a snapshot file, and execute accordingly.
12, r_mscat
Entry parameters: ix=ufia
Exit parameters: none
Catalogue a disc directory matching the specifications of the ufia.
13, r_mscatmem
Entry parameters: ix=ufia
de=address to place catalogue
Exit parameters: none
Catalogue the disc to an address in memory - make sure you have sufficient room for the catalogue!!! Initialise the memory with 0 before hand!!!
The format of the data supplied by the disc is unsorted and is as follows:
byte 0 - number of files in directory (0-255)
The filename information is as follows:
ds 11 - filename (without the ".")
ds 1 - directory flags
ds 2 - first cluster
ds 4 - file length (32 bit)
- As can be seen, each directory entry requires 18 bytes of space - this can amount to a lot - the routine does not respect RAM pages so if you're not careful you could overwrite the Slowdos code.
14, r_seldir
Entry parameters: de=path name
bc=length of path name
Exit parameters: none
Move to the directory described by that in de
Notes:
If successful all of the routines will return with carry set, if unsuccessful, carry will not be set, and a will hold the "rst 8" error code - apologies for this, but memory is very much at a premium!
The ufia (User File Information Area) is 20 bytes long and is ordered as follows:
+0 db drive (0,1) (irrelevant)
+1 db stream (for r_mscat)
+2 ds filename (12 characters including ".")
+14 db directory flags (irrelevant)
+15 db filetype }
+16 dw filelength } +3 header info
+18 dw start address/LINE/name }
+18 dw offset to BASIC }
Snapconv is small program for the +3 which decomposes snapshot files into smaller files that can be reconstructed to create a +3 BASIC loadable program.
To use it, simply copy a snapshot file from an MSDOS disc the default +3 drive, for practical purposes this must be A:.
If Snapconv is then loaded and the snapshot named entered, the snapshot will be decomposed into 4 separate files, with different extensions, but the same filename as the snapshot, these files are as follows:
Extension CODE parameters
.0 0,27 The registers detailed in Appendix I
.1 16384,6912 Screendump
.2 23296,1280 Printer buffer/BASIC area
.3 24576,40960 Main code
It is then up to you to use the parts as you desire!!