Microdrive Utilities

Microdrive Utilities





Jon Ellis with a Microdrive


toolkit for the Spectrum.





Although the Microdrive has been in widespread use with the


Spectrum for well over a year now, very little software


utilising the Microdrive has been published. The one kind


of routine which has received exposure is the extended Cat,


which gives information on the length and type of the files


on a cartridge. The programs in this article deal with the


Microdrive in a more sophisticated way.


The first two programs make up a secure saving system.


Files which are saved from the first program can only be


loaded using the second. Protected files cannot be seen on


a normal Cat, extended Cat programs reveal no valid


information, and the files cannot even be erased normally.


The third program is of more widespread application - it


eliminates the tortuous syntax of the normal Microdrive


commands, enabling you to load a file with an expression as


simple as


*LOAD "filename"


All of the new functions are implemented in the form of


new Basic commands so there are no Pokes required in ope-


ration. All of the commands are made up of a command word


preceded by a star, and followed by various parameters.


None of the new commands are keywords, and so they must be


typed out letter by letter.


Before you can enter a line containing one of the new


commands, you will have to make one USR call to insert the


new command interpreter. The address to call is different


for each program and is given in the paragraph describing


the program. This USR call will have to be placed at the


start of any program which uses the new Basic, and will


need to be re-executed after any NEW. All of the major


listings are given in the form of a hex-dump which is


designed for use with the hex loader given in listing 1.


[This program is on the .mdr which goes with this article,


under the obvious name of "hex loader".]


The task of programming was complicated by the fact that


there are at least two different shadow ROM programs in


existence. I have therefore given two listings for each of


the major programs. To find out which version of the shadow


ROM you have in your Interface 1, type in the bytes from


listing 2 using the hex loader. [This is on the .mdr as


"Version".] When you have finished, type


RANDOMIZE USR 40000


and the program will tell you which ROM you have. If you


have a version 1 ROM you should use listings 3a, 4a and 5a,


version 2 owners should use listings 3b, 4b and 5b. If you


have an unknown ROM then you will be unable to use the


programs.





The first program, given in listing 3, enables you to save


and erase files in the special protected format. The new


commands are *Dump to save a file, and *Wipe to erase one.


The USR call to invoke the two commands is


RANDOMIZE USR 64280


Before beginning to type in the bytes from listing 3a or 3b


you must


CLEAR 64279


to move Ramtop out of the way. This also applies when you


want to load the completed code for use in a program. When


you have finished entering the bytes, the code should be


saved:


SAVE *"m";1;"Safe=Save"CODE 64280,1080 <ENTER>


[Both a and b versions of this code are on the .mdr, as


"Safe=SaveA" and "Safe=SaveB". I've only been able to test


the b version, but the a code does at least checksum OK.]


The required syntax for the *Dump command is very similar


to that of the SAVE command referred to the tape system.


For example, the expression


*DUMP "file 1"


would save the current Basic program onto drive 1 in the


protected format. You may save to drives other than 1 by


the inclusion of a valid drive number and a semicolon


before the filename - the line


*DUMP 3;"file 1"


would have saved the program to drive 3. Note that all


filenames for use with the protected save system may be a


maximum of /nine/ characters in length.


The forms


*DUMP "filename" LINE,


*DUMP "filename"SCREEN$


and


*DUMP "filename"CODE


are supported, but *Dump "filename" DATA is not. When


saving code you can include an optional third parameter as


an autorun address for the code block - e.g.


*DUMP "game"CODE 30000,5000,31000


will save 5000 bytes of code starting at 30000. Immediately


on loading, the code will be executed from 31000. The other


command provided by this listing, *Wipe, required no para-


meters apart from the filename and an optional drive number


- the only allowed syntax forms being


*WIPE "filename


and


*WIPE 5;"filename"





Listings 4a and 4b contain the bytes for the other half


of this utility - the program which allows you to reload


protected files. Before beginning to type the bytes in you


must


CLEAR 64444


and likewise on any subsequent loading. When you have


finished, you should save the object code:


SAVE *"m";1;"Safe=Load"CODE 64445,920 <ENTER>


[On the .mdr as "Safe=LoadA" and "Safe=LoadB", and again


I've only been able to actually test the B version.]


This program provides only one new command, *Take, and


the required address that must be called to insert it is


64445. The only permissible syntax is


*TAKE "filename"


or


*TAKE 4;"filename"


If the Break key is pressed whilst the program is load-


ing a file then the machine will be reset.


I suggest that you experiment with the safe loading


system on a blank cartridge until you are sure that it is


working properly. Note that when a Basic program is *Taken


from cartridge, all its variables are loaded as well.





The final major program is the syntax simplifier. The bytes


are given in listing 5. Before typing in or loading the


object code you must


CLEAR 64879


When you have finished entering, the code should be saved:


SAVE *"Short Syn"CODE 64880,480 <ENTER>


[Same note as above: two versions, only b version tested.]


