Header Reader - Alexander Livshits (Your Spectrum-Issue 4-Page ??)





Here's a routine that should prove useful to all Speccy users - for

the Basic programmer who's forgotten where a program is supposed

to start, the machine codist sizing up a certain piece of code

and, of course, the Microdriver attempting the tricky task of

converting software for operation on cartridge.

	When a program file is saved to tape it is stored in two blocks: the

first part, known as the file header, is always 17 bytes long and tells

the Speccy all it needs to know about the program block which

follows.

	This routine reads the header into high memory and decodes it

into a more meaningful form which is then displayed on-screen for

the user. The information provided is: the name of the program; the

type of program (Basic, code block, numerical or character array);

the destination address (if you are examining a code block) or the

program area (for Basic); the variables area; and the autostart line

number (if any).

	Should the program not find a file header, the message 'NOT A

HEADER' is dutifully printed on-screen.





Lines 60-80     The 'initial set-up' routine in which RAMTOP is lowered to

		27999. The two variables 's' and 'd' setup the machine code

		start address and the address to which the header is to be

		loaded, respectively. The function defined in line 70 performs

		a double byte PEEK (ie. this would be a DEEK on other

		computers).

Lines 90-95     Read in and POKE the machine code data to the address

		reserved for it.

Lines 100-150   The 'read header routine. This section of the program calls

		the machine code which reads the header into memory from

		location 'd' onwards. Line 150 sets the variable type to be

		equal to the first byte of the header.

Lines 159-200   Read in the header name from bytes 'd+1' to 'd+10' and

		print it.

Lines 210-230   Set up the following variables: 'len' - the file length; 'start'

		- the start address; 'pa' - the length of the variables area;

		and 'va' - the start of the variables area

Lines 239-280   Print details of the header for a Basic program file.

Lines 399-460   The part of the program which deals with the case of the

		header not being for a Basic program file. t$ is set to equal

		the file type. If it is a code file, line 440 prints the start

		address.

Lines 600-630   Lines 120 and 150 checked that the data read in was a

		header. And if it wasn't, then this routine prints the 'NOT A

		HEADER' message and the user is asked if another header is

		to be read in.



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TYPE: Utility 



COMMENT: 





This info file was typed by Jim Grimwood



Downloaded from:

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Maintained by:

Michael Bruhn -- frankie@image.dk