This program provides six new commands which are inserted


with the line


RANDOMIZE USR 64880


The six commands are *Save, *Load, *Verify, *Merge, *Erase


and *Format. These commands perform exactly the same func-


tions - with one exception - as their normal counterparts.


However, the clumsy "M";1; syntax has been abandoned. All


six commands have the drive number as an optional parameter


as in *Dump etc.


All the commands except *Save take exactly the same


syntax form as *Take and *Wipe. Note that, contrary to the


normal requirement, you do not need to state in a Load-type


command the kind of file you want to load - the program


automatically determines the nature of the incoming file,


and treats it accordingly. All the usual options for saving


screens, arrays and code are available with the *Save


command.


The *Erase command has an extra function - a wildcard


facility in the filename. As an example- if you had three


files on a cartridge called Block 1, Block 2 and Block 3,


you could erase all three in a single *Erase line:


*ERASE "Block ?"


The '?' character in the filename indicates that that par-


ticular character position need not be checked for a match


when searching the cartridge for records of the file to be


erased. Note that the line


*ERASE "??????????"


will erase all files on the cartridge.





Listing 6 is a sub-routine which enables you to have your


new commands give their own unique error messages. Each


error message should be added to the table with 80hex added


to the last character.


The messages are printed with a black square instead of


an error letter or number to indicate that they are non-


standard errors. The routine is activated from your program


by loading the location Error with the number of the


message in the table minus one, and then calling NewRR.


The new ROM /must/ be paged in when this routine is called,


otherwise a crash will occur - line 90.


Listing 7 is a command interpreter for building a library


of new Basic statements. It scans the table CMTAB for a


command, giving a syntax error if it is not found, and


jumping to the appropriate address if it is.


[Both these subroutines were given as assembler listings


only, not as pre-assembled machine code. They also provide


sample data only, and as such are not usefully assemblable


in the state they are in - they're useful only as a start


for your own programs. Therefore, I'm giving them here in


their assembly format, and they are not on the .mdr.]


___________________________________________________________


Listing 6.


00010 ;***********************


00020 ;** NEW ERROR SYSTEM **


00030 ;** by Jon Ellis 1985 **


00040 ;***********************


00050 ORG address


00060 NEWRR LD SP,(23613)


00070 LD HL,HANDL


00080 EX (SP),HL


00090 RST 0


00100 HANDL LD HL,(23755)


00110 LD (23645),HL


00120 RES 5,(IY+1)


00130 LD HL,0


00140 LD (IY+55),H


00150 LD (23563),HL


00160 INC HL


00170 LD (23574),HL


00180 CALL 5805


00190 CALL 3438


00200 SET 5,(IY+2)


00210 LD A,143


00220 RST 16


00230 LD A,32


00240 RST 16


00250 LD A,(ERROR)


00260 LD DE,ERTAB


00270 JP 4934


00280 ;________________________


00290 ;************************


00300 ;** ERROR MESSAGES **


00310 ;************************


00320 ERROR DEFB 0


00330 ERTAB DEFB 128


00340 DEFM /Example /


00350 DEFM /messag/


00360 DEFB "e+128


P0


___________________________________________________________


Listing 7.


00010 ;***********************


00020 ;** COMMAND SEARCHER **


00030 ;** by Jon Ellis 1985 **


00040 ;***********************


00050 ORG address


00060 VECTR RST 8


00070 DEFB 49


00080 LD HL,NWCOM


00090 LD (23735),HL


00100 RET


00110 NWCOM RST 16


00120 DEFW 24


00130 CP "*


00140 JR NZ,NFIND


00150 LOOK LD B,number


00160 LD HL,CHTAB


00170 LOOP1 PUSH BC


00180 LD DE,(23645)


00190 NXLET PUSH HL


00200 RST 16


00210 DEFW 32


00220 POP HL


00230 XOR (HL)


00240 JR Z,LETOK


00250 XOR 32


00260 JR NZ,WRONG


00270 LETOK INC HL


00280 LD A,(HL)


00290 CP "=


00300 JR NZ,NXLET


00310 INC HL


00320 LD E,(HL)


00330 INC HL


00340 LD D,(HL)


00350 RST 16


00360 DEFW 32


00370 EX DE,HL


00380 POP BC


00390 JP (HL)


00400 WRONG LD (23645),DE


00410 LD B,255


00420 LD A,"^"


00430 CPIR


00440 POP BC


00450 DJNZ LOOP1


00460 NFIND JP 496


00470 ;_____________________


00480 ;*********************


00490 ;** COMMAND TABLE **


00500 ;*********************


00510 CMTAB DEFM /EXAMPLE=/


00520 DEFW EGRUN


00530 DEFB "^"


P0